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This review summarizes which body parts have taste function in which insect taxa. Evidence of taste by mouthparts, antennae, and tarsi is widespread. Mouthparts that commonly have taste function are the labium, including the labella and labial palps, the maxillae, including the galeae and maxillary palps, the inner surface of the labrum or clypeolabrum of chewers, and inside the precibarium/cibarium of hemipterans, which have piercing-sucking mouthparts. Tasting with mandibles has not been found, and tasting with the hypopharynx is seldom reported. Use of the antennae appears uncommon among fly species, but common among species of lepidopterans, hymenopterans, beetles, and bugs. Although tasting with legs, especially tarsi, is reported mostly for fly and lepidopteran species, there is also evidence of it for multiple species of beetles, grasshoppers, and hemipterans, and one species of a roach, an ant, and a bee. Ovipositor taste function has been supported for some species of flies, lepidopterans, hymenopterans, orthopterans, and odonates. Taste by wings has been much less studied, but has been documented in a few fly species. Taste remains unstudied for any species or any body parts of Archaeognatha, Dermaptera, Mantodea, Mecoptera, Phasmatodea, Megaloptera, Neuroptera, Phthiraptera, Psocoptera, Siphonaptera, as well as Raphidioptera, Strepsiptera, Embioptera, Notoptera, and Zoraptera. Across holometabolous insects, larvae have not often been examined, the exception being some species of lepidopterans, flies, and beetles. Taste studies of antenna and legs are uncommon for even lepidopteran and beetle larvae.

Most parasitoid wasps parasitize herbivorous insects, so nectar from flowers is readily available. However, parasitoid wasps are also an important component of the rich invertebrate communities at livestock facilities in large accumulations of manure, where flowers are largely absent. Little is known about adult parasitoid diet and nutrition in these communities. The present study examined this in Spalangia cameroni Perkins, a pupal parasitoid of filth flies. Like many parasitoid wasps, S. cameroni feed on host fluids, and in the laboratory readily feed on honey or a sucrose solution, which increases their longevity. Here adult longevity in the presence of six potential food sources, bovine manure, sorghum silage, bovine milk, buckwheat inflorescence (Polygonaceae), sweet alyssum inflorescence (Brassicaceae), or dandelion inflorescence (Asteraceae), was compared to that with water or honey. Only parasitoids given buckwheat lived as long as parasitoids given honey, and parasitoids given honey or buckwheat lived longer than parasitoids given water. Parasitoids readily ate buckwheat nectar, avoiding pollen grains. Diet affected the amount of free sugars, glycogen, and lipids in complex ways. Compared to parasitoids that were given just water, parasitoids with access to honey or sucrose had higher sugar and glycogen levels, but not detectably higher lipid levels. Access to buckwheat had no detectable effect on a parasitoid’s free sugar, glycogen, or lipid levels; however, then after 4 d with just water, sugar levels were lower and glycogen levels were higher compared to parasitoids that had been given access to only water the entire time.

Spalangia endius Walker is a parasitoid wasp that is commercially available as a biological control agent for filth fly pests in livestock-rearing operations. Imidacloprid is often used to control these flies. The present study examined the sublethal effect of field-realistic concentrations of imidacloprid on mating behavior, offspring sex ratios, and male preference for virgin females. After exposure to imidacloprid, S. endius females that survived were less likely to mate than control females, which will result in male-biased sex ratios because only mated females can produce daughters. Males did not avoid exposed females, but exposed females were almost always unreceptive. Males that survived exposure to imidacloprid exhibited reduced mating competitiveness against unexposed males. However, if an exposed male mated, his mate’s sex ratio and ability to control flies was unaffected. Exposed males were also still able to discriminate against mated, and thus usually unreceptive, females. Together with previous studies, these results suggest that not only does imidacloprid reduce the ability of S. endius females to survive and parasitize hosts, but when an exposed female does survive and parasitize hosts, she is likely to produce just sons, because of her lack of receptivity. More-male-biased populations of S. endius will decrease their efficacy for fly control. Thus, the use of imidacloprid along with this parasitoid may be financially inefficient for pest management.

Veterinary and medical entomologists who are involved in research on pest control often need to perform dose–response bioassays and analyze the results. This article is meant as a beginner’s guide for doing this and includes instructions for using the free program R for the analyses. The bioassays and analyses are described using previously unpublished data from bioassays on house flies, Musca domestica Linnaeus (Diptera: Muscidae), but can be used on a wide range of pest species. Flies were exposed topically to beta-cyfluthrin, a pyrethroid, or exposed to spinosad or spinetoram in sugar to encourage consumption. LD50 values for beta-cyfluthrin in a susceptible strain were similar regardless of whether mortality was assessed at 24 or 48 h, consistent with it being a relatively quick-acting insecticide. Based on LC50 values, spinetoram was about twice as toxic as spinosad in a susceptible strain, suggesting a benefit to formulating spinetoram for house fly control, although spinetoram was no more toxic than spinosad for a pyrethroid-resistant strain. Results were consistent with previous reports of spinosad exhibiting little cross-resistance. For both spinosad and spinetoram, LC50 values were not greatly different between the pyrethroid-resistant strain and the susceptible strain.

In haplodiploid species, daughter production, but not son production, is sexual, requiring paternal contributions. Females may use male signals to choose a mate with better daughter-production potential, if the choice facilitates her production of adaptive sex ratios, e.g., female-biased sex ratios in systems operating under local mate competition (LMC). In the parasitoid wasp Urolepis rufipes, females preferred pheromone markings from males that had mated once versus multiply, were young rather than old, and were uninfected rather than infected when infection was low, but not when infection was high. Mates of singly-mated males had more female-biased offspring sex ratios than those of multiply-mated males, whereas there was no difference for mates of young versus old males. Thus, female preference for singly-mated males appears to provide indirect fitness benefits. A preference for young males, was not beneficial in the laboratory, but in nature young males may have mated less.

Filth flies cause billions of dollars of losses annually to the animal production industry. Fluralaner is a relatively new pesticide currently sold for control of fleas, ticks, and mites on companion animals and poultry. We examined the efficacy of fluralaner against three species of filth flies. Insecticide-susceptible horn flies and stable flies were tested topically. Fluralaner outperformed permethrin by > 2-fold for the horn flies but underperformed permethrin by > 45-fold for stable flies at 24 h. House flies were tested topically with fluralaner in comparison to permethrin at 48 h and orally with fluralaner in comparison to imidacloprid at 24 h. Topical fluralaner was 6- to 28-fold as toxic as permethrin in four pyrethroid-resistant strains and not significantly less toxic than permethrin in a susceptible strain and a mildly pyrethroid-resistant strain. There was slight cross-resistance between topically applied fluralaner and permethrin in all five insecticide-resistant strains tested. Oral fluralaner was more toxic than imidacloprid in all four house fly strains tested, 9- to 118-fold as toxic. Oral cross-resistance between imidacloprid and fluralaner was not detected, but imidacloprid resistance was not high in any of the tested strains. Fluralaner shows promise for control of horn flies and house flies.

Filth flies, including house flies, Musca domestica L., develop in animal manure. Adult house flies often are controlled with pesticides such as imidacloprid. How imidacloprid disseminates and persists after it contaminates manure was measured at a dairy farm. A week after application of imidacloprid via fly bait to cattle manure, a mean of approximately 4 ppm of imidacloprid, and as high as 15 ppm, was quantifiable up to 12 cm from the application site, but not farther. Laboratory experiments addressed the impact of 15 ppm of imidacloprid in manure on egg-to-adult development of house flies and on the biological control ability of a house fly pupal parasitoid, Spalangia endius Walker. In uncontaminated manure, 93% of eggs developed to adults, versus 7% in contaminated manure. In the parasitoid experiment, fly pupae were placed in contaminated or uncontaminated manure with or without S. endius. In the absence of S. endius, nearly 100% of flies emerged, with or without imidacloprid. In the presence of S. endius, only 11% of flies emerged from uncontaminated manure, versus 36% from contaminated manure; and parasitoids emerged from 82% of hosts in uncontaminated manure versus 53% in contaminated manure. These results suggest that realistic concentrations of imidacloprid in filth fly breeding habitat may interfere with house flies developing to the pupal stage, but also with parasitoids locating and utilizing house flies. However, after 1 wk, the effects on parasitoids will be low 12 cm beyond where bait was applied.

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.

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.

Foreign materials like insecticides may increase grooming in insects; and generally, grooming may be expected to reduce effects of insecticides, but this may not be the case when grooming involves the mouth and hence a risk of ingestion. To examine this, female Spalangia endius, a wasp that parasitizes filth fly pupae, were exposed to a surface coated with a low concentration of imidacloprid or not. Their mouthparts were sealed or not to determine whether sealing is a useful method for examining effects of mouth grooming. Wasps mouth-groomed more frequently while exposed to imidacloprid than when not. However, imidacloprid did not increase the number of times that a wasp groomed the rest of her body, and this was true regardless of whether or not her mouthparts were sealed. While exposed to imidacloprid, wasps spent less time locomoting only if their mouthparts were not sealed. Having been exposed to imidacloprid also decreased subsequent longevity, from 9 to 7 d. These effects of imidacloprid on grooming, locomotion, and longevity occurred despite exposure being for just 5 min and to only 2% of the amount that will be present in an area immediately after house fly baits are scattered at their recommended coverage. This is such a low amount that, with 48 h of constant exposure, mortality of these wasps is only 10%. Having mouthparts sealed decreased locomotion and longevity regardless of exposure to imidacloprid. Thus, sealing mouthparts is not useful for measuring effects of mouth grooming.

Use of insecticidal baits risks the evolution of resistance to the feeding stimulant in the bait, not just to the active ingredient (toxicant). Sucrose-based baits are widely used against house flies, Musca domestica L. The baits are applied as dry granules, but readily liquefy. The proboscis extension reflex (PER) and consumption of alternative sweeteners, dry or in solution, were examined. Fructose, glucose, and xylitol merit further study as alternatives to sucrose. Dry, fructose, glucose, and xylitol elicited PER much more than sucrose, although not when in solution. Furthermore, dry or in solution, females and males ate as much or more fructose as sucrose. In solution, flies ate as much glucose as sucrose; although when dry, consumption was much less for glucose than sucrose. Dry, xylitol elicited as much consumption as sucrose for females, though less for males. In solution, for both sexes, xylitol elicited less consumption than sucrose did. Acesulfame potassium, sodium cyclamate, and sucralose do not look promising as they did not often elicit PER, whether dry or in solution. Erythritol also does not look promising. Erythritol elicited PER no more than sucrose did when dry and elicited PER much less than sucrose when in solution. Flies ate much less erythritol than sucrose whether dry or in solution.

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.

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.

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 the three active ingredients (AI): Golden Malrin (methomyl), QuickBayt (imidacloprid), or Quikstrike (dinotefuran). Behavioral responses to each of the two components of the baits, the AIs and the fly attractant pheromone (Z)-9-tricosene, were also examined independently. Spalangia 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. Spalangia 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. Urolepis 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.

Both the parasitoid wasp Spalangia endius Walker and the insecticide imidacloprid are used to control house flies. A recent study found that negative sublethal effects of imidacloprid on killing flies and on offspring production by this parasitoid wasp are eliminated when females have the opportunity to crawl through decaying matter. An enzyme-linked immunosorbent assay showed that the presence of decaying matter reduces the amount of pesticide on their bodies. This study examined whether this was also true for sublethal effects on mating. S. endius were exposed to a realistic concentration of imidacloprid that induces very low mortality. Then, individual parasitoids were allowed to burrow through decaying organic matter or not, followed by mating tests in the absence of decaying matter. Even after 24 h with the decaying matter, copulation for both males and females that had previously been exposed to imidacloprid was delayed compared with no-pesticide controls. Furthermore, for pesticide-exposed males, subsequently burrowing through media made copulation even more delayed than if they were not exposed to media. For pesticide-exposed females, subsequently burrowing through media neither increased or decreased the negative effect of the pesticide exposure. Together with other studies, these results reinforce that use of S. endius and use of imidacloprid are incompatible, even at much lower than recommended concentration, unless application is sufficiently separated in place and time.

The parasitoid wasps Spalangia endius Walker, Spalangia nigroaenea Curtis, and Spalangia nigra Latrielle (Hymenoptera: Pteromalidae) develop on filth fly pupae. Females burrow through decaying organic matter and parasitize hosts; whereas, at least in S. endius, males tend to stay above ground searching for mates. Both sexes lack obvious digging morphology such as enlarged forelegs and are not known to exhibit physical aggression. Size data were obtained from specimens from Illinois field-collected hosts for all three species and from a Florida laboratory colony for S. endius. The degree of sexual size dimorphism varied with body part and species, but the direction of bias was consistent between the field and laboratory specimens of S. endius. Females had wider abdomens in S. nigroaenea and S. nigra (not measured in S. endius). In all three species, females had longer heads than males, both in absolute size and relative to width. The latter is referred to as narrowness. Forewings were significantly narrower in females compared with in males for both S. endius and S. nigroaenea. Thorax narrowness was either greater in males (S. endius) or was not significantly different between the sexes (S. nigroaenea and S. nigra). Patterns of sexual size dimorphism seem consistent with females’ need to store eggs and burrow. For all three species, there was overlap between males and females in all body parts measured. Thus, these size measurements will be unreliable to differentiate the sexes. Size ratios also overlapped.

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. Mating frequency varies widely among animals. In most of the more than 100 past studies of insect species in which females mate multiply, females benefit from remating. However, this same question has been addressed in few species in which females mate just once. In the tiny parasitic wasp studied here, females were tricked into remating. Females benefited from remating if their first mate had previously mated multiple times. The benefit was not producing more offspring, but rather being able to produce a greater proportion of daughters. Sons can be produced without sperm in wasps and wasp relatives. Explanations for why females do not normally remate include that they have been manipulated by their first mate and that waiting for a male means sacrificing searching for hosts.

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>inotefuran>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.

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.

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.

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.

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 2 wk. 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 2 wk 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.

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.

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.

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.

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 females had begun producing only sons by their tenth day, whereas first 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.

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 a confamilial. However, male S. endius did not respond to antennal folding: males did not contact the female's 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 female's abdomen and appeared to detect receptivity directly from the female's abdomen rising as her genital orifice opened. On females whose abdomens did not rise, initiation of male copulation attempts were delayed but 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.

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.

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 of sons. The assumption has often been tested indirectly by examining the 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 L., 1758. If the method is valid, effects of parasitoid size on fitness should match the effects of host size on fitness that were shown in a previous study. The effects matched in that both parasitoid size and host size affected the fitness of females but not of 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.

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 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.

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.

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.

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 focused almost entirely on females. This is the first demonstration of associative learning in response to visual cues by male parasitoid wasps.

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.

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 days' 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.

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 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.

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 the 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.

Spalangia endius Walker, a parasitoid wasp, parasitizes both young and old Musca domestica L. 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.

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 before 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 before testing were less active compared with 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.

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.

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 India 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.

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 the 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 a 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.

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.

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 fewer parasitoids compared with 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 with 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.

The parasitoid wasps Spalangia cameroni Perkins and Muscidifurax raptor Girault & Sanders 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 L., and producing wasp progeny is affected by the wasp specie(s) 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 M. 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.

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 responses 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.

Pairs of females of the parasitoid waspNasonia 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.