Flight activity in the parasitoid waspNasonia vitripennis (Hymenoptera: Pteromalidae)

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.     

Variation in Propensity to Exhibit Thanatosis in Nasonia vitripennis (Hymenoptera: Pteromalidae)

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.     

Oösorption in Nasonia vitripennis (Hymenoptera: Pteromalidae)

The process of oösorption is described. Leucine amino peptidase and esterase produced by the follicle cells remove the chorion and vitelline membrane. The oölemma grows into the oöcyte and islands of degeneration are formed. The follicle is the entity of oösorption and is isolated from adjoining follicles.
Under conditions of host deprivation oösorption begins earlier in older individuals than younger ones whose fat body is still large before egg production reaches its peak. The time of onset may be correlated with the reduction in the size of the fat body following the peak of egg production. This suggestion is supported by the reduced longevity of starved older individuals compared with younger ones.
Age has no effect on the rate of oösorption.     

Associative Learning in Response to Color in the Parasitoid Wasp Nasonia vitripennis (Hymenoptera: Pteromalidae)

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.     

Associative Learning of Color by Males of the Parasitoid Wasp Nasonia vitripennis (Hymenoptera: Pteromalidae)

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.     

Characterization of phenoloxidase activity in venom from the ectoparasitoid Nasonia vitripennis (Walker) (Hymenoptera: Pteromalidae)

Crude venom isolated from the ectoparasitic wasp Nasonia vitripennis was found to possess phenoloxidase (PO) activity. Enzyme activity was detected by using a modified dot blot analysis approach in which venom samples were applied to nylon membranes and incubated with either L-DOPA or dopamine. Dot formation was most intense with dopamine as the substrate and no activators appeared to be necessary to evoke a melanization reaction. No melanization occurred when venom was incubated in Schneider's insect medium containing 10% fetal bovine serum or when using tyrosine as a substrate, but melanization did occur when larval or pupal plasma from the fly host, Sarcophaga bullata, was exposed to tyrosine. Only fly larval plasma induced an enzyme reaction with the Schneider's insect medium. The PO inhibitor phenylthiourea (PTU) and serine protease inhibitor phenylmethylsulfonylfluoride (PMSF) abolished PO activity in venom and host plasma samples, but glutathione (reduced) only inhibited venom PO. Elicitors of PO activity (sodium dodecyl sulfate and trypsin) had no or a modest effect (increase) on the ability of venom, or larval and pupal plasma to trigger melanization reactions. SDS-PAGE separation of crude venom followed by in-gel staining using L-DOPA as a substrate revealed two venom proteins with PO activity with estimated molecular weights of 68 and 160 kDa. In vitro assays using BTI-TN-5B1-4 cells were performed to determine the importance of venom PO in triggering cellular changes and evoking cell death. When cell monolayers were pre-treated with 10 mM PTU or PMSF prior to venom exposure, the cells were protected from the effects of venom intoxication as evidenced by no observable cellular morphological changes and over 90% cell viability by 24 h after venom treatment. Simultaneous addition of inhibitors with venom or lower concentrations of PMSF were less effective in affording protection. These observations collectively argue that wasp venom PO is unique from that of the fly hosts, and that the venom enzyme is critical in the intoxication pathway leading to cell death.     

The ultrastructure of the mid-gut cells of Nasonia vitripennis (Walker) (Hymenoptera,Pteromalidae)

Summary The ultrastructure of the mid-gut cells of female Nasonia vitripennis is described. The mid-gut consists of a uniform, single-cell epithelium. The cells of different gut regions were analysed using morphometric techniques in order to determine any differences in the components. The structure of the cells is described in the unfed animal, and after varying periods of feeding on host body-fluids. Tissues were sampled after 12 h and 24 h of feeding on host body-fluids and after 24 h feeding/24 h starvation. The cells were found to be complex and contain an organelle component that allows solute-transport and extensive lipid synthesis. A limited cytochemical analysis involving the lysosomal marker enzyme-acid phosphatase — and the respiratory enzyme — cytochrome oxidase was carried out.We are indebted to Professor E.W. Knight-Jones, in whose Department this work was carried out, and to the Science Research Council for financial support to one of us (I.D.)     

Effect of host density on offspring sex ratios and behavioral interactions between females in the parasitoid waspNasonia vitripennis (Hymenoptera: Pteromalidae)

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.     

Formation of protein yolk in the eggs of a parasitoid hymenopteran,Nasonia vitripennis (Walker) (Pteromalidae: Hym)

Summary Electron micrograph profiles of developing yolk inclusions in the oöcytes and comparative electrophoresis of the haemolymph of males and females and of mature oöcytes, indicates that a fraction is present in the haemolymph of the females, which does not occur in the haemolymph of the males. Changes occur to the protein fractions from the haemolymph which are passed into the egg. This suggests that the egg synthesises some of its own yolk and does not have a synthetically passive role during vitellogenesis.We would like to thank Professor E. W. Knight-Jones in whose Department the work was done.     

Functional and nonfunctional female receptivity signals in the parasitoid wasp Spalangia endius (Hymenoptera: Pteromalidae)

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.     

Species-diagnostic single-nucleotide polymorphism and sequence-tagged site markers for the parasitic wasp genus Nasonia (Hymenoptera: Pteromalidae)

Wasps of the genus Nasonia are important biological control agents of house flies and related filth flies, which are major vectors of human pathogens. Species of Nasonia (Hymenoptera: Pteromalidae) are not easily differentiated from one another by morphological characters, and molecular markers for their reliable identification have been missing so far. Here, we report eight single-nucleotide polymorphism and three sequence-tagged site markers derived from expressed sequenced tag libraries for the two closely related and regionally sympatric species N. giraulti and N. vitripennis. We studied variation of these markers in natural populations of the two species, and we mapped them in the Nasonia genome. The markers are species-diagnostic and evenly spread over all five chromosomes. They are ideal for rapid species identification and hybrid recognition, and they can be used to map economically relevant quantitative trait loci in the Nasonia genome.     

Ultrastructural changes in the mitochondria of the acid gland of Nasonia vitripennis (Walker) (Pteromalidae: Hymenoptera) induced by starvation

Summary The formation of mitochondrial-cytoplasmic complexes and their transformation into lipid droplets in the acid gland of Nasonia vitripennis is described. Electron microscopy and histochemistry show that lipid droplets are absent from acid glands in newly emerged, fed and re-fed insects. The droplets develop in the cytoplasm after varying periods of starvation and are not associated with acid phosphatase activity.The mature lipid droplets are rarely associated with intact mitochondria and are probably the residual end-product of the mitochondrial-cytoplasmic associations. The possible role of the associations in the maintenance of mitochondrial function and structure is discussed.We are indebted to Professor E. W. Knight-Jones in whose Department the work was carried out and to the Scientific Research Council for financial assistance to one of us (N.A.R.).     

A fungal-like organism associated with a wasp (Hymenoptera: Pteromalidae) in Dominican amber

A fungal-like organism emerging from a parasitic wasp (Hymenoptera: Pteromalidae) in Dominican amber is characterized. The fossil consists of a white sclerotium-like formation in the wasp's abdomen and a flattened clava-like structure with an ovoid terminus emerging from the sclerotium-like formation. The ovoid terminus bears a protruding elliptical appendix. The fossil, which is characterized by its small size, somatic configuration, pteromalid host and presence in Dominican amber, cannot be placed with assurance in any extant fungal group at this time.     

Sex determination in the haplodiploid wasp Nasonia vitripennis (Hymenoptera: Chalcidoidea): a critical consideration of models and evidence

Sex determining mechanisms are highly diverse. Like all Hymenoptera, the parasitic wasp Nasonia vitripennis reproduces by haplodiploidy: males are haploid and females are diploid. Sex in Nasonia is not determined by complementary alleles at sex loci. Evidence for several alternative models is considered. Recent studies on a polyploid and a gynandromorphic mutant strain point to a maternal product that is balanced against the number of chromosomal complements in the zygote and a parent-specific (imprinting) effect. Research is now focused on the molecular details of sex determination in Nasonia.     

Effects of starvation on the vitellogenesis,ovarian development and fecundity in the ectoparasitoid,Nasonia vitripennis (Hymenoptera: Pteromalidae)

A female‐specific protein, vitellogenin (Vg), and its corresponding egg vitellin (Vt) are identified in the ectoparasitic wasp Nasonia vitripennis. Both native Vt and Vg have a molecular mass of about 350 kDa, which is composed of two subunits of approximately 190 kDa and 165 kDa under reducing and denaturing conditions (sodium dodecyl sulfate—polyacrylamide gel electrophoresis). An indirect sandwich enzyme‐linked immunosorbent assay developed with both monoclonal and polyclonal antibodies against N. vitripennis Vt. Vg was first detected in the hemolymph on the 10th day after parasitism, and was first observed in oocytes on the 12th day. In adults deprived of food, the highest hemolymph Vg level occurred at the time of adult eclosion and the highest level of Vt in ovaries was found at 30 h after eclosion. In contrast, feeding adults with 20% sucrose resulted in the reduction of Vt uptake by ovaries and the extension of life span, but had little effect on Vg production. Deprived of hosts, starvation of female wasps had no significant effects on ovariole growth and oocyte maturation before the wasps died. However, starvation of female wasps supplied with hosts accelerated the wasps laying progeny into hosts, but resulted in a decrease of total progeny production by comparison with wasps fed with 20% sucrose.     

Isolation and characterisation of 26 polymorphic microsatellite markers for the parasitoid wasp Trichogramma dendrolimi (Hymenoptera: Trichogrammatidae)

Polymorphic microsatellite markers were developed for the parasitoid wasp Trichogramma dendrolimi. Forty-four microsatellites were isolated from a (TCG)₈-enriched genomic library and characterised. Twenty-six of these loci were polymorphic and could be used for evaluation of the genetic variation of T. dendrolimi.     

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.     

Differences in egg parasitism of Chrysophtharta agricola (Chapuis) (Coleoptera: Chrysomelidae) by Enoggera nassaui Girault (Hymenoptera: Pteromalidae) in relation to host and parasitoid origin

Abstract The first instances of egg parasitism of Chrysophtharta agricola , a pest of eucalypt plantations, are recorded. Enoggera nassaui was found parasitising C. agricola egg batches in Tasmania, the Australian Capital Territory (ACT), New South Wales and Victoria: this is the first record of this parasitoid species from Victoria. One instance of Neopolycystus sp. parasitising C. agricola eggs in Victoria was also recorded. Parasitism of egg batches by E. nassaui ranged from 0 to 55% between five geographical populations collected in mainland Australia ( n  = 45), and from 0 to 2% between two populations collected in Tasmania ( n  = 300). For mainland sites at which parasitism was recorded, parasitism rates within sites differed significantly from either population in Tasmania. Reciprocal exposure experiments using one Tasmanian (Florentine Valley) and one parasitised mainland (Picadilly Circus, ACT) population were conducted in the laboratory to examine whether these different parasitism rates were attributable to egg or parasitoid origin. Parasitoids from the ACT parasitised C. agricola eggs of both origins more successfully than parasitoids from Tasmania, with up to 65% wasp emergence compared with 33% from Tasmania. Parasitoid origin significantly affected the number of wasps that emerged from exposed batches, but not the total loss from parasitism.