Parasitoid Larval Development Research Articles

The invasive coccinellid Harmonia axyridis (Coleoptera: Coccinellidae) is a less suitable host for parasitism than resident species

Harmonia axyridis (Pallas) has invaded most continents in the world, including South America. In Chile, it became invasive after 2010, turning into a dominant species in coccinellid guilds in alfalfa crops, where it coexists with the introduced species Hippodamia variegata (Goeze) and the native species Eriopis chilensis Hofmann, the populations of which declined after the invasion of H. axyridis. One of the echanisms attributed to the success of invasive species is the enemy release hypothesis (ERH), which predicts that natural enemies will have a lesser impact on the invasive species in the newly invaded areas than on resident species. Dinocampus coccinellae (Hymenoptera: Braconidae) is a cosmopolitan parasitoid of coccinellids, which vary in their suitability to parasitism according to species and location. The present study evaluated whether H. axyridis is a less suitable host than H. variegata and E. chilensis for D. coccinellae by assessing each step in the parasitism process, from oviposition to adult emergence in field and laboratory conditions. In the field, successful parasitism in H. axyridis (7%) was significantly lower than in H. variegata (33%) and E. chilensis (36%). H. axyridis was also the only species in which failed parasitoid larval development was greater than successful parasitism (adult emergence). In the laboratory, D. coccinellae never successfully oviposited in H. axyridis, while it did in the other two species. These results suggest that in Chile, H. axyridis is a less suitable host than the resident species for D. coccinellae. This mechanism, among others, may explain the dominance of this species in this early stage of invasion

In vivo and in vitro developmental profiling of Asobara japonica, a larval endoparasitoid of drosophilid flies

AbstractThe relationship between host and parasitoid has been examined in terms of either the effects of infestation on host growth and development, or the growth and development of parasitoid larvae in response to the physiological and nutritional status of their hosts. Although a wide range of host–parasitoid interactions has been studied, detailed developmental profiles of parasitoid larvae and environmental effects on them have remained unclear in many cases because the parasitoid larvae are relatively inaccessible inside their hosts. Here, we used Drosophila melanogaster Meigen (Diptera: Drosophilidae) and Asobara japonica Belokobylskij (Hymenoptera: Braconidae) as a model system to describe developmental profiles of hosts and endoparasitoid wasps, and investigated environmental factors that affect the developmental profiles in in vivo and in vitro culture experiments. As a result, we successfully identified six morphologically distinct developmental stages (I–VI) of pre‐adult A. japonica. The current approach based on qualitative and quantitative assessment of wasp morphology may be an effective approach for estimating the instar number of endoparasitoids lacking sclerotized structures in general. The finding that the development of A. japonica from stage III to stage IV is constrained by host developmental stage regardless of the environmental conditions in this study suggests that developmental mismatch may be an important factor in the evolution of host selection in endoparasitoid wasps.

Effects of Three Insect Growth Regulators on Encarsia formosa (Hymenoptera: Aphelinidae), an Endoparasitoid of Bemisia tabaci (Hemiptera: Aleyrodidae).

Insect growth regulators (IGRs) disrupt the normal activity of the endocrine or hormone system of insects, affecting the development, reproduction, or metamorphosis of the target insects, and normally causing less detrimental effects to beneficial insects. The effects of three IGRs (pyriproxyfen, fenoxycarb, and buprofezin) on Encarsia formosa Gahan, an endoparasitoid of whiteflies, were determined using B. tabaci as a host. We assessed the effects of the IGRs on parasitoid's larval development, pupation, emergence, and contact effects of the dry residues on plant leaf and glass vial surface on adult mortality and parasitism. When the three IGRs were applied at larval stage, no or few larvae pupated in the pyriproxyfen treatments and the highest concentration of fenoxycarb, and a majority of larvae pupated in the buprofezin treatments; of those pupated, 62.3-88.1% became adults. When the IGRs were applied at the pupal stage, 2.3-17.5% developed to adults in the pyriproxyfen treatments, 59.7-89.0% in the fenoxycarb treatments, and 58.4-83.6% in the buprofezin treatments. The leaf residues of the IGRs had no appreciable effects on adults, whereas the residues on glass vial caused significantly lower adult survival than on plant leaves. The residues of pyriproxyfen and fenoxycarb slightly reduced parasitism as compared with buprofezin and controls. However, the rates of parasitoids that became adults were significantly lower, especially in the pyriproxyfen treatments. According to the standards of International Organization of Biological Control (IOBC), pyriproxyfen was harmful, while fenoxycarb and buprofezin were slightly or moderately harmful to larvae and harmless to E. formosa pupae.

Host behavioural manipulation of two orb-weaver spiders by parasitoid wasps

Parasitic infection or tissue consumption by parasitoids typically leads to several phenotypic alterations in hosts, including distinct changes in behavioural, morphological, or life history traits. Some of these changes may not result solely from host responses, but actively induced changes by parasites/parasitoids to manipulate the host to acquire some benefit (e.g. parasite/parasitoid survivorship or dispersal ability). Field experiments investigating the effects of host behavioural alterations on parasite or parasitoid survivorship and the mechanisms involved in these changes are important for confirmation of behavioural manipulation. In the present study, we examined web design modification in the host spider species Cyclosa fililineata and Cyclosa morretes, which are attacked by the polysphinctine ectoparasitoid wasps Polysphincta sp. nr. purcelli and Polysphincta janzeni, respectively. We tested whether changes in orb spider web design (1) result from nutritional restrictions imposed by parasitoids and (2) increase the chances of adult wasp emergence from the cocoon. Furthermore, we describe changes in web design consistent with parasitoid larval development. Results, for both spider species, showed that web design modifications occurred only during the night preceding host spider death, and that modifications involved a reduction in the number of spirals and radii of orb webs. Food restriction did not generate web design modification, suggesting that observed changes in host behaviour resulted from direct actions of parasitoid larvae rather than as a by-product of nutritional deficiencies. Rain events were the major factor causing web rupture and subsequent parasitoid mortality. Modifications in web design reduced the frequency of web ruptures, increasing parasitoid adult emergence, and thus survivorship probability, during the pupal stage. These results confirm that web modifications by spiders are adaptive to parasitoid wasps.

Assessing the Total Mortality Caused by Two Species of Trichogramma on Its Natural Host Plutella xylostella (L.) at Different Temperatures.

Trichogramma pretiosum Riley and Trichogramma atopovirilia Oatman & Platner are natural enemies of Plutella xylostella (L.) in Southern Brazil. Laboratory studies to evaluate parasitoids performance under different conditions, such as temperature regimes, are necessary to assess their potential as biocontrol agents of P. xylostella. In most studies involving Trichogramma, parasitism rate is the main parameter used to evaluate parasitoid performance, ignoring that parasitoids can cause egg mortality by feeding on the host content and/or to multiple drilling without laying eggs. This study was conducted to investigate three main issues: how temperature affects T. pretiosum and T.atopovirilia development on eggs of P. xylostella, whether or not these species respond differently to temperature, and how important is the mortality they cause besides parasitism on P. xylostella. Temperature effects (from 10 to 30°C) on development, survival, parasitism rate, mortality, and total mortality caused by T. pretiosum and T. atopovirilia on eggs of P. xylostella were evaluated. Temperature affected the development time, female longevity, parasitism rate, mortality not directly related to parasitoid larval development, and total mortality caused on the host. No significant differences were recorded for the estimated thermal requirements for T. pretiosum and T. atopovirilia. However, the higher mortality caused by T. pretiosum indicates that this parasitoid is the most suitable to be used against P. xylostella. Also, the results suggest that the use of parasitism rate as the only parameter to evaluate the performance of T. pretiosum and T. atopovirilia may underestimate the potential of these parasitoids in regulating pest populations.

Four heat shock protein genes of the endoparasitoid wasp, Cotesia vestalis, and their transcriptional profiles in relation to developmental stages and temperature.

Heat shock proteins (Hsps) play important roles in the environmental adaptation of various organisms. To explore the functions of Hsps in relation to heat stress and development in Cotesia vestalis, a solitary larval endoparasitoid of Plutella xylostella, four heat shock protein genes, CvHsp40, CvHsc70, CvHsp70 and CvHsp90, were cloned and sequenced from C. vestalis by real-time quantitative PCR and RACE. The cDNA sequence of CvHsp40, CvHsc70, CvHsp70 and CvHsp90 were 1473 bp, 2316 bp, 2279 bp and 2663 bp long, which encode proteins with calculated molecular weights (MW) of 39.1 kDa, 71.2 kDa, 70.1 kDa and 83.3 kDa, respectively. Furthermore, the analysis of genomic DNA confirmed that no introns existed in CvHsp40, CvHsp70 and CvHsp90 while two introns were present in CvHsc70. The amino acid sequence analysis of CvHsps indicated that CvHsp40 is a Type II Hsp40 homolog, CvHsp70 and CvHsc70 are the eukaryotic cytoplasmic Hsp70s, and CvHsp90 is the β-isoform of Hsp90. The divergent transcriptional patterns of CvHsp40, CvHsp70 and CvHsp90 in the different developmental stages suggested that CvHsp transcripts were under different mechanisms of regulation during the development of parasitoid larvae. The dramatic increase of transcripts of CvHsp70 at the third-instar larva coincided with its developmental change in this stage, that is, from inside host to outside host. CvHsp40, CvHsc70 and CvHsp70 showed a trend of sex-specific differences of transcript abundance in the adult stage. All CvHsp transcripts in different developmental stages were significantly induced by heat stress, and the lowest transcript abundances appeared around the temperature 27°C, which probably suggest that this is the most favorable temperature for the development of C. vestalis. Our results suggest that the expression of heat shock proteins reflects to some extent the developmental changes and environmental requirements of insects.

Effect of Binodoxys communis parasitism on flight behavior of the soybean aphid, Aphis glycines

Many aphid species possess wingless (apterous) and winged (alate) stages, both of which can harbor parasitoids at various developmental stages. Winged aphids bearing parasitoid eggs or young larvae can potentially still engage in long-distance flights and thereby facilitate parasitoid dispersal, which has important implications for biological control of aphids by parasitoids. In this study, we determined the effect of parasitism by Binodoxys communis (Hymenoptera: Braconidae) on wing development and flight of the summer alate stage of the soybean aphid, Aphis glycines (Hemiptera: Aphididae), and quantified the effect of aphid flight duration on subsequent B. communis development. Parasitism by B. communis was allowed at alatoid 3rd (L3) and 4th instar (L4) nymphal stages of A. glycines and subsequent aphid flight was measured using a computer-monitored flight mill. Only 25% of aphids parasitized as L3 alatoid nymphs produced normal winged adults, compared to 100% of L4 alatoids. While flight performance of aphids that had been parasitized as 4th-instar alatoid nymphs 24 or 48h prior to testing was similar to that of unparasitized alates of identical age, it declined sharply for alates that had been parasitized as 4th-instar alatoid nymphs 72 and 96h prior to testing. Parasitoid larval and pupal development times, percent mummification and adult emergence rates did not differ between treatments in which aphids had flown over varying durations. Our results have implications for natural biological control of A. glycines in Asia and classical biological control of the soybean aphid in North America.

Consequences of constitutive and induced variation in the host’s food plant quality for parasitoid larval development

Constitutive and induced changes in plant quality impact higher trophic levels, such as the development of parasitoids, in different ways. An efficient way to study how plant quality affects parasitoids is to examine how the parasitoid larva is integrated within the host during the growth process. In two experiments, we investigated the effects of varying nutritional quality of Brassica oleracea on parasitoid larval development inside the host, the diamondback moth (Plutella xylostella). First, we compared larval growth of the specialist Diadegma semiclausum and the generalist Diadegma fenestrale, when the host was feeding on Brussels sprout plants that were either undamaged or were previously induced by caterpillar damage. Larvae of the generalist D. fenestrale showed lower growth rates than larvae of the specialist D. semiclausum, and this difference was more pronounced on herbivore-induced plants, suggesting differences in host-use efficiency between parasitoid species. The growth of D. semiclausum larvae was also analyzed in relation to herbivore induction on Brussels sprouts and on a wild B. oleracea strain. Parasitoid growth was more depressed on induced than on undamaged control plants, and more on wild cabbage than on Brussels sprouts, which was largely explained by differences in host mass. The effects of induction of wild Brassica on parasitoid development were pronounced early on, but as P. xylostella feeding began inducing the previously undamaged control plants, the effect of induction disappeared, revealing a temporal component of plant–parasitoid interactions. This study demonstrates how insights into the physiological aspects of host–parasitoid interactions can improve our understanding of the effects of plant-related traits on parasitoid wasps.

Plant-mediated effects of different Salix species on the performance of the braconid parasitoid Perilitus brevicollis

The blue willow beetle, Phratora vulgatissima, is considered to be the most damaging herbivorous pest in Salix short-rotation coppices throughout Europe. The braconid parasitoid Perilitus brevicollis is an important natural enemy of Phratora. As several different Salix species are used in coppices, I investigated the bottom–up (tritrophic) effects of Salix on the parasitoid. Three host plants were studied: the introduced fast-growing S. viminalis, which is highly susceptible to the beetle; S. dasyclados, which is introduced and moderately-resistant to the beetle; and the native slow-growing Salix cinerea, which is not currently used in coppices. The identity of the host-plant species had significant effects on parasitoid larval development time; parasitoids developed rapidly on the susceptible S. viminalis and slowly on the moderately resistant S. dasyclados. Increased development time resulted in reduced adult longevity. Host-plant species identity also affected larval survival; 57%, 64%, and 49% of the parasitoids successfully completed larval development in beetles fed S. viminalis, S. cinerea, and S. dasyclados, respectively. Parasitoid development was also correlated with the body size of their beetle host, but this effect was independent of the identity of the host-plant species. The results of this study suggest that the parasitoid has higher survival and growth rates when it parasitizes beetles feeding on the common coppice species S. viminalis, but the performance of the parasite is reduced when the beetle feeds on the moderately-resistant S. dasyclados. Conversely, the omnivorous biocontrol agents sometimes used in these systems appear to perform better on S. dasyclados compared to S. viminalis. The results of this study suggest that Perilitus parasitoids and omnivorous beetle predators may provide complementary protection to Salix and therefore be useful in coppice management.

Biology and development of Chaetophthalmus dorsalis (Malloch) (Diptera: Tachinidae) parasitising Helicoverpa armigera (Hübner) and H. punctigera Wallengren (Lepidoptera: Noctuidae) larvae in the laboratory

Chaetophthalmus dorsalis is a common larval parasitoid of several economically important species of Noctuidae in Australia but little is known about its biology. This paper describes aspects of the behaviour and development of C. dorsalis parasitising Helicoverpa armigera and H. punctigera larvae in the laboratory. At 25°C, C. dorsalis laid a mean of 577 ovolarviparous eggs, 8–9 days after emergence. Parasitoids were able to complete development when newly emerged planidia were placed on all host instars except first instars. Planidia manually placed on the dorsum of the first thoracic segment of host larvae showed no preference to penetrate segments immediately behind the head capsule where they could not be removed by the host. Planidia were significantly faster at penetrating the cuticle of early- (second to fourth) instar compared with late- (fifth and sixth) instar larvae, and late-instar H. punctigera larvae compared with equivalent instars of H. armigera. Parasitoid larval development was significantly faster when planidia were placed on late-instar H. punctigera larvae than on early-instar larvae but puparium development and puparium weight were not affected by host age. Parasitised Helicoverpa larvae gained weight at the same rate as unparasitised larvae until 2–3 days before the exit of C. dorsalis larvae when they entered a premature prepupal phase. Developmental thresholds and day-degree requirements for C. dorsalis were calculated and compared with H. armigera. A new host record for C. dorsalis reared from Neocleptria punctifera (Noctuidae) larvae is given.

Effect of parasitism on flight behavior of the soybean aphid, Aphis glycines

Many aphid species possess wingless (apterous) and winged (alate) stages, both of which can harbor parasitoids at various developmental stages. Alates can either be parasitized directly or can bear parasitoids eggs or larvae resulting from prior parasitism of alatoid nymphs. Winged aphids bearing parasitoid eggs or young larvae eventually still engage in long-distance flights, thereby facilitating parasitoid dispersal. This may have a number of important implications for biological control of aphids by parasitoids. In this study, we determined the effect of parasitism by Aphelinus varipes (Hymenoptera: Aphelinidae) on wing development and flight of the soybean aphid, Aphis glycines (Hemiptera: Aphididae). We also quantified the influence of aphid flight distance on subsequent A. varipes development. Parasitism by A. varipes was allowed at different A. glycines developmental stages (i.e., alatoid 3rd and 4th-instar nymphs, alates) and subsequent aphid flight was measured using a computer-monitored flight mill. Only 35% of aphids parasitized as L3 alatoid nymphs produced normal winged adults compared to 100% of L4 alatoids. Flight performance of aphids parasitized as 4th-instar alatoid nymphs 24 or 48h prior to testing was similar to that of un-parasitized alates of identical age, but declined sharply for alates that had been parasitized as 4th-instar alatoid nymphs 72 and 96h prior to testing. Flight performance of aphids parasitized as alate adults for 24h was not significantly different from un-parasitized alates of comparable ages. Flight distance did not affect parasitoid larval or pupal development times, or the percent mummification of parasitized aphids. Our results have implications for natural biological control of A. glycines in Asia and classical biological control of the soybean aphid in North America.

Changes in the hemolymph and fat body metabolites of Diatraea saccharalis (Fabricius) (Lepidoptera: Crambidae) parasitized by Cotesia flavipes (Cameron) (Hymenoptera: Braconidae)

The koinobiont Cotesia flavipes responds to and is influenced by biochemical changes in the host hemolymph composition, Diatraea saccharalis. Changes in the composition of macronutrients may occur due to the hosts own development or by changes induced after parasitization. These changes occur to facilitate parasitoid invasion and to make the host internal environment suitable to parasitoid immature development. Therefore, changes in the availability of stored and circulating nutrients may correlate with the nutritional requirements of specific parasitoid immature stages. In here, we describe changes in the biochemical composition of parasitized and control larvae at different stages of parasitoid development to gain information on C. flavipes host regulation and on its quantitative immature nutritional requirements. Total proteins, lipids and carbohydrates free in the hemolymph or stored in host fat bodies, and the SDS–PAGE protein profile of the hemolymph were evaluated in control and parasitized 6th instar during the whole parasitoid development. Changes in the total protein available in the host hemolymph were detected soon after parasitization, but carbohydrate and lipids were observed to differ only towards parasitoid larvae egression. Although C. flavipes affected the availability of all macronutrients observed in the host hemolymph, lipids and proteins stored in the host fat bodies were unaffected. However, carbohydrate concentration at the end of parasitoid larval development was much lower in parasitized than in control larvae at the same stage of development. SDS–PAGE analysis indicated C. flavipes up-regulated two host proteins (125 and 48kDa) and released two parasitism-specific proteins towards the end of parasitoid larval development. We provide a discussion on the role these changes may have on the process of host regulation and their possible requirement to sustain parasitoid development.

Effects of Bacillus thuringiensisδ‐endotoxin‐fed Helicoverpa armigera on the survival and development of the parasitoid Campoletis chlorideae

AbstractWith the deployment of transgenic crops expressing δ‐endotoxins from Bacillus thuringiensis (Bt) for pest management, there is a need to generate information on the interaction of crop pests with their natural enemies that are important for regulation of pest populations. Therefore, we studied the effects of the Bt δ‐endotoxins Cry1Ab and Cry1Ac on the survival and development of the parasitoid Campoletis chlorideae Uchida (Hymenoptera: Ichneumonidae) reared on Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) larvae fed on Bt toxin‐intoxicated artificial diet. The H. armigera larvae fed on artificial diet impregnated with Cry1Ab and Cry1Ac at LC50 (effective concentration to kill 50% of the neonate H. armigera larvae) and ED50 (effective concentration to cause a 50% reduction in larval weight) levels before and after parasitization resulted in a significant reduction in cocoon formation and adult emergence of C. chlorideae. Larval period of the parasitoid was prolonged by 2 days when fed on Bt‐intoxicated larvae. No adverse effects were observed on female fecundity. The observed effects appeared to be indirect in nature, because no Bt proteins were detected through enzyme‐linked immunosorbent assay in the C. chlorideae larvae, cocoons, or adults fed on Cry1Ab‐ or Cry1Ac‐treated H. armigera larvae. The effects of Bt toxin proteins on C. chlorideae were due to early mortality of H. armigera larvae, that is, before completion of parasitoid larval development.

Host discrimination by the endoparasitoid Psyllaephagus pistaciae (Hymenoptera: Encyrtidae): A case of time-dependent ability

Host-discrimination behavior by the koinobiont parasitoid, Psyllaephagus pistaciae Ferrière (Hymenoptera: Encyrtidae), the major biocontrol agent of the common pistachio psylla, Agonoscena pistaciae Burckhardt & Lauterer (Hemiptera: Psyllidae), in Iran, was investigated in the laboratory. The results demonstrated that P. pistaciae quickly detected and avoided freshly parasitized hosts, either after antennating or by probing with their ovipositor. However, this discriminatory ability declined with time, probably influenced by both external and internal markers left by the previous ovipositing female. The results also confirmed that female P. pistaciae responded to changes in host quality associated with the parasitoid's larval development 4 days after the initial parasitization, clearly indicating that the second female could detect the presence of the larvae and adjust her host-selection decision. In addition, psyllid nymphs treated topically with a solution of Dufour's gland were rejected by the parasitoid, showing that Dufour's gland secretion had a significant effect as a host marking chemical. The current study also showed that superparasitism increased the host-mortality and that the rate of encapsulation decreased, suggesting that, when two eggs are laid in the same psyllid nymph, only one parasitoid develops to an adult.

Zombie fire ant workers: behavior controlled by decapitating fly parasitoids

Laboratory observations were conducted on four separate red imported fire ant, Solenopsis invicta, colonies that contained workers parasitized by the decapitating fly, Pseudacteon tricuspis. Parasitized S. invicta workers remained inside the nest during parasitoid larval development and left the nest approximately 8 – 10 hours before decapitation by the parasitoid. When parasitized ants left the nest, they were highly mobile, were responsive to tactile stimuli, and showed minimal defensive behavior. Ants ultimately entered into a grass thatch layer, where they were decapitated and the fly maggots pupariated. This study reveals that parasitized ants exhibit behaviors that are consistent with host manipulation to benefit survival of the parasitoid.

Teratocytes growth pattern reflects host suitability in a host–parasitoid assemblage

Abstract In some parasitoid species, the serosa membrane breaks apart at hatching and produces teratocyte cells that assume various functions (immunossupression, secretion and nutrition) mediating host–parasitoid relationships. Teratocyte growth pattern may thus reflect the host suitability for a parasitoid. The teratocyte growth pattern (increase in size and number of teratocytes as a function of time) is studied and used as an indirect measure of fitness to compare the development of the endoparasitoid Dinocampus coccinellae in a marginal host, the coccinellid Harmonia axyridis, and in a suitable host, Coleomegilla maculata. Indirect measures of fitness recorded in both host species confirm that C. maculata is a suitable host for D. coccinellae contrary to the marginal host H. axyridis. According to regression analysis, teratocyte numbers decrease linearly whereas teratocyte size increases linearly with time in the suitable host C. maculata (larvae or adults). In the marginal host, parasitism occurs only in the larval stage where a delay in the parasitoid larval development is observed. Increase in teratocyte size is also highly variable. The teratocyte growth pattern of the parasitoid in the marginal host does not follow the linear model found in the suitable host. Teratocyte growth pattern may be a useful criterion to evaluate host‐suitability and host range of parasitoids.

Host regulation and release of parasitism-specific proteins in the system Toxoneuron nigriceps– Heliothis virescens

The braconid wasp Toxoneuron nigriceps induced qualitative and quantitative changes in the protein composition of the moth Heliothis virescens host hemolymph. Total protein concentration was found to be higher in parasitized host 4 days after parasitism as compared to control hosts, mainly due to changes in a particular group of proteins. Host proteins with a molecular mass of 173 and 72 kDa were found in higher levels in the hemolymph of parasitized larvae as control hosts approached pupation, while an 80 kDa peptide was found in reduced concentration in the hemolymph of parasitized hosts. Levels of these three peptides were maintained throughout parasitoid development, while two of them (173 and 72 kDa) were cleared from the host hemolymph close to pupation. Besides the regulation of host proteins, three parasitism-specific proteins (PSPs) were released into the host hemolymph. Two of them (PSP1-MW = 116 kDa, p I = 6.3; PSP2-MW = 114 kDa, p I = 6.2) first appeared in the hemolymph of parasitized hosts soon after pupation of control host and increased in concentration as the parasitoid developed. The third PSP (PSP3-MW = 56 kDa, p I = 5.8) was produced towards the end of parasitoid larval development, close to parasitoid egression. Database searches based on the amino acid composition and amino terminal sequence of PSP1 and PSP2 did not produce any significant matches, while PSP3 was identified as a putative chitinase. Incubation of host derived tissues, parasitoid larvae and teratocytes in 35S conditioned media suggested PSPs were a product of teratocytes. The role of the regulation of host proteins and release of PSPs by teratocytes for the successful development of T. nigriceps are discussed.

Interactions between the solitary endoparasitoid, Meteorus gyrator (Hymenoptera: Braconidae) and its host, Lacanobia oleracea (Lepidoptera: Noctuidae), infected with the entomopathogenic microsporidium, Vairimorpha necatrix (Microspora: Microsporidia)

Infection of Lacanobia oleracea (Linnaeus) larvae with the microsporidium Vairimorpha necatrix (Kramer) resulted in significant effects on the survival and development of the braconid parasitoid, Meteorus gyrator (Thunberg). Female M. gyrator did not show any avoidance of V. necatrix-infected hosts when they were selecting hosts for oviposition. When parasitism occurred at the same time as infection by the pathogen, or up to four days later, no significant detrimental effects on the parasitoid were observed. However, when parasitism occurred six to eight days after infection, a greater proportion (12.5-14%) of hosts died before parasitoid larvae egressed. Successful eclosion of adult wasps was also reduced. When parasitism and infection were concurrent, parasitoid larval development was significantly faster in infected hosts, and cocoons were significantly heavier. However, as the time interval between infection and parasitism increased, parasitoid larval development was significantly extended by up to two days, and the cocoons formed were significantly (c. 20%) smaller. Vairimorpha necatrix spores were ingested by the developing parasitoid larvae, accumulated in the occluded midgut, and were excreted in the meconium upon pupation.

Genome sequence of a polydnavirus: insights into symbiotic virus evolution.

Little is known of the fate of viruses involved in long-term obligatory associations with eukaryotes. For example, many species of parasitoid wasps have symbiotic viruses to manipulate host defenses and to allow development of parasitoid larvae. The complete nucleotide sequence of the DNA enclosed in the virus particles injected by a parasitoid wasp revealed a complex organization, resembling a eukaryote genomic region more than a viral genome. Although endocellular symbiont genomes have undergone a dramatic loss of genes, the evolution of symbiotic viruses appears to be characterized by extensive duplication of virulence genes coding for truncated versions of cellular proteins.

Unexpected Listronotus bonariensis (Coleoptera: Curculionidae) mortality in the presence of parasitoids.

Field enclosure and laboratory cage experiments designed to measure the impact of the parasitoid Microctonus hyperodae Loan on the Argentine stem weevil, Listronotus bonariensis (Kuschel) have shown that under high parasitoid pressure, there is significant weevil mortality without obvious parasitism. Parasitoid-exposed, but unparasitized portions of caged populations died at rates significantly higher than both the parasitized weevils from the same population and the unexposed controls. Unexpectedly, parasitized weevils had the lowest mortality rates (prior to larval parasitoid emergence). It was of ecological significance that this mortality effect was detected under field conditions using several years of empirically-collected population dynamics data. Under both field and laboratory conditions this mortality was found to occur within shorter time intervals than that required for full parasitoid larval development; thus it could not be attributed to the mortality that occurs after the emergence of prepupal parasitoids. The mechanism for this mortality remains undetermined, although it could possibly be linked to pseudoparasitism.