Abstracts in the Bethia King Lab
King, BH. 2018. Benefit of polyandry in a monandrous species when females mate with already mated males. Behavioral Ecology and Sociobiology.
Female mating frequency varies among animal taxa. A benefit to females of remating has usually been found, but almost all tests have been with polyandrous species. A species being monandrous does not guarantee that mating only once benefits the female, instead the monandry may result from sexual conflict, where her failure to remate benefits her mate, but not her. The parasitoid wasp Spalangia endius (Hymenoptera: Pteromalidae) is highly monandrous. Females do not benefit from either immediate or delayed remating when their first mate is virgin. However, some females are likely to mate with already mated males because sex ratios are female-biased. Here the effect of experimentally-induced polyandry on female fitness was examined for females whose first mate had already mated four times, i.e., for fifth females. Fifth female S. endius produce significantly fewer daughters than first females. Production of daughters, but not sons, requires sperm in hymenopterans. Fifth females were experimentally induced to mate with a second male, by preventing such females’ first mate from providing postcopulatory courtship. The proportion of female offspring produced by these polyandrous fifth females was greater than by monandrous fifth females and not significantly different than by monandrous first females. Total number of offspring did not differ among the three treatments. These results show that there are conditions under which females benefit from polyandry in this highly monandrous species and that the benefit is through effects on offspring sex ratio, not fecundity.
King BH, Miller KA. 2018. Mating status effects on sexual response of males and females in the parasitoid wasp Urolepis rufipes. Journal of Insect Behavior doi:10.1007/s10905-018-9667-z
Although mate preferences are most commonly examined in females, they are often found in both sexes. In the parasitoid wasp Urolepis rufipes, both female and male mating status affected certain aspects of sexual interactions. Female mating status mattered only in the later stages of mating. Males did not discriminate between virgin and mated females in terms of which they contacted or mounted first. However, once mounted, most virgin females were receptive to copulation, whereas very few mated females were. Whether a male’s mating status affected his own sexual response depended on the female’s ability to respond and the stage of mating. Examining male behavior toward dead females allowed elimination of the role of female behavior in how males responded. Virgin and mated males are both attracted to dead females as evidenced by their fanning their wings at such females. However, mated males were quicker than virgin males to contact and to mount in an experiment with dead females, whereas there was no such differential response in an experiment with live females. This difference is consistent with greater female sexual responsiveness to virgin males. Male mating status also affected female receptivity to copulate. Once mounted, live virgin females were less likely to become receptive to copulation by mated males than to virgin males, but only in a choice experiment, not in a no-choice experiment.
Burgess ER, King BH. 2017. Insecticidal potential of two sugar alcohols to Musca domestica (Diptera: Muscidae). J Econ Entomol 110:2252–2258
Pest management plans for house flies, Musca domestica L. (Diptera: Muscidae), often include insecticides. Because of resistance and environmental concerns with traditional insecticides, safe new pesticides and pesticide formulations are needed. The insecticidal potential of two sugar alcohols, xylitol and erythritol, against adult house flies was assessed. Flies consumed both xylitol and erythritol. The proportion of flies that exhibited the proboscis extension reflex, which is associated with feeding, did not differ significantly between the sugar alcohols and sucrose in an experiment with 20% solutions and older flies, but was less for the sugar alcohols in an experiment with 2M solutions and younger flies. When presented alone or mixed with sucrose, both sugar alcohols significantly decreased fly survival relative to just sucrose. There was a strong negative relationship with concentration and mean days survived for xylitol, but no significant relationship for erythritol or sucrose. Relative to sucrose alone, a temporary exposure to xylitol, but not to erythritol, decreased survival when sucrose was subsequently available. Although xylitol and erythritol can both decrease survival of house flies and would meet the criteria for organic farming, deaths were often not very immediate. However, continued investigation of a variety of sweeteners as feeding-stimulant alternatives to sucrose is still useful, to minimize the risk of house flies evolving resistance to the sugar in baits. Our analysis of already published data on house flies that had been repeatedly exposed to a sucrose-based bait is consistent with the evolution of sucrose-feeding avoidance.
Burgess IV E, Kremer A, Elsawa SF, King BH. 2016. Sublethal effects of imidacloprid exposure on Spalangia endius, a pupal parasitoid of filth flies. BioControl. doi: 10.1007/s10526-016-9776-6
Parasitoids and neonicotinoids can both suppress economically harmful filth fly populations. However, sublethal effects of neonicotinoids have not previously been studied for commonly used species of filth fly parasitoids. Exposure to an LC50 of imidacloprid decreased the ability of surviving individuals of the parasitoid wasp Spalangia endius Walker (Hymenoptera: Pteromalidae) to kill house fly pupae under some conditions. In an unburied-hosts experiment, significantly more flies and fewer parasitoids emerged in the LC50 imidacloprid treatment versus the LC10 or controls; parasitoid sex ratio and longevity were not affected. However, in a buried-hosts experiment, parasitoid and fly emergence were independent of treatment. ELISA (enzyme-linked immunosorbent assay) showed lower imidacloprid residues in or on parasitoids exposed to the media in which hosts were buried. Our findings suggest that substrate may reduce pesticides on biological control agents that burrow, making them more effective.
Broski S and King BH. 2016. Effects of size and age of the host Musca domestica (Diptera: Muscidae) on production of the parasitoid wasp Spalangia endius (Hymenoptera: Pteromalidae). Journal of Economic Entomology, doi.org/10.1093/jee/tow246 http://jee.oxfordjournals.org/content/by/year
One method of control of house flies, Musca domestica L. (Diptera: Muscidae), and other filth flies is by repeated release of large numbers of pupal parasitoids such as Spalangia endius Walker. Rearing these parasitoids may be facilitated by understanding how host factors affect their production. Previous studies have examined the effects of host size and host age on parasitoid production, but have not examined the interaction between host size and host age or the effects with older females, which may be less capable of drilling tough hosts. Females were given hosts of a single size-age category (small young, small old, large young, or large old) for two weeks. The effect of host size and of host age on parasitoid production depended on female age. On their first day of oviposition, females produced more offspring from large than from small hosts, but host age had no significant effect. The cumulative number of parasitoids produced in the first week was not significantly affected by host size or host age. However, the cumulative number of parasitoids produced over two weeks was affected by both host size and host age, with the greatest number of parasitoids produced from small young hosts. Thus not only are smaller hosts cheaper to produce, but these results suggest that their use may have no effect or a positive effect on the number of parasitoids that can be produced when females are ovipositing for a week or two.
Wittman TN, Miller KAK, King BH. 2016. Finding prospective mates by the parasitoid wasp Urolepis rufipes (Hymenoptera: Pteromalidae). Environmental Entomology. DOI: 10.1093/ee/nvw136
Cues from emergence sites may be predictive of mating opportunities if potential mates are slow to disperse after emergence, and particularly if emergence sites are clumped, as in the solitary parasitoid wasp Urolepis rufipes Ashmead. Males emerge before females, and the present study suggests that males may use emergence sites of conspecific males to locate mates. In choice experiments, virgin males spent more time on a male-emerged host (a host from which a male had recently emerged) than on a female-emerged host. Relative to when no host was present, virgin males also marked more in the presence of a male-emerged host, but did not mark more in the presence of a female-emerged host. Females, but not other males, are known to be attracted to male marks. Unlike for males, there was no evidence that females distinguished between male-emerged and female-emerged hosts. Virgin females preferred areas where multiple males had marked over areas where a single male had marked. Such areas had more total marks, yet marks per male did not differ between aggregated and solitary males. Thus, through his own attraction to male-emerged hosts and by marking near other males a male may find and attract females, and with no apparent increase in the cost of attraction.
Burgess IV E, King BH. 2016. Behavior and survival of the filth fly parasitoids Spalangia endius and Urolepis rufipes (Hymenoptera: Pteromalidae) to three granular house fly baits and components. Environmental Entomology.
Behaviors and mortality of two filth fly parasitoid wasps, Spalangia endius Walker and Urolepis rufipes Ashmead, were tested in response to granular fly baits containing one of three active ingredients (AI): Golden Malrin (methomyl), QuickBayt (imidacloprid), or Quikstrike (dinotefuran). Behavioral responses to each of two components of the baits, the AIs and the fly attractant pheromone (Z)-9-tricosene, were also examined independently. S. endius avoided contact with bait granules, regardless of bait type. However, when S. endius contacted bait residue, the imidacloprid bait appeared to be the least harmful of the baits for S. endius, at least in the short term. S. endius was attracted to imidacloprid by itself. However, S. endius avoided (z)-9-tricosene. In contrast to S. endius’ attraction to imidacloprid, S. endius neither avoided nor was attracted to methomyl or dinotefuran. For U. rufipes, the methomyl bait appeared to be especially harmful. U. rufipes avoided bait granules with imidacloprid or dinotefuran but not with methomyl, died quickly in the presence of methomyl bait residue, and had a methomyl LC50 that was lower than that for S. endius. The avoidance by U. rufipes of granules with imidacloprid or dinotefuran appears to be related to components other than the AIs or the (Z)-9-tricosene because U. rufipes did not avoid either individually. The behavioral avoidance of the parasitoids in the present study occurred despite no exposure recently, if ever, to these pesticides.
Burgess IV, ER; King BH. 2015. Compatibility of the parasitoid Spalangia endius (Hymenoptera: Pteromalidae) and insecticides against Musca domestica (Diptera: Muscidae) as evaluated by a new index. Journal of Economic Entomology, DOI: http://dx.doi.org/10.1093/jee/tov104
Various insecticides for the control of the house fly Musca domestica L. were tested for compatibility with a biological control agent, the pupal parasitoid Spalangia endius Walker. Bioassays used the mode in which each organism was expected to be harmed by the insecticides, a surface contact bioassay for S. endius and a feeding bioassay for M. domestica. A Pesticide Compatibility Index (PCI) was created that allows comparison of LC50 values when the mode of exposure to a pesticide differs. First LC50 values were converted into units of prescribed dosages (LPR=LC50-to-prescribed dosage ratio). This study used dosages from labels of granular baits. PCI is the ratio of LPRbiological control agent to LPRpest. For these PCI values, order of compatibility with S. endius was spinosad>thiamethoxam>dinotefuran>methomyl>imidacloprid. That spinosad was better than imidacloprid or methomyl, both for parasitoid survival and for killing flies, is consistent with conclusions from the LC50 values. Permethrin and nitenpyram were also tested, but their PCIs were not calculated. Permethrin is prescribed as a contact insecticide against flies rather than being consumed as a bait, and nitenpyram has not been formulated as a fly insecticide. Compared with the other insecticides in terms of LC50 values, permethrin was moderately toxic to S. endius but one of the most toxic for M. domestica, whereas nitenpyram was least toxic for both S. endius and the flies.
Broski S, King BH. 2015. Drilling-in and chewing-out of hosts by the parasitoid wasp Spalangia endius (Hymenoptera: Pteromalidae) when parasitizing Musca domestica (Diptera: Muscidae). Environmental Entomology 1–9 (2015); DOI: 10.1093/ee/nvv069
Many organisms are protected from natural enemies by a tough exterior. Such protection is particularly important for immobile stages, such as pupae. The pupa of some insects is protected by a puparium, which is a shell formed from the exoskeleton of the last larval instar. However, the puparium of certain fly species is drilled through by adult females of the wasp Spalangia endius Walker. The female wasp then deposits an egg on the fly pupa within the puparium. After the wasp offspring finishes feeding on the fly pupa, it chews through the puparium to complete emergence. Despite the apparent toughness of the puparium, there was no detectable wear on the ovipositor of S. endius females even when females had been encountering fly pupae (Musca domestica L.) for weeks, and regardless of whether the pupae were large or old or both. Energy dispersive spectroscopy did not reveal any metal ions in the ovipositor’s cuticle to account for this resistance against wear. Offspring of S. endius that chewed their way out of pupae also showed no detectable wear on their mandibles. Tests with a penetrometer showed that the force required to penetrate the center of a puparium was greater for larger and for older pupae; and an index of overall thickness was greater for large old pupae than for small old pupae. The lack of an effect of pupal size or age on wear may result from wasps choosing locations on the puparium that are easier to get through.
Cooper J, King BH. 2015. Substrate-borne marking in the parasitoid wasp Urolepis rufipes (Hymenoptera: Pteromalidae). Environmental Entomology 1–9 (2015); DOI: 10.1093/ee/nvv017
Many animals use pheromone marking as a way to identify their territory or other resources. Among insects, substrate-borne marking is frequently reported for females, which in many species make marks containing oviposition deterring pheromone, which other females avoid. However, there are fewer reports of substrate-borne marking for males. Here marking in males of the parasitoid wasp Urolepis rufipes (Ashmead) is described. The conditions under which males mark and whether males and females respond to the males’ marks were examined using behavioral observations. Males marked by dragging the tips of their abdomens across a substrate. They marked much more after mating and after consuming honey. They also marked more when with a female irrespective of copulation, although not when with a male. Females spent more time on or near marked substrates, and males also responded to their own marks. Although males aggressively and successfully defended areas that they had marked against other males, males did not respond to another male’s marks in the conspecific’s absence. In contrast to males, females did not mark, either on the surface of hosts or on other surfaces; and males showed no detectable response to surfaces which females had recently occupied.
King, B. H., Kolyott, K. L., Chesney, A. R. 2014. Livestock bedding effects on two species of parasitoids (Hymenoptera : Pteromalidae) of filth flies. Journal of Insect Science Abstract. Choice of livestock bedding has been shown to affect density of filth fly maggots. Here laboratory experiments indicate that bedding type can also affect natural enemies of the flies, specifically the parasitoid wasps Spalangia endius Walker and Urolepis rufipes (Ashmead) (Hymenoptera: Pteromalidae) parasitizing a natural host, the house fly Musca domestica L (Diptera: Muscidae). For both parasitoid species, when females parasitized hosts under bedding, cedar shavings resulted in more flies and fewer parasitoids compared to pine shavings, but pine shavings did not differ from wood pellets and corn cob pellets. In the absence of exposure to hosts, longevity of adult females was reduced in cedar shavings compared to pine shavings and pellets. In contrast to the effects on parasitization and on adult survival, shavings treatment had no significant effect on the number of parasitoids or flies that emerged when hosts were not exposed to shavings until after parasitization.
Moran RL, vonEnde CN, King BH. 2014. Seasonal colour and anti-predator behaviour (Percidae: Etheostoma). Journal of Fish Biology 84:1188–1194. doi:10.1111/jfb.12327
This study examined how colour varies across season and sex in the fantail darter Etheostoma flabellare and the banded darter Etheostoma zonale. Etheostoma flabellare has male-only parental care and exhibited slight sexual dimorphism in overall colour, with no discernible effect of season on colour; whereas E. zonale does not have parental care and exhibited substantial sexual dimorphism in colour, but only in the breeding season. Additionally, antipredator behaviour of E. zonale was compared between males that were fully coloured during the breeding season and males that were partially coloured at that time, but the effects of colour and season were not consistent across males.
Mowles SL, King BH, Linforth RST, Hardy ICW, 2013. A female-emitted pheromone component is associated with reduced male courtship in the parasitoid wasp Spalangia endius. PLoS ONE 8 e82010. doi:82010.81371/journal.pone.0082010.
During courtship interactions, the courted individual may not always be prepared to mate. For example, mating or courtship may be detrimental to its fitness and resistance is expected under these circumstances. As such, various resistance strategies have evolved, from physically fending off courting individuals to producing behavioural signals of unreceptivity. In the parasitoid wasp Spalangia endius, females rarely re-mate and mated females are avoided by males in favour of virgin females. Further, mated females appear to advertise their mating status by the release of a pheromone component (methyl 6-methylsalicylate), but direct evidence of the nature of this release is lacking. Here we used real-time chemical analysis to track the emission of the pheromone component during courtship interactions between virgin males and either virgin or mated females. We found that females actively release methyl 6-methylsalicylate when courted and that significantly greater concentrations are released by previously mated females. Further, high concentrations of this component are associated with both the prevention and termination of courtship.
Moran RL, vonEnde CN, King BH. 2013. Mate choice copying in two species of darters (Percidae: Etheostoma). Behaviour. DOI
Abstract. Mate choice copying is a form of social learning that is defined as the increased likelihood of an individual choosing a particular mate after observing another individual choosing that mate. Mate choice copying has been demonstrated in a range of taxonomic groups, but not usually for both sexes. Mate choice copying experiments were performed here using two congeneric sympatric darters, Etheostoma flabellare and E. zonale. In E. flabellare, males guard a nest site under a rock and care for developing eggs. In E. zonale, eggs are attached to filamentous green algae and neither sex provides parental care. Our results provide the first evidence that mate choice copying occurs in darters. Previously it was hypothesised that copying might be more common in species and sexes that provide parental care, the reasoning being that the costs of choosing poorly may be higher. However, mate choice copying was found in both sexes of E. zonale (no parental care) and in male but not female E. flabellare (male only parental care). Thus, the only group that did not mate choice copy was the one whose mate would be providing care, and even E. flabellare females copy the mate choice of other females by some definitions. The relationship, if any, between which sex provides parental care and whether copying occurs remains unclear, and the number of species for which such data are available is limited.
Cooper, J. Burgess IV, E. R. and King, B. H. 2013. Courtship behavior and detection of female receptivity in the parasitoid wasp Urolepis rufipes. Journal of Insect Behavior. DOI 10.1007/s10905-013-9390-8 Once a Urolepis rufipes male mounted, the female beat her antennae against his mouth and clypeus. Immediately after he swept his antennae rapidly downward and extruded his mouthparts, her abdomen rose as she opened her genital orifice. Almost simultaneously he backed up for copulation and she folded her antennae against her head. Neither her abdomen rising nor her antennal folding were essential to his backing up as determined from their timing and from experiments in which her abdomen was sealed or her antennae were removed. Females did not open their genital orifice if with a sealed-mouth male; and antennae-removed females did not open even in the few cases where untreated males extruded their mouthparts. Unlike a closely related species, females mounted by sealed-mouth males did not open in response to air from containers of mating pairs.
King, B. H. and Kuban, K. E. 2012. Should he stay or should he go: male influence on offspring sex ratio via postcopulatory attendance. Behavioural Ecology and Sociobiology 66: 1165–1173. DOI:10.1007/s00265-012-1369-5 In species without nuptial gifts or parental care, postcopulatory attendance of females by males has generally been interpreted as males guarding against sperm competition. Guarding benefits may be concurrent with attendance (the guarding now hypothesis) or male behavior during attendance may make the female unreceptive (the guarding in absentia hypothesis). However, in addition to guarding functions, attendance may provide the male with an opportunity to influence the female's use of sperm. In haplodiploids such as hymenopterans, doing so may be beneficial because only daughters and not sons are produced sexually and so influence male reproductive success (the sex ratio hypothesis). In the parasitoid wasp Urolepis rufipes, postcopulatory attendance involved the male remaining mounted after copulation and resuming courtship. Support for the guarding now hypothesis was limited. A male's presence on a female did not reduce the probability, or quickness, of another male mounting, and second-mounted males frequently copulated. The guarding in absentia hypothesis was not supported. Females became unreceptive soon after mating even when copulation and postcopulatory attendance were experimentally prevented. The sex ratio hypothesis was supported. Postcopulatory attendance caused females to produce more daughters. They also produced more total offspring. Thus, a male should stay and should not go even in the absence of other males, at least when opportunities for other matings are absent as in the present study. Although most studies of offspring sex ratios have focused on maternal control, this study provides an example of apparently adaptive male influence on sex ratio.
Fischer CR and King BH. 2012. Inhibition of male sexual behavior after interacting with a mated female. Behaviour 149:153-169
Abstract. A male's reproductive success is generally highly dependent on his mating success. Nevertheless, there may be times during a male's life when his sexual responsiveness ebbs. In the parasitic wasp Spalangia endius, after a male mates, he shows a temporary decrease in his sexual responsiveness to even virgin females. We examined behavioral mechanisms for the decrease. 1) Decreased sexual responsiveness is not simply a result of habituation to attractive features of females during mating. If it was, males that had courted dead virgin females for substantially longer than during a normal mating should have been detectably less sexually responsiveness than males that had not courted, but they were not. 2) Decreased sexual responsiveness also is not a learned aversion to females that results from female brush-off, in which females use their hind legs to dislodge mounted males after copulation. Sexual responsiveness was reduced by mating regardless of brush-off. 3) Male S. endius are known to avoid mounting mated females, and surprisingly, the responsiveness of a virgin male decreased even when he had briefly approached and then retreated from an already mated female, i.e., even in the absence of mounting or copulation. This suggests that the aversive stimulus that causes males to retreat from mated females is also involved in the male's subsequent sexual inhibition.
King, B. H. and M. A. Owen. 2012. Post-mating changes in restlessness, speed and route directness in males of the parasitoid wasp Spalangia endius (Hymenoptera: Pteromalidae). Journal of Insect Behavior 25:309-319. Abstract. Changes in movement patterns can affect the probability of encountering resources, including mates. This study examined movement in males of the parasitoid wasp Spalangia endius, specifically changes in locomotion after mating that could be responsible for males' post-mating sexual inhibition to approach a female. In the presence of a female, mated males were faster moving than virgin males, which by itself would make them quicker, not slower, to reach her. However, mated males also tended to be less restless (i.e., spent less of their time locomoting) and their paths were less direct, both of which would make them slower to reach her. In contrast, in the absence of a female, having recently mated had no significant effect on restlessness, speed or path-directness. Thus the post-mating locomotor changes in males appeared not to be intrinsic changes but rather changes in how they responded to females. Video recordings were corrected for aspect ratio prior to analyses.
Nichols WJ Jr, Bartelt RJ, Cossé AA, King BH. 2010. Methyl6-methylsalicylate: a female-produced pheromone component of the parasitoid wasp Spalangia endius. Journal of Chemical Ecology 36:1140-1147.
Abstract. Sex-pheromone-related behavior and chemistry were studied in the wasp Spalangia endius Walker (Hymenoptera:Pteromalidae), a pupal parasitoid of the house fly, Musca domestica L. (Diptera: Muscidae). Males responded behaviorally to female extracts by arrestment, whereas females did not arrest to male extracts. In acomparison of male and female extracts by gas chromatography-mass spectrometry (GC-MS), two female-specific compounds were found. One was identified as methyl 6-methylsalicylate (gas chromatographic retention time and mass spectrum versus an authentic standard), but the chemical structure of the second compound is still unknown. Male antennae were sensitive to both compounds in electrophysiological tests (GC-EAD). Males responded behaviorally to methyl 6-methylsalicylate by arrestment, but they did not arrest to the second compound. Methyl 6-methylsalicylate has been reported previously from some ant and beetle species, but never from the Pteromalidae. Chemical analysis of the extracts and the male behavioral results are consistent with the hypothesis that methyl 6-methylsalicylate functions as a female-emitted pheromone component at short range, but the exact role of both compounds in intersexual interactions in S. endius remains to be determined.
King BH. 2010. Which sex controls the duration of postcopulatory courtship and to what effect in the parasitoid wasp Spalangia endius. Behaviour 147:993-1007. Summary. Resistance by females during a reproductive interaction is thought to reflect conflict between the sexes over the optimal outcome. In the parasitoid wasp Spalangia endius, the female attempts to brush the male off her back with her hind legs after a few seconds of postcopulatory courtship. Although males do not dismount immediately, this signal is effective. Removal of female hind legs resulted in postcopulatory courtship that was longer, although a normal duration was sufficient to turn off a female's receptivity permanently. Responding immediately to the signal was not advantageous to males. When postcopulatory courtship was experimentally terminated as soon as females began signalling, they sometimes remained attractive and receptive to subsequent males. However, earlier studies suggest that for most if not all females, mating a second time would not increase the production of daughters or of total offspring, and being mounted interferes with oviposition. Thus the normal duration of postcopulatory courtship is determined by the behaviour of both the male and the female, and currently this may usually be better for both partners than a duration determined by just one partner. Coevolution between the sexes may have mitigated previous conflict, and remaining resistance may reflect the ghost of conflict past.
King.B. H. and Bressac, C. 2010. No fitness consequence of experimentally induced polyandry in a monandrous wasp. Behaviour 147:85-10.
Abstract. Tests of the effects of multiple mating by females on female fitness have been primarily with polyandrous species, where a benefit to multiple mating has usually been found. In contrast, no such benefit was found here for the parasitic wasp Spalangia endius, a highly monandrous species. Females that mated only once prior to oviposition exhibited a rapid decline in daughter production long before they died. The production of daughters, but not sons, is sexual in this species, i.e., requires sperm. Nevertheless, females with greatly decreased daughter production did not then remate. When such females were experimentally manipulated into copulating with a second male, additional sperm were stored in the femalesï¿½ sperm storage organs. However, this sperm increase had no significant effect on daughter production, total offspring production or longevity. There was no evidence that either immediate or delayed polyandry currently benefits females. The lack of benefit may be a general feature of highly monandrous species or a common feature of parasitic hymenopterans regardless of mating system.
King, B. H. and Fischer, C. R. 2010. Male mating history: effects on female sexual responsiveness and reproductive success in the parasitoid wasp Spalangia endius. BehaviouralEcology and Sociobiology.
Abstract. Males frequently mate multiply, but are there negative fitness consequences for their later mates? Potential costs include less sperm and less nutrition. In most hymenopterans, daughters, but not sons, are produced sexually. This mean that effects of being a later mate on sperm received versus on nutrients received should be distinguishable. If later mates receive less sperm, it should manifest as a reduction in daughter production, whereas a reduction in nutrients should affect production of both sexes. Any cost to being a later mate may in turn select for polyandry or for female choice of virgin males. Males of the parasitoid wasp Spalangia endius were presented with up to five females in succession. Offspring production was compared among first, third and fifth females; and it did not differ. However, about half of fifth femaleshad begun producing only sons by their tenth day, whereasfirst and third females rarely had. Despite the reduction in daughter production, even fifth females rarely remated. However, females tended to mate with virgin males rather than mated males when given a choice. This tendency was dependent on male, not female, behavior, but should benefit the female nevertheless. Sex ratios in this species are one male for every one and a half to three females. Thus the number of times that males could mate before daughter production was reduced coincided roughly with the mean number of times that males likely mate in this species. Nevertheless, some females are likely to experience the cost of being a fifth female because of skewed mating success among males.
King.B. H. 2008. Effects of sex and mating status on who initiates contact in the parasitoid wasp Spalangia endius (Hymenoptera: Pteromalidae). Journal of Insect Behavior 21:387-393
Abstract. In species without obvious aggression, individuals may still vary in how likely they are to initiate contact with a conspecific. In the parasitoid wasp Spalangia endius, who was more likely to initiate contact during pair wise interactions depended on sex and mating status. Specifically, more contacts between the sexes were initiated by the male than by the female both when the female was still virgin and when the female had already mated with a different male. After a male mated with a given female, he still sometimes initiated contacts with her, but no longer more often than she did. A male was more likely to initiate contact when he was with a female than when he was with another male, and he was more likely to retreat from a mated female than from a male.
King, B. H. and Dickenson, R. M. 2008. Functional and nonfunctional female receptivity signals in the parasitoid wasp Spalangia endius. Environmental Entomology. 37:782-786.
In many taxa, females signal during courtship when they are receptive. However, just because a female signals does not mean that the male responds to the signal. This study examines female signaling of receptivity (readiness to copulate) and male response in the parasitoid wasp Spalangia endius Walker. Females folded their antennae against their heads when they were receptive, and antennal folding has been shown to be effective in eliciting male copulation attempts in aconfamilial. However, male S. endius did not respond to antennal folding: males did not contact the femaleï¿½s antennae during courtship, and how quickly a male attempted copulation was independent of whether or not the female had antennae. Males courted from on top of the femaleï¿½s abdomen and appeared to detect receptivity directly from the femaleï¿½s abdomen rising as her genital orifice opened. On females whose abdomens did not rise, initiation of male copulation attempts were delayed, although not eliminated. Based on its current lack of function as a receptivity signal and on comparisons to published reports of mating behavior in confamilials, we hypothesize that female antennal folding at receptivity is a vestigial trait in S. endius.
King, B. H. and Dickenson, R. M. 2008. A behavioral study of the proximal mechanisms of male recognition of female mating status in the parasitoid wasp Spalangia endius (Hymenoptera: Pteromalidae). Annals of the Entomological Society of America
Mating preferences, including the proximate mechanisms of preferences, have not been well-studied among parasitoid wasps. In the parasitoid wasp Spalangia endius Walker, males chase after both mated females and virgin females equally. Not until contact or near contact are males more likely to retreat from mated females and hence less likely to mount themtest several hypotheses about the proximal cause of such retreats. Retreats do not appear to be a response to aggressive physical behavior by mated females. Male retreats also were not just a response to female motion; females were not consistently moving or consistently still prior to male retreats. Retreats were not simply a response to antiaphrodisiac pheromone on the surface of mated females; males did not avoid mounting dead females. If a pheromone is involved, females appear to be actively releasing it, in contrast to the antiaphrodisiac surface pheromones known in other hymenopterans. The mated female's head and thorax, but not her abdomen, were essential to unattractiveness at the mounting stage of mating.
Fischer, C. R. and King, B. H. 2008.Sexual inhibition in Spalangia endius males after mating and time for ejaculate replenishment. Journal of Insect Behavior 21:1-8.
Although males are often stereotyped as always sexually responsive, a previous study with the parasitoid wasp Spalangia endius showed that males exhibit a post-mating decrease in sexual responsiveness. The present study examined the duration of the decrease and whether waiting to remate increased the amount of ejaculate that a male provided to his second mate. Mated males were back to being as sexually responsive as virgin males by about 5 min after mating. The amount of ejaculate that females received from already mated males was not significantly related to the duration between the male's first and second mating. The short-term decrease in sexual responsiveness of a mated male may prevent him from immediately trying to remate with the same female because it gives her time to get away.
King B. H. 2007. The effect of exposure to conspecifics on restlessness in the parasitoid wasp Nasonia vitripennis (Hymenoptera: Pteromalidae). Canadian Entomologist 139:678-684.ï¿½
When habitat quality is variable, there should be strong selection for the ability to detect and respond to the variation. Adult females of the parasitoid wasp Nasonia vitripennis (Walker) (Hymenoptera: Pteromalidae) are known to increase their restlessness (the proportion of time in locomotion) both during and after exposure to a poor quality host. Doing so provides a mechanism for leaving a poor host and potentially finding a better host. This study examined whether restlessness also changes in response to competition as indicated by the presence of adult conspecifics. Both restlessness and the probability of dispersing across an inhospitable environment were greater when a female was with another female than when she was alone. However, restlessness did not remain elevated after the other female was removed. In contrast to females, restlessness of males did not increase either during or after exposure to other males, and the probability of dispersing across an inhospitable environment was unaffected by another male's presence. The difference between females and males may be related to differences in dispersal ability and in the abundance and distribution of hosts versus mates.
King.B. H. and M. E. Napoleon. 2006. Using effects of parasitoid size on fitness to test a host quality model assumption with the parasitoid wasp Spalangia endius.ï¿½ Canadian Journal of Zoology 84:1-5.
How body size affects fitness of males relative to females is relevant to understanding the evolution of sexual size dimorphism and maternal sex ratio manipulation. In most parasitoid wasps, mothers oviposit a greater proportion of daughters in larger hosts. The host quality model describes how this may be adaptive. A major assumption of the model is that host size has a greater effect on the fitness of daughters than sons. The assumption has often been tested indirectly by examining effects of parasitoid size on fitness because a parasitoid's size generally increases with the size of the host on which it develops. The validity of this indirect method is examined here for the parasitoid wasp Spalangia endius Walker, 1839 parasitizing Musca domestica. If the method is valid, effects of parasitoid size on fitness should match the effects of host size on fitness that were found in a previous study. The effects matched in that both parasitoid size and host size affected the fitness of females but not males. However, the aspects of female fitness that were affected differed. That female size but not male size affected fitness was consistent with the female-biased sexual size dimorphism of S. endius.
King. B. H. 2006. Mate location and the onset of sexual responsiveness in the parasitoid wasp Spalangia endius (Hymenoptera: Pteromalidae). Environmental Entomology 35:1390-1395.
In some animals, transformation to the adult stage occurs in a hidden location, such as a burrow or a host. Males that can locate hidden females sooner, e.g., before they emerge, may have a mating advantage, particularly if the females are ready to mate. Whether males locate pre-emergent females and whether pre-emergent females will mate was examined in the parasitoid wasp Spalangia endius Walker. S. endius parasitize fly pupae. A single wasp offspring feeds, pupates and transforms into an adult within the fly puparium (an outer shell around the fly pupa), and males emerge a day or more before females. Whether pre-emergent wasps are ready to mate was examined by dissecting them out of their hosts and then presenting them with naturally emerged adults of the opposite sex. Many of the pre-emergent wasps were ready to mate. Nevertheless, males did not distinguish between hosts containing a pre-emergent female versus a pre-emergent male, or even between parasitized and unparasitized hosts. In contrast, males were able to differentiate between hosts from which a female versus a male had recently emerged. Although females are ready to mate before emergence, there may be little advantage to recognizing and staying with a host that contains a pre-emergent female because emergence takes so long, which raises the cost of missed mating opportunities elsewhere.
King, B. H. and H. Leaich. 2006. Variation in propensity to exhibit thanatosis in Nasonia vitripennis. Journal of Insect Behavior 19(2):241-249.
Thanatosis (death-feigning) has rarely been documented for Hymenoptera but occurs in the parasitoid wasp Nasonia vitripennis. The propensity to exhibit thanatosis did not differ with age, sex, or food deprivation. Squeezing a female's abdomen and contacting her antennae were equally likely to trigger thanatosis. Dropping an object next to a female in order to cause substrate vibrations never triggered thanatosis, and dropping a female from a test tube rarely triggered thanatosis. Thanatosis was not seen during interactions between females. There was some tendency for females to exhibit fewer thanatosis responses on white than on colored backgrounds. Females that were least active had the greatest tendency to exhibit thanatosis.
King, B. H., and J. H. Ellison. 2006. Resource quality affects restlessness in the parasitoid wasp Nasonia vitripennis. Entomologia Experimentalis et Applicata 118:71-76.
Optimal foraging theory, specifically the marginal value theorem, predicts quicker leaving (shorter residence time) from poorer patches. One proximal mechanism for achieving the leaving is that exposure to lower quality resources may trigger increased restlessness (proportion of time in locomotion). Which, if any, aspects of host quality affect restlessness was examined in females of the parasitoid wasp Nasonia vitripennis Walker (Hymenoptera: Pteromalidae). Females were individually exposed to a single host. Restlessness was greater both during and after exposure to a host, when the host was externally damaged vs. intact. Other aspects of host quality that affected restlessness were whether the host was parasitized and whether it was dead and unsuitable for offspring development. In contrast, the hostï¿½s age and stage did not affect restlessness. Increased restlessness did not make females more willing to launch themselves across an inhospitable environment using their wings.<:place><:city>
King, B. H. and Fischer, C. R. 2005. Males mate guard in absentia through extended effects of postcopulatory courtship in the parasitoid wasp Spalangia endius. Journal of Insect Physiology 51:1340-1345.
The proximal mechanisms leading to monandry have been little-studied in most insect orders, including Hymenoptera. In the parasitoid wasp Spalangia endius, mated females are less attractive (less often mounted) than virgins and are unreceptive (unlikely to allow copulation). Which aspects of mating are responsible was tested by observing male responses toward females whose mating had been interrupted at various stages. All females were allowed to receive precopulatory courtship and to open their genital aperture to copulate. Then some were interrupted before copulation; some after copulation but before postcopulatory courtship; and some were allowed to complete postcopulatory courtship. Females that had copulated were not less attractive than females that had not. In contrast, females that had received postcopulatory courtship were clearly both less attractive and less receptive. Thus, postcopulatory courtship functions as extended mate guarding, by making the female less attractive and less receptive to subsequent males even after the original male is no longer present. The effect of postcopulatory courtship on female attractiveness was persistent but imperfect: when males were presented sequentially to mated females, most but not all males retreated without mounting, and a female could repulse more than twenty males in succession.
King, B. H., Saporito, K. B., Ellison, J. H. and Bratzke, R. M. 2005. Unattractiveness of mated females to males in the parasitoid wasp Spalangia endius. Behavioural Ecology and Sociobiology 52:17-24.
Despite common stereotypes, males are not always indiscriminate and eager when it comes to mating. In the parasitoid wasp Spalangia endius, the initial response of males to females was almost always one of apparent excitement; however, this was followed by a clear preference for virgin females over mated females in both no choice and choice situations. The no choice data were collected from videotapes of male-female pairs of all possible combinations of mated and virgin individuals. Neither female nor male mating status had a significant effect on likelihood of, or time until, contact or male courtship fanning. However, a male's first retreat was sooner when the female was mated than when she was virgin; mated males exhibited their first retreat sooner than did virgin males; and mated females were less likely to be mounted than were virgin females. In addition to the videotapes, male choice experiments were performed. When given a choice of a virgin and a mated female, both virgin and mated males were more likely to mount and copulate with the virgin. The difference in response to virgin versus mated females seemed to be less in virgin males than in mated males, perhaps due to virgin males' greater eagerness to mate: when a virgin male and a mated male were presented with a dead virgin female, the virgin male was usually the first to respond to the female. That males preferentially retreated from and avoided mounting mated females appears to be adaptive given that mated females rarely copulated.
King, B. H. and J. A. D'Souza. 2004. Effects of constrained females on offspring sex ratios of Nasonia vitripennis in relation to local mate competition theory. Canadian Journal of Zoology 82:1969-1974.
Empirical studies of how constrained females affect sex ratio are few. Constrained females are those that can produce only sons, e.g., in haplodiploid species, females that have not mated or older females that have used up their sperm. In the parasitoid wasp Nasonia vitripennis ( Walker), failure to mate soon after emergence increased the probability of a female being constrained and thus affected sex ratio directly. Local mate competition (LMC) theory shows that whether a female is constrained can also affect sex ratio indirectly, by affecting what sex ratio other females produce. However, this was not the case in N. vitripennis: a female's sex ratio was not significantly different when she was with another young mated female versus a virgin female or an old mated female depleted of sperm. These results suggest that N. vitripennis females may be unable to recognize whether another female is constrained. The increased proportion of sons in response to other females relative to when alone did not persist the day after exposure.
Olbrich, D. L. and B. H. King. 2003. House fly and stable fly (Diptera: Muscidae) pupae and their parasitoids (Hymenoptera: Pteromalidae) in different habitats on a northern <:state illinois="" dairy="" farm="" great="" lakes="" entomologist="" 36:179-190="" b="">
House fly and stable fly pupae were collected during the summer from a dairy farm in northern Illinois. Spalangia nigroaenea Curtis accounted for most of the parasitoids recovered from house fly pupae. Spalangia nigra Latrielle, S. endius Walker, Muscidifurax spp., and Spalangia nigroaenea accounted for most of the parasitoids from stable fly pupae. House fly pupae accounted for a greater proportion of the fly pupae late in the summer, whereas stable fly pupae accounted for a greater proportion early in the summer. Higher percentages of house flies tended to be in those samples containing lower substrate moisture and higher substrate temperature. Parasitism of stable flies started earlier and peaked weeks before parasitism of house flies, with overall parasitism rates highest from mid to late summer. Parasitism of house flies, but not stable flies, differed significantly among habitats, being greater in calf hutches than in edge samples. Wasps from house flies tended to include a greater percentage of S. nigroaenea (and a lower percentage of Muscidifurax spp.) in calf hutches versus drainage or edge habitats and in substrates consisting of mostly wood shavings versus mostly manure. Within samples, differential parasitism of fly species was not detected for S. nigroaenea, S. endius, or Muscidifurax spp.; but S. nigra differentially parasitized stable flies.
Baeder, J. and B. H. King. 2004. Associative learning of color by males of the parasitoid wasp Nasonia vitripennis (Hymenoptera: Pteromalidae). Journal of Insect Behavior
Males of the parasitoid wasp Nasonia vitripennis showed no innate preference for blue versus yellow or for green versus brown. They learned to associate color with mates, but their ability to do so depended on the color used and the strength of the reward. Specifically, males learned to associate brown or green with a reward of many virgin females. With fewer females, fewer training periods, or mated females as the reward, males still learned a preference for green, but not for brown. Males did not learn to associate color with rewards of honey or water. Previous studies of color preference and associative learning in parasitoid wasps have focussed almost entirely on females. This is the first demonstration of associative learning in response to visual cues by male parasitoid wasps.
King, B. H. 2002. Sex ratio response to conspecifics in a parasitoid wasp: test of a prediction of local mate competition theory and alternative hypotheses. Behavioural Ecology and Sociobiology 52:17-24
Maternal manipulation of offspring sex ratio in response to conspecifics is considered in relation to sex ratio theory using the parasitoid wasp Spalangia endius. Females produced a greater proportion of sons in response to mated but not virgin females. This is the first demonstration of a differential sex ratio response to virgin versus mated females and provides support for local mate competition theory. More recent sex ratio models that predict sex ratio responses to conspecifics, specifically constrained, perturbation, and crowding models, were not supported. An increased proportion of sons in response to another mated female occurred on the second day of oviposition but not on the first, and the day effect resulted from experience not age. When females oviposited alone after 2 d exposure to another female, they still produced a greater proportion of sons than if they had always been alone, but only if the other female was mated, not if she was virgin. Females do not seem to assess the presence of virgin versus mated females indirectly by using a low density of males or a long latency to mate as an indicator for virgin females: neither affected offspring sex ratio. That mated females adjusted their sex ratios in response to other mated females but not virgin females or males may be due proximally to mated females not often encountering the latter. Virgin females and males are not located as deep in the oviposition substrate as mated females.
King, B. H. 2002. Offspring number and sex ratio response to proportion of host sizes and ages in the parasitoid wasp Spalangia cameroni (Hymenoptera: Pteromalidae). Environmental Entomology 31:505-508.
In rearing parasitoids for biological control releases and in natural populations, female parasitoids may encounter variable distributions of host quality. Here I examine how the proportion of hosts that are small versus large or old versus young affects sex ratio and offspring production of the parasitoid wasp Spalangia cameroni Perkins (Hymenoptera: Pteromalidae) parasitizing Musca domestica L pupae. With increasing proportion of small hosts or old hosts, overall number of offspring did not significantly decrease and the overall proportion that were male (i.e., from small and large hosts combined) did not significantly increase. A greater proportion of sons from small versus large and from old versus young hosts was not restricted to the case of equal numbers of different host types. The proportion of sons produced from small hosts as well as the proportion of sons from large hosts decreased as the proportion of small hosts increased, and the proportion of sons produced from young hosts decreased as the proportion of old hosts increased. These results are relevant to recommendations for rearing S. cameroni for biological control releases and to testing evolutionary sex ratio theory, specifically a combined host-quality and local mate competition model.
King, B. H. 2002. Breeding strategies in females of the parasitoid wasp Spalangia endius: effects of mating status and body size. Journal of Insect Behavior 15:181-193.
Does the mating status or body size of a female parasitoid wasp affect her host size choice or propensity to burrow? In Spalangia endius, using smaller hosts appears to reduce a female's cost of parasitization, but not her son's fitness. However, virgin females, which produce only sons, did not preferentially parasitize smaller hosts. Mated females also showed no host size preference. Mated females burrowed more than virgins in the presence of hosts, although not in their absence. Burrowing may reduce a mated female's harassment from males, and not burrowing may increase a virgin female's chance of mating because males avoid burrowing. Mating did not increase female longevity. Greater female size increased offspring production of mated females burrowing for hosts, but not in the absence of burrowing and not in virgin females. A female's size had no significant effect on whether her first drill attempt was on a large or a small host, or on the duration of her successful drills.
King, B. H. 2001. Parasitization site on the host of the parasitoid wasp Spalangia endius (Hymenoptera: Pteromalidae). Environmental Entomology 30:346-349.
Spalangia endius Walker, a parasitoid wasp, parasitizes both young and old Musca domestica pupae, but parasitization site differed with host age. With young hosts, a mother's first drill attempt was about equally likely to be on either half of the host; and host half did not affect the number of drill attempts, the proportion of those attempts that were successful, or the duration of the first successfully completed drill. In contrast, with old hosts, mothers tended to attempt drilling sooner and more often on the posterior versus anterior half of hosts; and a greater proportion of drills were successful on the posterior half. Offspring head width did not differ significantly between offspring oviposited on the posterior versus anterior half of hosts, regardless of host age. Once adult, most offspring chewed out through the anterior half of the host, regardless of host age.
King, B. H. 2000. Sperm depletion and mating behavior in the parasitoid wasp Spalangia cameroni (Hymenoptera: Pteromalidae). The Great Lakes Entomologist 33:117-127.
Mating behavior was examined in the parasitoid wasp Spalangia cameroni. Males attempted copulation with both virgins and already mated females. Males attempted copulation regardless of whether they still had sperm. Already mated females rejected attempts to mate again but virgin females would mate with males regardless of whether or not they had sperm left. Males mated with 12-52 females before exhausting their sperm supplies. Males that had mated only once daily exhausted their sperm supplies in their late thirties (days old), if ever; and males that had mated four times daily exhausted their's at 7-13 days. Males produced as many as 438 daughters from their first four matings. 57% (17 of 30) of females that had mated with virgin males exhibited a decrease in proportion of daughters with age, presumably as a result of sperm depletion. Whether or not a female depleted her sperm supplies was not related to her size or the total number of daughters that she had produced.
Oliai, S.E. and B. H. King. 2000. The associative learning capabilities of the parasitoid wasp, Nasonia vitripennis (Hymenoptera: Pteromalidae). Journal of Insect Behavior 13:55-69.
Abstract. A parasitoid that can learn cues associated with the host microenvironment should have an increased chance of future host location and thereby increase its reproductive success. This study examines associative learning in response to simultaneous exposure to the colors yellow and blue in mated females of the parasitoid wasp Nasonia vitripennis. Preference was measured as the proportion of time spent on a color. When trained with one color rewarded with hosts and honey and the other unrewarded, females showed an increase in preference for the rewarded color with increasing number of training days (1, 3, and 7 days). Hosts and honey together produced a slightly greater preference toward the rewarded color than just hosts, which produced a greater preference than just honey. When trained with a variable reward on one color and a constant reward on the other, females preferred the color associated with the variable reward when it was yellow, but not when it was blue. Thus, relative to no reward, the presence of a variable reward decreased the strength of preference toward the constantly rewarded color. Finally, females trained with regular hosts on one color and used hosts on the other preferred the color associated with the regular hosts when that color was blue but showed no preference in the reverse situation. The presence of used hosts instead of no reward did not increase the strength of preference for the color associated with the regular hosts.
King, B. H. 2000. Sex ratio and oviposition responses to host age and the fitness consequences to mother and offspring in the parasitoid wasp Spalangia endius. Behavioral Ecology and Sociobiology 48:316-320
In the parasitoid wasp Spalangia endius more offspring and a greater proportion of daughters were oviposited in, and emerged from, 0-day-old versus 3-day-old hosts. Offspring that developed on the younger hosts 1) were larger at adulthood, 2) developed more quickly, 3) had higher survivorship to adulthood, and 4) were more often able to chew their way out of the host. Sons and daughters did not differ in how host age affected their size, development rate, or survivorship. The greater proportion of daughters from the younger hosts may be adaptive as described by the host quality model (a variant of the Trivers and Willard hypothesis). It is adaptive if greater size or more rapid development has a more positive effect on daughter's than son's fitness and the positive effect is large enough to compensate for sons being trapped disproportionately to daughters in the older hosts. Despite greater success at drilling the younger hosts, mothers did not try to drill them sooner or more often. Having previously oviposited on the older hosts rather than the younger hosts had no detrimental effect on the mother's subsequent longevity or offspring production.
King BH, Grimm KM, Reno HE. 2000. Effect of mating on the locomotor activity in the parasitoid wasp Nasonia vitripennis (Hymenoptera: Pteromalidae). Environmental Entomology 29(5):927-933
Effect of mating status on locomotor activity was examined in females of the parasitoid wasp Nasonia vitripennis ( Walker). Mated females were more active than virgin females in both strains of N. vitripennis that were tested and regardless of whether or not the mated female stayed with her mate prior to testing. Mated females were more active than virgin females when tested immediately after mating and when tested 1 h, 1.5 h, and 2 h after mating. Mated females were still more active than virgin females when both had been allowed to parasitize a host for 2 h. Mated females were not significantly more active than virgin females at 1, 3 and 5 d after mating. Mated females that were allowed to parasitize a host for 3 h prior to testing were less active compared to those not given a host. Amount of activity was independent of a female's head width and did not affect a female's subsequent offspring production. Despite being more active, mated females did not kill more hosts than virgin females. However, among mated females, females that were more active subsequently killed more hosts, whereas this was not true for virgin females. Discussion of relevance to biological control and suggestions for future research are provided.
Napoleon, M.E., and King, B.H. 1999. Offspring sex ratio response to host size in the parasitoid wasp Spalangia endius. Behavioral Ecology and Sociobiology 46(5): 325-332.
The host size model, an adaptive model for maternal manipulation of offspring sex ratio, was examined for the parasitoid wasp Spalangia endius. In a Florida strain, as the model predicts, daughters emerged from larger hosts than sons, but only when mothers received both small and large hosts simultaneously. The pattern appeared to result from the mother's ovipositional choice and not from differential mortality of the sexes during development. If sex ratio manipulation is adaptive in the Florida strain, it appears to be through a benefit to daughters of developing on large hosts rather than through a benefit to sons of developing on small hosts. Both female and male parasitoids were larger when they developed on larger hosts. For females, developing on a larger host (1) increased offspring production, except for the largest hosts, (2) increased longevity, (3) lengthened development, and (4) had no effect on wing loading. For males, development on a larger host had no effect on any measure of male fitness - mating success, longevity, development duration, or wing loading. In contrast, a strain from showed no difference in the size of hosts from which daughters versus sons emerged, although both female and male parasitoids were larger when they developed on larger hosts. These results together with previous studies of Spalangia reveal no consistent connection between host-size-dependent sex ratio and host-size-dependent parasitoid size among strains of S. endius or among species of Spalangia.
King, B.H. 1998. Host age response in the parasitoid wasp Spalangia cameroni (Hymenoptera: Pteromalidae). Journal of Insect Behaviour 11: 103-117.
Female Spalangia cameroni produced more offspring from younger house fly pupae, both when given a choice of host ages and when not given a choice. Host age did not affect offspring survivorship. Offspring were larger when they had developed on younger hosts and the effect was independent of offspring sex. Having previously parasitized old hosts versus young hosts did not reduce a female's production of offspring in subsequent hosts. Females distinguished between young and old hosts both in the light and in the dark. Females did not distinguish between host ages prior to physical contact with the host but could distinguish by the time they first began exploring a host by tapping it with their antennae; thus, they could distinguish before drilling into a host.
King BH, Crowe ML, Blackmore MD.1998. Effects of leaf age response on oviposition and on offspring fitness in the imported willow leaf beetle Plagiodera versicolora (Coleoptera: hrysomelidae). Journal of Insect Behavior 11:23-36.
Imported willow leaf beetles Plagiodera versicolora oviposit on willow leaves, and both larvae and adults feed on the leaves. In the field, eggs were found on leaves near the center of branchlets, and the number of eggs per cluster was independent of leaf area and position. However, in the laboratory, females chose young leaves over old leaves, for both oviposition and feeding and choice did not rely on information on relative position or size of leaves. Developing on young versus old leaves may provide both advantages and disadvantages. In the laboratory, larvae developed more quickly and attained greater adult weight when fed young versus old leaves, perhaps because of increased mandibular wear of larvae fed old leaves. However, in the field, survival of eggs was lower on young versus old leaves. In the laboratory, rates of cannibalism and survivorship to adulthood did not differ on young versus old leaves.
King, B.H. 1997. Effects of age and burial of house fly (Diptera: Muscidae) pupae on parasitism by Spalangia cameroni and Muscidifurax raptor (Hymenoptera: Pteromalidae). Environmental Entomology 26(2): 410-415.
The parasitoids S. cameroni and M. raptor commonly co-occur in nature and are sometimes released together in efforts to control pest fly populations. Laboratory experiments were conducted to determine how the effectiveness of these wasps in killing house flies (Musca domestica) and producing wasp progeny is affected by the wasp species used, host burial and host age. For effectiveness in killing flies, there was a significant 3-way interaction. S. cameroni alone was consistently more effective than Muscidifurax raptor alone or than the 2 species combined, regardless of host age and burial. However, the greater effectiveness of S. cameroni was most pronounced for buried hosts and among unburied hosts for young hosts. S. cameroni produced offspring regardless of host burial and host age. Host burial significantly decreased production of S. cameroni offspring only when S. cameroni was present and hosts were young. Host burial significantly reduced production of M. raptor offspring in all situations. M. raptor produced fewer offspring from young hosts than from old hosts under all conditions, producing no offspring from young buried hosts. Combining S. cameroni and M. raptor did not increase their effectiveness at killing hosts. Being with the other species versus a conspecific had no significant effect on production of M. raptor offspring and increased production of S. cameroni offspring only from young buried hosts.
King, B.H. 1996. Sex ratio responses to other parasitoid wasps: multiple adaptive explanations. Behavioral Ecology and Sociobiology 39: 367-374.
In an effort to distinguish among adaptive models and to improve our understanding of behavioral mechanisms of sex ratio manipulation, this study examines sex ratio response to other wasps in the solitary parasitoid wasp Spalangia cameroni. Relative to when alone, females produced a greater proportion of sons in the presence of conspecifics, regardless of whether the conspecifics were female or male. In addition, females produced a greater proportion of sons after a day with a conspecific male, and after a day with a conspecific female but only if the females had been ovipositing. Relative to when alone, females did not produce a greater proportion of sons in the presence of females of the confamilial Muscidifurax raptor or in response to hosts that had already been parasitized by a conspecific. A combination of evolutionary models may explain S. cameroni's sex ratios. An increased proportion of sons in response to conspecific females is common among parasitoid wasps and is usually explained by local mate competition (LMC) theory. However, such a response is also consistent with the perturbation model, although not with the constrained females model. The response to conspecific males is not consistent with LMC theory or the perturbation model but is consistent with the constrained females model.
King, B.H. 1996. Fitness effects of sex ratio response to host quality and size in the parasitoid wasp Spalangia cameroni. Behavioral Ecology 7: 35-42.
The parasitoid wasp Spalangia cameroni oviposited a greater proportion of daughters in stable fly pupae than in house fly pupae, even controlling for stable flies being smaller than house flies. Sex ratio manipulation in response to host quality has been modeled as being adaptive through an effect of host quality on the size and hence offspring production of daughters. S. cameroni's response to host species may instead be adaptive through an effect on larval survivorship, the development time of daughters, and the size of sons. There was greater survival of daughters than sons on stable flies. Controlling for host size, development time of daughters was about 2% less on stable flies than on house flies. The decrease in development time corresponds to a 2% increase in fitness as estimated by r, the intrinsic rate of increase, and is equivalent to about a 9% increase in offspring production. Sons were about 2% larger from house flies than stable flies, which may increase offspring production by up to 3%. There was no consistent effect of host species on size of daughters or development time of sons. In addition to the response to host species, mothers oviposited a greater proportion of daughters in larger stable fly hosts. Whether this behavior is adaptive is unclear. Although offspring were larger when they developed on larger stable flies, the rate of increase was less for daughters than for sons. Effects of stable fly size on offspring development time were negligible.
King, B.H. and King, R.B. 1995. Sibmating and its fitness consequences in the parasitoid wasp Spalangia cameroni (Hymenoptera: Pteromalidae). Journal of Insect Behavior 8(5): 723-730.
Spalangia cameroni showed no preference for or against mating with brothers as evidenced by no significant difference in likelihood of mating with brothers versus nonbrothers in the choice experiment and as evidenced by no difference in duration until mounting or duration until mating in either the choice or no choice experiments. There was no evidence that sibmating affected fitness as measured by number of adult offspring. Offspring sex ratio also was unaffected by sibmating.
King, B.H., Crowe, M.L. and Skinner, S.W. 1995. Effect of host density on offspring sex ratios and behavioral interactions between females in the parasitoid wasp Nasonia vitripennis (Hymenoptera: Pteromalidae). Journal of Insect Behavior 8: 89-102.
Pairs of females of the parasitoid wasp Nasonia vitripennis were videotaped with one or two hosts. The presence of an additional host decreased the number of interactions between females but had no measured effect on the nature of the interactions, i.e., on whether the interaction involved physical contact or occurred while one of the females was parasitizing a host. The number of hosts did not itself affect offspring sex ratios but did influence which other factors were correlated with sex ratio. When there was one host, the proportion of sons was more positively correlated with utilization of previously drilled holes than with female-female interactions, whereas when there were two hosts, the reverse was true. Parasitizing an already parasitized host appeared to affect a female's sex ratio beyond any effects of the physical presence of another female: When two hosts were present, the proportion of sons was greater from hosts parasitized by both females than from hosts parasitized by only one female. The observation that parasitizations in previously drilled holes and female-female interactions are correlated with sex ratios is consistent with previous studies; however, that these relationships are host density dependent is a new result and remains unexplained.
King, B.H. 1994. Effects of host size experience on sex ratios in the parasitoid Spalangia cameroni. Animal Behaviour 47(4): 815-820.
The sex ratio response of a female parasitoid wasp Spalangia cameroni is affected both by the size of the host that she is parasitizing and by the size of hosts that she has previously encountered. When given small and large hosts simultaneously, S. cameroni females oviposit a greater proportion of sons in the small hosts (King, 1988, Evolution, 42, 1190-1198). Two hypotheses were tested to examine how a female's offspring sex ratio is affected by her previous host size experience. First, van den Assem et al.'s (1984, Neth. J. Zool., 34, 33-62) life expectancy hypothesis was tested. This hypothesis suggests that when females encounter only small hosts, the production of daughters will be inhibited initially and then, as no large hosts become available, production of daughters will increase. This hypothesis was not supported. The second hypothesis tested was that in their sex ratio responses, females will judge hosts as small or large relative to other hosts encountered. This hypothesis was supported under some conditions. Females judged hosts as small or large relative to previously encountered hosts when parasitizing large hosts and when the previous experience with hosts was immediately prior. When a female received only one host size, females that were given small hosts produced either a greater proportion of sons or the same sex ratio as females that were given large hosts.
King, B.H. 1994. How do female parasitoid wasps assess host size during sex-ratio manipulation? Animal Behaviour 48(3): 511-518.
As in many parasitoid wasps, Spalangia cameroni females oviposit a greater proportion of daughters in large hosts than in small hosts. How females assess host size for this sex-ratio manipulation was examined: do females require visual cues and do they use exposed surface area or volume or duration required to drill into a host prior to oviposition? Visual cues are not necessary; in the dark, females still produced a greater proportion of daughters in large hosts than in small hosts. To examine whether females use exposed surface area or volume to estimate host size, proportion of daughters was compared between unburied hosts and hosts that had been half-buried either horizontally or vertically. Burying hosts did not interfere with host-size assessment for sex-ratio response; sex ratios did not differ between partially buried hosts and unburied hosts of the same size. Females do not appear to use duration required to drill into a host prior to oviposition to assess a host's resources. Drill duration was not consistently longer or shorter for the types of hosts in which daughters versus sons tended to be oviposited. Specifically, a greater proportion of daughters were oviposited in large hosts than in small hosts and in young hosts than in old hosts. Drill duration was longer in large hosts than small hosts but was shorter in young hosts than old hosts. The greater average drill duration observed for daughters suggests that daughters may be more costly to produce than sons.
King, B.H. and Lee, H.E. 1994. Test of the adaptiveness of sex ratio manipulation in a parasitoid wasp. Behavioral Ecology and Sociobiology 35(6): 437-443.
In behavioral ecology it is generally assumed that behavior is adaptive. This assumption is tested here for sex ratio manipulation in response to host size in the parasitoid wasp Spalangia cameroni. Females produce a greater proportion of daughters on larger hosts. If this behavior is adaptive, it is not through a positive effect of host size on the fitness of daughters, as theory suggests and as found for other species. Females that developed on larger hosts were not more successful at drilling into hosts, were not more successful at interspecific competition for hosts, and did not have greater dispersal ability as measured by wing loading (weight/area of wing and thorax). The possibility that S. cameroni's sex ratio manipulation may be adaptive through a negative effect of host size on the fitness of sons cannot be ruled out. Relative to males from larger hosts, males from smaller hosts had lower wing loading and thus potentially greater dispersal ability. The actual effect of wing loading on fitness remains to be tested.
King, B.H. and King, R.B. 1994. Sex ratio manipulation in response to host size in the parasitoid wasp Spalangia cameroni: is it adaptive? Behavioral Ecology 5(4): 448-454.
Many species of parasitoid wasps produce a greater proportion of sons in small than in large hosts. As described by the host-size model, natural selection is becoming a standard explanation for the evolution of this phenomenon. We examined a critical assumption of the host-size model, that host size has a more positive effect on female than on male reproductive success. In laboratory experiments with the parasitoid wasp Spalangia cameroni, females that developed on larger hosts contained more eggs at emergence. However, more eggs did not translate into more offspring, at high or low density and regardless of whether a female had to burrow to reach hosts. The size of host on which a female developed was also unrelated to her longevity, regardless of the presence or absence of hosts. The size of host on which a male developed had no effect on his sperm production or ability to inseminate females, regardless of whether insemination ability was measured by the amount of sperm transferred to a female, by the proportion of a male's mates that produced any daughters, or by the proportion of daughters that a male's mates produced. Thus, despite data on multiple measures of fitness under a range of conditions, sex ratio manipulation in response to host size in S. cameroni does not appear to be adaptive, and another explanation is needed.
King, B.H. 1993. Sex ratio manipulation by parasitoid wasps. pp. 418-441. In: Wrensch DL, Ebbert, M (eds). Evolution and Diversity of Sex Ratio in Insects and Mites. Chapman and Hall, New York.
At least some parasitoid wasp species manipulate offspring sex ratio in response to environmental conditions. Most, but not all, species of parasitoid wasps that have been examined produce a greater proportion of sons in smaller hosts, as predicted by host quality models. The more than forty species meeting this prediction come from thirteen different families and include primarily solitary species, but also some gregarious and facultatively gregarious species. Species meeting the prediction include primarily parasitoids of nongrowing hosts, but also some parasitoids of growing hosts. In addition, most, but not all, species of parasitoid wasps that have been examined produce a greater proportion of sons in the presence of other mothers than when alone, as predicted both by LMC models and by a host quality model for gregarious species. The sixteen species meeting this prediction come from five different families and include both solitary and gregarious species. Most, if not all, of these solitary species parasitize clumped hosts. Differential mortality of the sexes has been ruled out as the cause of the relationships between sex ratio and host size and between sex ratio and number of mothers for nine and nine species respectively. Thus, in these species, mothers are known to be manipulating their offspring sex ratios in response to environmental conditions. In order to understand the evolution of sex ratio manipulation in parasitoid wasps, we need more empirical information regarding constraints on manipulation and the assumptions of models of adaptive manipulation. Insufficient data on the assumptions of sex ratio models and the extent to which limitations on manipulation occur mean that quantitative predictions about sex ratio manipulation are tentative at best. Fortunately, the models' qualitative predictions are somewhat robust to the assumptions and limitations.
King, B.H. 1993. Flight activity in the parasitoid wasp Nasonia vitripennis (Hymenoptera: Pteromalidae). Journal of Insect Behavior 6(3): 313-321.
Flight activity in females of the parasitoid wasp Nasonia vitripennis ( Walker) was examined by measuring still-air tethered flight. There was a large amount of variation among females in flight duration. The longest single flight (with no pauses of more than 5 s) was more than 2 h long. Mating status had a significant and large effect on flight: mated females flew twice as long as virgin females. There also was a slight but significant effect of age on flight, with 3-day-old females being less likely to fly than 1-day-old females. Flight duration was not affected by prior exposure to other females, to honey, or to a low or a high host density.
King, B.H. 1993.Sequence of offspring sex production in the parasitoid wasp, Nasonia vitripennis, in response to unparasitized versus parasitized hosts. Animal Behaviour 45: 1236-1238.
Sequence of offspring sex production differed between the unparasitized and parasitized host treatments. In unparasitized hosts, the proportion of sons that females produced increased with clutch size; whereas in parasitized hosts, the proportion of sons decreased. In unparasitized hosts, the number of daughters increased steadily with increasing clutch size; sons were not produced in clutches of less than four. In contrast, in parasitized hosts, the number of sons increased steadily; daughters were not produced in clutches of less than eight. Offspring sex ratio was more variable in parasitized than in unparasitized hosts.
King, B.H. and Seidl, S.E. 1993. Sex ratio response of the parasitoid wasp Muscidifurax raptor to other females. Oecologia 94(3): 428-433.
This study examines the sex ratio response of the parasitoid wasp Muscidifurax raptor to conspecific and confamilial females in relation to two groups of functional sex ratio models, local mate competition and host quality models. In some but not all experiments, M. raptor females produced a greater proportion of sons in the presence of a conspecific female than when alone, and this sex ratio effect carried over for a day after the females were isolated from each other. M. raptor females also produced a greater proportion of sons in the presence of a female of the confamilial parasitoid Spalangia cameroni than when alone (although only on the second day of exposure to S. cameroni, not on the first). M. raptor's sex ratio increase in the presence of conspecifics is consistent with local mate competition models but not with host quality models because the presence of a conspecific female did not cause there to be more, and thus potentially smaller, offspring developing per host. In contrast, the presence of a S. cameroni female did cause there to be more offspring developing per host than when a M. raptor female was alone; thus, M. raptor's sex ratio increase in the presence of S. cameroni may be explained by host quality models. An alternative explanation for the sex ratio increase in response to confamilials is that only a sex ratio response to conspecifics may be adaptive, due to local mate competition; but M. raptor females may be unable to distinguish between conspecific and S. cameroni females.
Seidl, S.E. and B.H. King. 1993. Sex ratio response to host size in the parasitoid wasp Muscidifurax raptor. Evolution 47:1876-1882.
The proportion of sons produced by M. raptor was greater from small than from large hosts as predicted by the host size model. There was no evidence of differential mortality, suggesting that the greater proportion of sons from small versus large hosts results from maternal manipulation of sex ratio at the time of oviposition. Although the host size model prediction that a greater proportion of sons will be oviposited in small than in large hosts was supported, the model's assumption that host size has a more positive effect on the reproductive success of daughters than sons was not supported. Host size did not affect wasp size. Furthermore, there was no evidence that host size affects either female or male reproductive success. Female M. raptor did not exhibit a positive relationship between host size and longevity or offspring production, regardless of how offspring production was measured. Male M. raptor did not exhibit a positive relationship between host size and longevity or mating success.
King, B.H. 1992. Sex-ratios of the wasp Nasonia vitripennis from self-versus conspecifically-parasitized hosts: local mate competition versus host quality models. Journal of Evolutionary Biology 5(3): 445-455.
Sex ratio patterns in the parasitoid wasp Nasonia vitripennis are frequently cited in support of a major group of evolutionary sex ratio models referred to as local mate competition (LMC) models. It has been shown repeatedly that, as predicted by LMC models, females generally oviposit a greater proportion of sons in previusly parasitized hosts that in unparasitized hosts. However, this sex ratio pattern is also a prediction of another group of sex ratio models, the host quality models. Here I test a prediction of LMC models that is not also a prediction of host quality models: a female should produce a greater proportion of sons when she parasitizes a host previously parasitized by a conspecific female than when she parasitizes a host previously parasitized by herself. Females made this predicted distinction between self- and conspecifically-parasitized hosts under some conditions. There was no evidence that a female recognizes a self-parasitized host when her exposure to the host is interrupted by exposure to an unparasitized host, or that a female can distinguish between hosts parasitized by sisters versus nonsisters.
King, B.H. and Skinner, S.W. 1991. Proximal mechanisms of the sex ratio amd clutch size responses of the wasp Nasonia vitripennis to parasitized hosts. Animal Behaviour 42: 23-32.
Female Nasonia vitripennis lay fewer eggs and increase the proportion of male offspring when ovipositing in hosts that have been previously parasitized compared with unparasitized hosts. This study examines the location and nature of the cues that females use in these clutch size and sex ratio decisions. Neither the sex ratio nor the clutch size response relies on chemical cues on, or a hole drilled in, the outer shell of the host (the puparium). Rather, the cues for both responses appear to be associated with the host pupa. Females manipulate clutch size but not sex ratio in response to host death: the number of eggs laid on dead hosts is significantly lower than on either live hosts or previously parasitized hosts. In addition, the cues that females use for sex ratio manipulation, but not for clutch size manipulation, are local: sex ratio cues are not detected from the end of the host that is opposite the site of parasitization; clutch size cues are. The cues that females use may constrain their sex ratio and clutch size manipulation abilities.
King, B.H. and Skinner, S.W. 1991. Sex ratios in a new species of Nasonia with fully-winged males. Evolution 45: 225-228.
We present results showing that N. giraulti does manipulate offspring sex ratio in response to number of other mothers present, but that N. giraulti produces even more, not less, female-biased sex ratios than N. vitripennis.
King, B.H. 1991. No intersexual differences in host size and species usage in Spalangia endius (Hymenoptera: Pteromalidae). Great Lakes Entomologist 24:17-20.<:place>
Spalangia endius were collected from fly pupae, primarily house fly and stable fly, from a poultry house in Indiana. Male and female wasps did not differ within and across host species in host size usage. Also, despite stable fly pupae being significantly smaller than house fly pupae, the proportion of male wasps emerging from the two host species was similar.
King, B.H. 1991. A field study of host size effects on sex ratio of the parasitoid wasp Spalangia cameroni. American Midland Naturalist 125:10-17.<:place>
I examined aspects of Charnov et al.'s (1981) host-size model for the parasitoid wasp Spalangia cameroni, using collections of fly pupae (hosts) from a poultry house. The model predicts that female parasitoid wasps should emerge from larger hosts than males. This prediction was supported for two collection dates in which only one host species, house flies, was parasitized by S. cameroni. The prediction was not supported either within host species or combining host species for the collection date in which both house flies and stable flies were parasitized. In fact, female S. cameroni emerged from smaller stable fly pupae than did males. The prediction of the host-size model also was not supported on a between host species basis. Though stable fly pupae are significantly smaller than house fly pupae, the sex ratio (proportion of males) of S. cameroni emerging from stable flies was not significantly greater than from house flies. Contrary to expectations, field data showed no positive relationship between host size and female wasp size either within or between host species. Laboratory experiments indicated that female S. cameroni judge host size relative to the size of other hosts encountered, as predicted based on the significant temporal variation found in the host size distribution in the field.
King BH. 1990. Interspecific differences in host (Diptera: Muscidae) size and species usage among parasitoid wasps Hymenoptera: Pteromalidae) in a poultry house. Environmental Entomology 19:1519-1522.
Fly pupae, primarily house fly (Musca domestica Linnaeus) and stable fly (Stomoxys calcitrans (Linnaeus)) (Diptera: Muscidae), were collected from a poultry house in northern Indiana, and parasitoid wasps developing in them were allowed to emerge. Fly pupae density, relative species abundance, and size varied with collection date. Four species of parasitoid wasps were reared from the fly pupae: Spalangia endius Walker, S. cameroni Perkins, S. nigroaenea Curtis, and Muscidifurax raptor Girault and Sanders (Hymenoptera: Pteromalidae). There was some evidence of differential host species and size usage among the wasp species; but the differences were small, and there was considerable overlap. Percent parasitism was independent of host species for S. endius and S. cameroni, but M. raptor emerged from house fly pupae more frequently than expected by chance and from stable fly pupae less frequently than expected. S. endius emerged from larger hosts than did S. cameroni, despite S. endius being on average smaller than S. cameroni. This is the first study to examine host size differences among these parasitoid wasps. '
King BH. 1990. Sex ratio manipulation by the parasitoid wasp Spalangia cameroni in response to host age: a test of the host-size model. Evolutionary Ecology 4:149-156.
A sex ratio response to host resources as measured by external host dimensions has been demonstrated in many parasitoid wasps, including Spalangia cameroni. The responses generally are in the direction predicted by sex ratio theory, specifically the host size models. Here I show that female S. cameroni also respond to differences in resource availability not associated with changes in external host dimensions, and this response is in the direction predicted by host size models. When given old and young hosts simultaneously, female S. cameroni oviposit a greater proportion of sons in old than in young host pupae, at least for 0-day old versus 3-day old hosts. Old hosts weigh less than young hosts but are not significantly different in external width. Thus it appears that the offspring sex ratio response may result from mothers detecting physical or chemical changes within the host which are associated with host age. No evidence is found that the manipulation in response to host age has been selected for via an effect of host age on wasp size: there was no significant effect of host age on either male or female wasp size. A second prediction of the host size models is also supported by this study: when each female is presented with only a single host age, rather than two host ages simultaneously, host age has no effect on offspring sex ratio.
King BH. 1989. Host size-dependent sex ratios among parasitoid wasps: Does host growth matter? Oecologia 78:420-426.
Waage's (1982) hypothesis that host-size-dependent sex ratios will occur in parasitoids of nongrowing hosts and not in parasitoids of growing hosts is examined using published data on parasitoid wasps. Waage's hypothesis is supported as a general, but not absolute, rule: among solitary parasitoid wasps, a significantly greater proportion of parasitoids of nongrowing than of growing hosts show some evidence of host-size-dependent sex ratios (85% versus 45%, G = 5.28, p < 0.05). The premise of Waage's hypothesis--that for parasitoids which develop in a growing stage, host size at oviposition is not a good predictor of the amount of resources available to the developing parasitoid--is also examined. It is suggested that across host species Waage's premise will hold for some, but not all, parasitoids of growing hosts. Likely exceptions to Waage's premise, and thus his prediction, are discussed. Parasitoids of growing hosts which are expected to have evolved host- size-dependent sex ratios include parasitoids which utilize a narrow size range of host species, parasitoids which can distinguish among host species by some criterion other than size, and parasitoids which utilize host species whose susceptible instars do not overlap in size.
King BH. 1989. A test of local mate competition theory with a solitary species of parasitoid wasp, Spalangia cameroni. Oikos 55:50-54.
The effect of conspecific females on offspring sex ratio was examined in the parasitoid wasp Spalangia cameroni. In the presence of a second female, females increased the proportion of sons they produced relative to when they were alone, as predicted by local mate competition theory. However, females did not seem to differentiate between two and more than two females: offspring sex ratios from groups of two, four, six, and ten females were not significantly different. The trace odor of another female was not a sufficient cue for females to increase the proportion of sons they produced. Results indicate that for species with large interfemale variation in offspring sex ratio, it is preferable to test how the presence of other females affects offspring sex ratio by looking for changes within individual females rather than by comparing different-sized groups of females.
King BH. 1988. Sex ratio manipulation in response to host size by the parasitoid wasp Spalangia cameroni: a laboratory study. Evolution 42:1190-1198.
The prediction of Charnov et al.'s (1981) host-size model that there should be a negative relationship between host size and wasp sex ratio (proportion sons) was supported for Spalangia cameroni, a solitary parasitoid wasp. The relationship was shown to be a result of offspring sex manipulation by females in response to host size rather than a result of differential mortality of the sexes. A major assumption of the host-size model is that host size has a greater effect on the ultimate reproductive success of emerging female wasps than of males. This assumption was not supported. Host size had a positive effect on the size of both male and female S. cameroni. However, there was no effect of host size or wasp size on several aspects of reproductive success--production of offspring by females, ability of males to compete for mates, and male and female longevity. Host size may differentially affect the reproductive success of female and male wasps through effects on other aspects of reproductive success. Tests of the assumptions of offspring sex- ratio manipulation hypotheses are scarce but critical, not only for parasitoid wasps, but also for other organisms.
King BH. 1987. Offspring sex ratios in parasitoid wasps. Quarterly Review of Biology 62:367-396.
Laboratory and field studies on about 100 species in sixteen families indicate that several factors can influence offspring sex ratios in parasitoid wasps. For many species, offspring sex ratio increases with one or more of the following: 1) maternal age at ovipositing or the amount of time since insemination, 2) the age of the male parent or the number of times he has copulated, 3) extreme temperature, 4) decreasing host size, age, or quality, 5) female wasp density, and 6) the number of progeny per host. Other factors which have been shown to affect offspring sex ratios in some species include: 1) number of hours since insemination, 2) genetic factors, 3) maternal size, 4) maternal diet, 5) polyembryony, 6) photoperiod and relative humidity, 7) host sex, and 8) host density. These factors may affect offspring sex ratios through females manipulating fertilization of their eggs or through other mechanisms such as differential mortality or changes in sperm availability. Theoretical development has focused primarily on females manipulating their offspring sex ratios in response to host size and/or to female density. Host size models predict a negative relationship between offspring sex ratio and host size. These models assume that host size has a greater effect on the reproductive success of females than of males. LMC models predict a positive relationship between offspring sex ratio and female density. A major assumption of these models is that males mate primarily in their natal area. For each model, most of the species examined meet the model's general prediction. However, the models have been rigorously tested for only a few species. Such testing requires supporting data on the assumptions made and examination of alternative explanations, particularly sex ratio differences due to differential mortality.
Hurlbutt BL. 1987. Sexual size dimorphism in parasitoid wasps. Biological Journal of the Linnean Society 30:63- 89. Sexual dimorphism in body length and proportion of overlap between the ranges of body length for males and females were estimated for 361 species of parasitoid wasp from 21 families. In most species, females are generally larger than males, though the range of male and female sizes overlap. Species in the family Ichneumonidae differ significantly from species in other families in three ways: (1) ichneumonids on average are larger, (2) in most species, females are generally smaller than males, and (3) on average, proportion overlap between the ranges of body length for males and females is greater. At present, there is a paucity of life history data on parasitoid wasp species for which size dimorphism is known. Thus it is not clear why ichneumonids differ among species in other families. Possible evolutionary explanations for variation in dimorphism among parasitoid wasp species are discussed.
Hurlbutt BL. 1987. Sex ratio in a parasitoid wasp, Spalangia cameroni(Hymenoptera: Pteromalidae). Ph.D. dissertation, Purdue University, West Lafayette, Indiana.