Striking cuticular hydrocarbon dimorphism in the mason wasp Odynerus spinipes and its possible evolutionary cause (Hymenoptera: Chrysididae,Vespidae)

Cleptoparasitic wasps and bees smuggle their eggs into the nest of a host organism. Here the larvae of the cleptoparasite feed upon the food provision intended for the offspring of the host. As cleptoparasitism incurs a loss of fitness for the host organism (offspring of the host fail to develop), hosts of cleptoparasites are expected to exploit cues that alert them to potential cleptoparasite infestation. Cuticular hydrocarbons (CHCs) could serve as such cues, as insects inevitably leave traces of them behind when entering a nest. By mimicking the host''s CHC profile, cleptoparasites can conceal their presence and evade detection by their host. Previous studies have provided evidence of cleptoparasites mimicking their host''s CHC profile. However, the impact of this strategy on the evolution of the host''s CHC profile has remained unexplored. Here, we present results from our investigation of a host–cleptoparasite system consisting of a single mason wasp species that serves syntopically as the host to three cuckoo wasp species. We found that the spiny mason wasp (Odynerus spinipes) is able to express two substantially different CHC profiles, each of which is seemingly mimicked by a cleptoparasitic cuckoo wasp (i.e. Chrysis mediata and Pseudospinolia neglecta). The CHC profile of the third cuckoo wasp (Chrysis viridula), a species not expected to benefit from mimicking its host''s CHC profile because of its particular oviposition strategy, differs from the two CHC profiles of its host. Our results corroborate the idea that the similarity of the CHC profiles between cleptoparasitic cuckoo wasps and their hosts are the result of chemical mimicry. They further suggest that cleptoparasites may represent a hitherto unappreciated force that drives the evolution of their hosts'' CHCs.     

Life histories of two ichneumonid parasitoids of Cyclosa octotuberculata (Araneae): Reclinervellus tuberculatus (Uchida) and its new sympatric congener (Hymenoptera: Ichneumonidae: Pimplinae)

In Japan, two species of the genus Reclinervellus were found to attack a single host spider, Cyclosa octotuberculata (Araneae). One of these, Reclinervellus tuberculatus comb. nov., winters as a tender larva and has at least two generations a year. This species laid its egg on the anterior face of the host's abdomen. Prior to laying an egg the female repeatedly rubbed her ovipositor over the dorsal and lateral surfaces of the host's abdomen near the base for more than 25 min. The hatched larva fixed itself at the position where the egg was laid, and developed by consuming the host's body fluids. The other species, R. masumotoi sp. nov., is closely related to R. tuberculatus but is easily distinguished from it by having a very weakly reclivous Cu vein in the hindwing, a less developed carina of the propodeum, a shorter ovipositor and more blackish coloration of the mesoscutum. Although this species is sympatric with R. tuberculatus and attacks the same host, the position of the egg and larva on the host's body is quite different from that of R. tuberculatus. The egg of this species was laid on the posterior surface of the host's abdomen and the larva matured 10–20 days earlier than those of R. tuberculatus. Via these modes of parasitism R. masumotoi seemed to escape from competition with R. tuberculatus at the stage of oviposition and out‐competed it when a single host individual bore larvae of both species. Previous records of parasitoids reared from C. octotuberculata were reviewed and found to include records of both species.     

Water mite parasitism in damselflies during emergence: two hosts, one pattern

The infections of emerging damselfly cohorts by ectoparasitic water mites Arrenurus cuspidator were followed closely over two years in two populations. In one pond Coenagrion puella was the single host species, whereas in the second pond C. hastulatum co-occurred. The prevalences found were close to 100%. The mean daily abundance of mites ranged from I to 45 mites per host with a peak after roughly one third of the emergence period.
The water mites displayed a clumped distribution on their hosts measured by the variance/mean ratio. No differences in parasite abundance due to host sex, head width, or host species could be detected. The abundance of mites was synchronised with host's emergence patterns. This was stronger in the system with two host species. Shaw and Dobson recently showed a generalised relationship of variance/mean of parasite abundance combining data from 269 host parasite systems. The data presented here and some other water mite associations show a significant deviation from this general rule.     

Host sex preferences and transmission success by the water mite Unionicola foili (Acari: Unionicolidae) parasitic on the midge Chironomus tentans (Diptera: Chironomidae)

This study examined whether ecoparasitic larval Unionicola foili exhibited a sex bias when infecting laboratory populations of the host insect Chironomus tentans and whether an association with male or female midges increased the likelihood of larval mites returning to the aquatic habitat. When laboratory populations of C. tentans were exposed to larval U. foili, there was a higher prevalence of mites among female hosts at emergence (17 of 30 males vs. 25 of 30 females infected by mites). However, there was no significant difference in the distribution or abundance of larvae among infected male (mean = 2.3 larvae per host) and female (mean = 2.6 larvae per host) midges. Larval mites parasitizing both male and female chironomids were more likely to return to water than could be expected by chance. Mite larvae infesting female C. tentans were more likely to return to water when female hosts deposited egg masses in water, suggesting that oviposition plays an important role in cueing larvae parasitizing female midges to detach. The mechanism responsible for increasing the likelihood that mites parasitizing male hosts return to water remains unclear. Future studies will address the possibility of parasite-mediated changes in host behavior.     

Hypersensitivity,resulting from host-unsuitability,as exemplified by two parasite species attackingSpodoptera littoralis [Lepidoptera: Noctuidae]

Spodoptera littoralis Boisd. is an unsuitable host for 2 parasite species,Bracon hebetor Say andPalexorista laxa. (Curran).B. hebetor is an exernal parasite that paralyzes its hosts prior to oviposition. In the case ofS. littoralis, parasitization often causes death rather than paralysis and consequently the parasite is unable to reach maturity. The death is not caused by the feeding of the parasite larvae.P. laxa is an internal parasite ofHeliothis spp. that oviposits readily onS. littoralis, but fails to develop therein. It was suggested that the untimely death of the hosts with their parasites prevents control of the former's population by the latter's and, therefore, may be compared to the phytopathological phenomenon of hypersensitivity.     

Reproductive Biology and Behavior of <Emphasis Type="Italic">Tranosema rostrale</Emphasis> (Hymenoptera: Ichneumonidae), a Parasitoid of Low-Density Spruce Budworm (Lepidoptera: Tortricidae) Populations

Tranosema rostrale (Brischke) (Hymenoptera: Ichneumonidae) is an important parasitoid of low-density spruce budworm Choristoneura fumiferana (Clemens) (Lepidoptera: Tortricidae) populations. To investigate the effectiveness of this parasitoid in attacking low-density spruce budworm populations, we conducted a detailed laboratory study on its reproductive biology and behavior including mating behavior, potential fecundity, longevity, host searching, and oviposition behavior. We found that the occurrence of mating increases with the number of males present in the cage but that it drastically decreases when females mated previously. Females may mate multiple times with different males in one breeding session and mating duration is significantly longer when a male mates the second time with the same female. Dissections of T. rostrale’s oviducts showed that it is a synovigenic species emerging with about 17 % of its lifetime egg load and develops most of its eggs in the first three days after emergence at 20 °C. Sugar, but not pollen, significantly increased the insect’s longevity compared to water. Spruce budworm larvae, silk from larvae and damaged balsam fir foliage triggered probing in T. rostrale females significantly more often than larval feces. The sequence of the parasitoid’s behaviors leading to successful attack is described as antennation, probing, insertion of the ovipositor, oviposition, and subsequent disinterest or resuming of the sequence. Defense mechanisms of the host larva such as vigorous movements, biting, and/or regurgitation and behavioral countermeasures by T. rostrale are described in detail.     

Ectoparasites do not affect ejaculate volume in the dragonfly Coenagrion puella

Abstract. Imagoes of the dragonfly Coenagrion puella are parasitized frequently by ectoparasitic water mites. In an experimental study of the parasite load we examined the influence of parasite burden on host sperm volume. Infection with ectoparasitic water mites did not affect sperm volume in the seminal vesicle (ejaculate volume). It is concluded that water mite parasitism does not affect male fitness in C. puella by reducing sperm production.     

Explaining Susceptibility and Resistance to a Multi-Host Parasite

Closely related host species are known to show variation in the level of resistance towards the same or similar parasite species, but this phenomenon is understudied. Such studies are important for understanding the ecological factors that might promote susceptibility or resistance to parasites: in particular, whether one host species is a larger target of selection for the parasite by virtue of being more abundant locally or more regionally widespread than another host species. In this study, we examined the expression of resistance by two closely related species of damselflies (Nehalennia irene and Nehalennia gracilis) against an Arrenurus water mite species. We show that the host species at each of two isolated sphagnum bogs have statistically indistinguishable levels of prevalence and intensity of infection by mite larvae. Despite having similar measures of parasitism, the regionally less represented species (N. gracilis) showed total resistance, whereas the regionally well-represented species (N. irene) was completely susceptible. Moreover, the form of resistance expressed by N. gracilis was unique, in that the oral glands of the mite were melanised. Also, this mite species was not found outside of isolated bog habitats. These results suggest that there might have been strong historical selection from this mite on the bog specialist, N. gracilis, and that this selection may have resulted in resistance evolving to fixation in a series of isolated populations.     

Influence of oviposition strategy of Nemorilla pyste and Nilea erecta (Diptera: Tachinidae) on parasitoid fertility and host mortality

This study examined fertility of the tachinid (Diptera) parasitoids Nemorilla pyste (Walker) and Nilea erecta (Coquillett), and mortality of the host, Choristoneura rosaceana (Harris) (Lepidoptera: Tortricidae). These are common parasitoids of mature C. rosaceana larvae in apple and sweet cherry orchards in central Washington where C. rosaceana is an important pest. The parasitoids have similar phenology and use the same stages of the host, but their modes of attack and development in the host differ. N. pyste oviposits on the host and develops gregariously, while N. erecta ovolarviposits on foliage near the host and develops solitarily. Life tables were used to compare adult longevity and fertility of these flies at three different host densities in laboratory cage experiments. Results suggested that although population growth rates of these species were similar under the experimental conditions, N. erecta had a greater effect on mortality of the host population. This additional mortality was attributed to superparasitism because it occurred in host larvae at a higher rate than expected from natural causes, and it occurred more frequently when fewer hosts were available to N. erecta females. A supplemental experiment demonstrated that host larvae that were manually infected with N. erecta maggots to simulate superparasitism expressed high rates of larval mortality. Thus, even though N. erecta had a greater effect on the host population, reproductive opportunity was lost to superparasitism. These findings may demonstrate certain situational disadvantages of ovolarviposition as a reproductive strategy, and illustrate how parasitism effects may be underestimated in field sampling.     

Biology and behavior of Metaphycus angustifrons Compere (Hymenoptera: Encyrtidae), a newly discovered parasitoid of soft scale insects (Hemiptera: Coccidae) in California

Metaphycus angustifrons Compere has recently been found to be the most abundant parasitoid of brown soft scale, Coccus hesperidum L., in southern California. In laboratory experiments we examined several biological parameters of this species. M. angustifrons both oviposits and host feeds in brown soft scale and is a facultatively gregarious endoparasitoid of this soft scale insect. In contrast with other Metaphycus spp., M. angustifrons is a koinobiont parasitoid, allowing its host to grow up to 40% beyond its size at parasitism. Despite its high abundance on brown soft scale in the field, in the laboratory, high rates of parasitoid egg encapsulation are observed; about half of parasitized hosts failed to issue parasitoids. Furthermore, host scales that encapsulated parasitoids eggs showed significant reduction in development. Increased scale size at oviposition influences the size of emerging females but not the size of males. Female M. angustifrons are synovigenic. They emerge from their hosts without mature eggs and begin maturing eggs after they are provided a carbohydrate source. Carbohydrates prolong the life span of both female and male M. angustifrons. The size of female wasps influences egg load but not longevity. Finally, based on laboratory observations, M. angustifrons uses citricola scale almost exclusively for host feeding and not for oviposition. These results suggest that the role of this species in citricola scale’s decline in southern California in the 1950s–1960s was negligible.     

Stimuli inducing detachment of larvalArrenurus danbyensis (Hydrachnidia: Arrenuridae) from adultCoquillettidia perturbans (Diptera: Culicidae)

In this study, potential cues for detachment of parasitic larvalArrenurus danbyensis Mullen mites fromCoquillettidia perturbans (Walker) mosquitoes were investigated. Contact with water did not induce a dramatic rate of dissociation. Crushing the host's abdomen was not as effective as crushing the head or thorax; although general body trauma has an effect, it is not sufficient to explain these results. Crushing the host's head following application of a ligature slowed the rate of mite detachment. We infer that haemolymph-borne cues, possibly hormones, are released by crushing the head or thorax of the host and induce rapid mite detachment. External application of Ringers solution or body fluids from mosquitoes significantly increased rate of mite detachment. It is possible that two separate mechanisms stimulate detachment of mites: external haemolymph reception signifying damage to the host and internal reception of haemolymph-borne cues associated with oviposition behavior.     

Density dependence of Anaphes sordidatus (Hymenoptera: Mymaridae) parasitism on eggs of Listronotus oregonensis (Coleoptera: Curculionidae)

Listronotus oregonensis (LeConte) (Coleoptera: Curculionidae) oviposits in carrot leaves and the larvae feed in carrot roots. Its eggs are parasitized by Anaphes sordidatus (Girault) (Hymenoptera: Mymaridae) throughout its oviposition period. This parasitoid is the major biotic mortality factor for L. oregonensis. Parasitism by A. sordidatus was studied for three years in sequentially sown plots of carrots, Daucus carota var. sativa. Over the scason, significantly fewer L. oregonensis eggs were oviposited in later sown carrots than in earlier sown carrots because oviposition started later in late sown plots of carrots. A positive temporal density-dependent relationship was observed each year between parasitism rates and host densities. This positive density dependence occurred in early and mid-summer for earlysown carrots where host density reached 1–2 host eggs per plant but disappeared in late summer when host density decreased while parasitism remained high. Latesown carrots had low host egg density (0.2 host egg per plant) and contributed little to the total number of eggs. In these late sown plots, parasitism increased rapidly to over 80% but no density dependence was observed. Spatially, few statistically significant regressions were found but all indicated a positive spatial density-dependence. Most non-significant regressions occurred because the range of egg density was too small between plots for a given date.     

The embryonic development of the marine caddis fly. Philanisus plebeius Walker (Trichoptera: Chathamidae)

1. P. plebeius, a trichopteran with marine intertidal larvae, oviposits in the coelom of a starfish, Patiriella exigua. Oviposition occurs mainly in the spring and autumn months. 2. In spite of the intracoelomic location of the embryos, the development of P. plebeius follows an unmodified trichopteran mode, including the characteristic blastokinesis. Nutrients are not supplied to the caddis embryos by the host starfish. 3. Hatching takes place in the starfish coelum after 17-18 days. The newly hatched caddis larvae quickly escape to their rock pool habitat. 4. The form of the female ovipositor indicates that other species of Chathamidae utilize starfish species as oviposition hosts. 5. This mode of oviposition offers protection to the caddis embryos in the intertidal habitat.     

Linkages between nectaring and oviposition preferences of Manduca sexta on two co‐blooming Datura species in the Sonoran Desert

1. The oviposition choices of phytophagous insects determine the environment that their offspring will experience, affecting both larval performance and host plant fitness. These choices, however, may be influenced by other activities, such as nectar foraging. 2. In the Sonoran Desert, Manduca sexta (Lepidoptera: Sphingidae) oviposits primarily on the perennial herb Datura wrightii. It has been reported to oviposit on the smaller‐flowered, co‐blooming, sympatric annual Datura discolor as well. Datura is also M. sexta's most important source of nectar in this region. Nectaring and oviposition decisions thus determine M. sexta's reproductive success, as well as the relative benefits (pollination) and costs (herbivory) that each Datura species derives from this interaction. 3. The nectaring and oviposition choices of adult M. sexta on these congeners were studied to investigate how nectar foraging influences oviposition. Larval performance on the two hosts was then assessed. 4. Nectaring and oviposition were behaviourally linked, with M. sexta preferring the perennial D. wrightii as both a nectar source and larval host when given a choice between the two species. This preference disappeared, however, when only D. discolor bore flowers. 5. In the laboratory, larvae developed at equal rates when fed D. wrightii or D. discolor leaves, but survival was higher on D. wrightii when larvae fed on intact plants. 6. These findings suggest that while female preferences match larval performance in most cases, the link between nectaring and oviposition may at times bias moths to lay eggs on inferior larval hosts.     

Larviposition of Compsilura concinnata (meigen) (diptera: Tachinidae), a parasitoid of the gypsy moth,Lymantria dispar (L.) (lepidoptera: Lymantriidae)

Larviposition of Compsilura concinnata, a polyphagous tachinid parasitoid of Lepidoptera, is described. The conventional assessment, long‐established in the literature, places the site of larval deposition by C. concinnata as directly into the host's gut. New evidence, reported here, contradicts the earlier view. Dissection of 38 freshly parasitized gypsy moth (Lymantria dispar) larvae revealed as many maggots (n = 26) situated in the lumen of the midgut as were free in the hemocoel. Observations on maggot behavior and morphology in dissected hosts are briefly presented.     

Importance of contact chemical cues in host recognition and acceptance by the braconid larval endoparasitoids Cotesia sesamiae and Cotesia flavipes

The ability of the congeneric braconid parasitoids Cotesia sesamiae (Cameron) and Cotesia flavipes Cameron to discriminate between stemborer larval cues upon contact was studied using their natural hosts, namely the noctuid Busseola fusca (Fuller) and the crambid Chilo partellus (Swinhoe), respectively, and the pyralid non-host Eldana saccharina (Walker). When the natural host larvae were washed in distilled water, parasitoid behavior was similar to that displayed when in contact with E. saccharina, characterized by the absence of ovipositor insertion. When washed host or non-host larvae were bathed with water extracts of their natural host, the parasitoids showed a significant increase in ovipositor insertions. However, the water extracts of host-larvae deposited on cotton wool balls did not induce ovipositor insertion in either C. sesamiae or C. flavipes. Nevertheless, the extracts enabled the parasitoids to discriminate between natural and non-hosts as indicated by the intensive antennating of the former. For both parasitoids, frass was found to be important in short-range host recognition as indicated by differences in the time spent on antennating between frass sources. In addition, the regurgitants of B. fusca and C. partellus induced ovipositor insertion in C. flavipes only. These results indicated that C. sesamiae and C. flavipes used different chemical cues for acceptation and oviposition in a stemborer larva, and that B. fusca and C. partellus shared the same chemical cues to induce oviposition in C. flavipes.     

Attracted to the enemy: Aedes aegypti prefers oviposition sites with predator-killed conspecifics

Oviposition habitat choices of species with aquatic larvae are expected to be influenced by both offspring risk of mortality due to predation, and offspring growth potential. Aquatic predators may indirectly influence growth potential for prey by reducing prey density and, for filter-feeding prey, by increasing bacterial food for prey via added organic matter (feces, partially eaten victims), creating the potential for interactive effects on oviposition choices. We tested the hypothesis that the mosquito Aedes aegypti preferentially oviposits in habitats with predatory Toxorhynchites larvae because of indirect effects of predation on chemical cues indicating bacterial abundance. We predicted that A. aegypti would avoid oviposition in sites with Toxorhynchites, but prefer to oviposit where bacterial food for larvae is abundant, and that predation by Toxorhynchites would increase bacterial abundances. Gravid A. aegypti were offered paired oviposition sites representing choices among: predator presence; the act of predation; conspecific density; dead conspecific larvae; and bacterial activity. A. aegypti preferentially oviposited in sites with Toxorhynchites theobaldi predation, and with killed conspecific larvae, but failed to detect preferences for other treatments. The antibiotic tetracycline eliminated the strongest oviposition preference. Both predation by Toxorhynchites and killed larvae increased bacterial abundances, suggesting that oviposition attraction is cued by bacteria. Our results show the potential for indirect effects, like trophic cascades, to influence oviposition choices and community composition in aquatic systems. Our results suggest that predators like Toxorhynchites may be doubly beneficial as biocontrol agents because of the attraction of ovipositing mosquitoes to bacterial by-products of Toxorhynchites feeding.     

The ectoparasitic wasp Nasonia vitripennis (Walker) (Hymenoptera: Pteromalidae) differentially affects cells mediating the immune response of its flesh fly host,Sarcophaga bullata Parker (Diptera: Sarcophagidae)

In this study, we examined cellular immune responses in the flesh fly, Sarcophaga bullata, when parasitized by the ectoparasitoid Nasonia vitripennis. In unparasitized, young pharate adults and third instar, wandering larvae of S. bullata, four main hemocyte types were identified by light microscopy: plasmatocytes, granular cells, oenocytoids, and pro-hemocytes. Parasitism of young pharate adults had a differential effect on host hemocytes; oenocytoids and pro-hemocytes appeared to be unaltered by parasitism, whereas adhesion and spreading behavior were completely inhibited in plasmatocytes and granular cells by 60 min after oviposition. The suppression of spreading behavior in granular cells lasted the duration of parasitism. Plasmatocytes were found to decline significantly during the first hour after parasitism and this drop was attributed to cell death. Melanization and clotting of host hemolymph did not occur in parasitized flies, or the onset of both events was retarded by several hours in comparison to unparasitized pharate adults. Hemocytes from envenomated flies were altered in nearly identical fashion to that observed for natural parasitism; the total number of circulating hemocytes declined sharply by 60 min post-envenomation, the number of plasmatocytes declined but not granular cells, and the ability of plasmatocytes and granular cells to spread when cultured in vitro was abolished within 1 h. As with parasitized hosts, the decrease in plasmatocytes was due to cell death, and inhibition of spreading lasted until the host died. Isolated crude venom also blocked adhesion and spreading of these hemocyte types in vitro. Thus, it appears that maternally derived venom disrupts host immune responses almost immediately following oviposition and the inhibition is permanent. The possibility that this ectoparasite disables host defenses to afford protection to feeding larvae and adult females is discussed.     

Olfactory host location and learning in the granary weevil parasitoidLariophagus distinguendus (Hymenoptera: Pteromalidae)

The sources of volatiles that attract the parasitoid Lariophagus distinguendus(Först.) to its hosts, the larvae of the granary weevil Sitophilus granarius(L.) infesting grains of Triticum aestivumL., were investigated in bioassays. The influence of oviposition experience on the responsiveness of the parasitoids to the sources of volatiles was considered. The potential sources of attractants are the host larvae, their feces, and the grain infested by the host. Weevil larvae were not attractive. Feces were attractive to females without and females with oviposition experience. Infested grains from which the larvae and feces were removed were slightly attractive to inexperienced, but very attractive to experienced females. Healthy and artificially damaged grains were attractive to experienced parasitoids only. Refering to the “variable response model,” we discuss the effect of experience on the response of the parasitoids to the several stimuli. Stimuli from different trophic levels are used by the foraging parasitoids: feces of the host larvae is an important source of attractants, but also the grains, particularly after experience.     

Inside Pandora's box: Development of the lethal myrmecopathogenic fungus Pandora formicae within its ant host

Parasites modify their host's appearance, behaviour and physiology to a certain extent. Many of these modifications are seen as purposefully manipulative, serving the parasite's interest. Endgames are particularly intriguing, where the parasite's development requires the host's death. ‘Summit’ or ‘treetop’ disease is one of such spectacular examples of parasite-induced death: the host dies attached to an elevated part of the vegetation. Many organisms induce summit disease including Ophiocordyceps, Entomophthora and Pandora species. We analyzed the development of Pandora formicae inside its ant host's body after the host's death. Our findings suggest that the fungus consumes the host's muscles and central nervous system quite fast, similarly to the related Entomophthora muscae. Unlike in Ophiocordyceps, no conidial anastomosis tubes were observed. Differences and similarities between the three fungi are discussed with regard to the extent of parasitic manipulation since Pandora's manipulative traits seem less pronounced than in Ophiocordyceps.