Parasitization of Manduca sexta larvae by the parasitoid wasp Cotesia congregata induces an impaired host immune response

During oviposition, the parasitoid wasp Cotesia congregata injects polydnavirus, venom, and parasitoid eggs into larvae of its lepidopteran host, the tobacco hornworm, Manduca sexta. Polydnaviruses (PDVs) suppress the immune system of the host and allow the juvenile parasitoids to develop without being encapsulated by host hemocytes mobilized by the immune system. Previous work identified a gene in the Cotesia rubecula PDV (CrV1) that is responsible for depolymerization of actin in hemocytes of the host Pieris rapae during a narrow temporal window from 4 to 8h post-parasitization. Its expression appears temporally correlated with hemocyte dysfunction. After this time, the hemocytes recover, and encapsulation is then inhibited by other mechanism(s). In contrast, in parasitized tobacco hornworm larvae this type of inactivation in hemocytes of parasitized M. sexta larvae leads to irreversible cellular disruption. We have characterized the temporal pattern of expression of the CrV1-homolog from the C. congregata PDV in host fat body and hemocytes using Northern blots, and localized the protein in host hemocytes with polyclonal antibodies to CrV1 protein produced in P. rapae in response to expression of the CrV1 protein. Host hemocytes stained with FITC-labeled phalloidin, which binds to filamentous actin, were used to observe hemocyte disruption in parasitized and virus-injected hosts and a comparison was made to hemocytes of nonparasitized control larvae. At 24h post-parasitization host hemocytes were significantly altered compared to those of nonparasitized larvae. Hemocytes from newly parasitized hosts displayed blebbing, inhibition of spreading and adhesion, and overall cell disruption. A CrV1-homolog gene product was localized in host hemocytes using polyclonal CrV1 antibodies, suggesting that CrV1-like gene products of C. congregata's bracovirus are responsible for the impaired immune response of the host.     

Host refractoriness of the tobacco hornworm, Manduca sexta, to the braconid endoparasitoid Cotesia flavipes

Cotesia flavipes (Hymenoptera:Braconidae) is a gregarious endoparasitoid of several pyralid stemborer larvae of economic significance including the sugarcane borer, Diatraea saccharalis. In this study, the ability of this parasitoid to develop in a sphingid host, Manduca sexta, was tested. First, second, third, fourth, and even pharate fifth instar host tobacco hornworm larvae were readily parasitized by the female C. flavipes parasitoids but no wasp larvae hatched from the eggs in this refractory host. Instead, the parasitoid eggs were invariably encapsulated by the host's hemocytes and, ultimately, no parasitoids emerged from tobacco hornworm hosts. The first stages of encapsulation were evident at 2 h post-parasitization of the host M. sexta larvae, when the beginning stages of capsule formation were seen. The developmental fate of the host larvae with encapsulated parasitoids was variable. Most succumbed as abnormally small fifth instars or as post-wandering prepupal animals, while a few developed normally to the pupal stage. Dissection of all the larvae or pupae with encapsulated wasp eggs showed evidence of hemocytic encapsulation and melanization of the C. flavipes eggs. This report describes the association between C. flavipes and M. sexta, which appears to be an excellent model system for studying the physiological processes accompanying wasp egg encapsulation that result in death of the host as well as the parasitoid. Since the parasitoid egg never hatches, the system offers an excellent opportunity to identify and study the effects of parasitoid-injected polydnavirus and venom on host physiology.     

两种金小蜂毒液对菜粉蝶蛹血细胞延展、存活及包囊作用的影响

活体微注射测定结果表明,将0.5毒囊当量（venom reservoir equivalent, VRE）的蝶蛹金小蜂毒液注射于其寄主菜粉蝶蛹体内,注射后4～24 h寄主浆血细胞和颗粒血细胞的延展、存活和对Sephadex A50微珠的包囊能力显著下降;以0.002～0.02 VRE/μL的该蜂毒液处理其离体寄主血细胞均能产生同样的生理效应。该毒液抑制90%菜粉蝶蛹浆血细胞和颗粒血细胞延展的浓度各为0.00076 VRE/μL和0.00804 VRE/μL。可见,蝶蛹金小蜂毒液能显著抑制其寄主血细胞的延展和包囊作用,并导致血细胞的死亡。然而,同样条件下丽蝇蛹集金小蜂毒液对其非自然寄主菜粉蝶蛹的血细胞延展、存活和包囊作用则无任何效应。可见,寄生蜂毒液的生理作用具有明显的寄主特异性。     

Effects of host (Boettcherisca peregrina) copper exposure on development, reproduction and vitellogenesis of the ectoparasitic wasp, Nasonia vitripennis

Effects of copper (Cu) accumulation by the flesh fly Boettcherisca peregrina (R.-D.) (Diptera: Sarcophagidae) on the ectoparasitic wasp Nasonia vitripennis (Walker) (Hymenoptera: Pteromalidae) were investigated experimentally by exposing host larvae to contaminated diets with final Cu concentrations of 400 μg/g and 800 μg/g diet fresh weight (DFW), respectively. Results showed that Cu can be transferred along food chains to secondary consumers (parasitoids) in small amounts, resulting in negative effects on parasitoid growth and development (body weight and developmental duration) as well as fecundity (number of offspring per female). Copper exposure also inhibited vitellogenesis of parasitoids from Cu-contaminated host pupae. It is suggested that the decreased fecundity and inhibition of vitellogenesis of N. vitripennis resulted from poor host nutritional state rather than from direct effects of Cu stress.     

Immunity of an alternative host can be overcome by higher densities of its parasitoids Palmistichus elaeisis and Trichospilus diatraeae

Interactions of the parasitoids Palmistichus elaeisis Delvare & LaSalle and Trichospilus diatraeae Cherian & Margabandhu (Hymenoptera: Eulophidae) with its alternative host Anticarsia gemmatalis (Hübner) (Lepidoptera: Noctuidae) affect the success or failure of the mass production of these parasitoids for use in integrated pest management programs. The aim of this study was to evaluate changes in the cellular defense and encapsulation ability of A. gemmatalis pupae against P. elaeisis or T. diatraeae in adult parasitoid densities of 1, 3, 5, 7, 9, 11 or 13 parasitoids/pupae. We evaluated the total quantity of circulating hemocytes and the encapsulation rate versus density. Increasing parasitoid density reduced the total number of hemocytes in the hemolymph and the encapsulation rate by parasitized pupae. Furthermore, densities of P. elaeisis above 5 parasitoids/pupae caused higher reduction in total hemocyte numbers. The encapsulation rate fell with increasing parasitoid density. However, parasitic invasion by both species induced generally similar responses. The reduction in defensive capacity of A. gemmatalis is related to the adjustment of the density of these parasitoids to their development in this host. Thus, the role of the density of P. elaeisis or T. diatraeae by pupa is induced suppression of cellular defense and encapsulation of the host, even without them possesses a co-evolutionary history. Furthermore, these findings can predict the success of P. elaeisis and T. diatraeae in the control of insect pests through the use of immunology as a tool for evaluation of natural enemies.     

Does the solitary parasitoid Microplitis pennatulae use a combinatorial approach to manipulate its host?

Host manipulation is a strategy used by some parasites to enhance their transmission. These parasites use a combination of neuropharmacological, psychoneuroimmunological, genomic/proteomic, or symbiont-mediated mechanisms to manipulate their hosts. Bodyguard manipulation occurs when parasitized hosts guard parasitoid pupae to protect them from their natural enemies. Bodyguard-manipulated hosts exhibit altered behaviours only after the egression of parasitoid prepupae. Behavioural changes in post-parasitoid egressed hosts could have resulted from their altered physiology. Previous studies have shown that gregarious manipulative parasitoids induce multiple physiological changes in their host, but the physiological changes induced by solitary manipulative parasitoids are unknown. Microplitis pennatulae Ranjith & Rajesh (Hymenoptera: Braconidae) is a larval parasitoid of Psalis pennatula Fabricius (Lepidoptera: Erebidae). After the egression of parasitoid prepupae, P. pennatula stops its routine activities and protects the parasitoid pupa from hyperparasitoids by body thrashes. In this study, we looked into the physiological changes induced by the solitary manipulative parasitoid, M. pennatulae, in its host, P. pennatula, during various stages of parasitization. We considered octopamine concentration and phenoloxidase (PO) activity as biomarkers of physiological change. We also examined whether M. pennatulae has a symbiotic virus and whether the wasp transfers it to the host during parasitization. We found that octopamine concentration was low in the pre-parasitoid egressed host, but it was elevated after the parasitoid egressed. Phenoloxidase activity was lower in the pre- and post-parasitoid egressed host than in the unparasitized host. We also detected symbiotic bracovirus (BV) in the wasp ovaries and isolated the BV virulence gene from the parasitised host. Our study suggests that solitary parasitoids also induce multiple physiological changes to influence the host behaviour to their advantage, as is the case with the gregarious parasitoids.     

Parasitism and venom of ectoparasitoid Scleroderma guani impairs host cellular immunity

Venom is a prominently maternal virulent factor utilized by parasitoids to overcome hosts immune defense. With respect to roles of this toxic mixture involved in manipulating hosts immunity, great interest has been mostly restricted to Ichneumonoidea parasitoids associated with polydnavirus (PDV), of which venom is usually considered as a helper component to enhance the role of PDV, and limited Chalcidoidea species. In contrast, little information is available in other parasitoids, especially ectoparasitic species not carrying PDV. The ectoparasitoid Scleroderma guani injects venom into its host, Tenebrio molitor, implying its venom was involved in suppression of hosts immune response for successful parasitism. Thus, we investigated the effects of parasitism and venom of this parasitoid on counteracting the cellular immunity of its host by examining changes of hemocyte counts, and hemocyte spreading and encapsulation ability. Total hemocyte counts were elevated in parasitized and venom‐injected pupae. The spreading behavior of both granulocytes and plasmatocytes was impaired by parasitization and venom. High concentration of venom led to more severely increased hemocyte counts and suppression of hemocyte spreading. The ability of hemocyte encapsulation was inhibited by venom in vitro. In addition to immediate effects observed, venom showed persistent interference in hosts cellular immunity. These results indicate that venom alone from S. guani plays a pivotal role in blocking hosts cellular immune response, serving as a regulator that guarantees the successful development of its progenies. The findings provide a foundation for further investigation of the underlying mechanisms in immune inhibitory action of S. guani venom.     

Cytotoxic effects of parasitism and application of venom from the endoparasitoid Pimpla turionellae on hemocytes of the host Galleria mellonella

In parasitoid species devoid of polydnaviruses and virus‐like particles, venom appears to play a major role in suppression of host immunity. Venom from the pupal endoparasitoid Pimpla turionellae L. (Hymenoptera: Ichneumonidae) has previously been shown to contain a mixture of biologically active components, which display potent paralytic, cytotoxic, and cytolytic effects toward lepidopteran and dipteran hosts. The current study was undertaken to investigate if parasitism and/or envenomation by P. turionellae affects the frequency of apoptotic and necrotic hemocytes, hemocyte viability and mitotic indices in Galleria mellonella L. (Lepidoptera: Pyralidae) pupae and larvae. Our study indicates that parasitism and experimental envenomation of G. mellonella by P. turionellae resulted in markedly different effects on the ratio of apoptotic hemocytes circulating in hemolymph depending on the host developmental stages. The ratio of early and late apoptotic hemocytes increased in G. mellonella pupae and larvae upon parasitization and at high doses of venom when compared to untreated, null and Phosphate Buffered Saline (PBS) injected controls. In contrast, an increase in necrotic hemocytes was only observed in parasitized pupae at 24 h and no difference was observed in larvae. The lowest hemocyte viability values were observed with pupae as 69.87%, 69.80%, and 72.47% at 4, 8, and 24 h post‐parasitism. The ratio of mitotic hemocytes also decreased in pupae and larvae upon parasitization and at high doses of venom. Staining of hemocytes with annexin V‐FITC revealed green fluorescent ‘halos’ along the plasma membranes of venom treated cells within 15 min following exposure to venom. By 1 h post‐venom – treatment, the majority of hemocytes displayed binding of this probe, indicative of early stage apoptosis. These same hemocytes also displayed a loss of plasma membrane integrity at the same time points as evidenced by accumulation of propidium iodide in nuclei.     

Nutritional ecology of the interaction between larvae of the gregarious ectoparasitoid, Muscidifurax raptorellus (Hymenoptera: Pteromalidae), and their pupal host, Musca domestica (Diptera: Muscidae)

In this study we examined the relationship between clutch size and parasitoid development of Muscidifurax raptorellus (Hymenoptera: Pteromalidae), a gregarious idiobiont attacking pupae of the housefly, Musca domestica (Diptera: Muscidae). Host quality was controlled in the experiments by presenting female parasitoids with hosts of similar size and age. This is the first study to monitor the development of a gregarious idiobiont parasitoid throughout the course of parasitism. Most female wasps laid clutches of one to four eggs per host, although some hosts contained eight or more parasitoid larvae. In both sexes, parasitoids completed development more rapidly, but emerging adult wasp size decreased as parasitoid load increased. Furthermore, the size variability of eclosing parasitoid siblings of the same sex increased with clutch size. Irrespective of clutch size, parasitoids began feeding and growing rapidly soon after eclosion from the egg and this continued until pupation. However, parasitoids in hosts containing five or more parasitoid larvae pupated one day earlier than hosts containing one to four larvae. The results are discussed in relation to adaptive patterns of host utilization by gregarious idiobiont and koinobiont parasitoids.     

Two different life-history strategies determine the competitive outcome between Dirhinus giffardii (Chalcididae) and Pachycrepoideus vindemmiae (Pteromalidae), ectoparasitoids of cyclorrhaphous Diptera

Dirhinus giffardii Silvestri and Pachycrepoideus vindemmiae Rondani are solitary parasitoids attacking puparia of many cyclorrhaphous flies. They are not typical ectoparasitoids, as they feed on host pupae within puparia that develop from the exoskeleton of host larvae. Dirhinus giffardii did not kill its host until the parasitoid egg developed into a larva, while P. vindemmiae permanently paralysed its host at the time of oviposition. As a result, ovipositing into a young host puparium (< 1 day old) in which the host pupa has not yet fully formed resulted in complete death of offspring in P. vindemmiae, but D. giffardii, although suffering higher mortality than in older host puparia, still showed a level of successful development. In a choice experiment, both parasitoids preferred to attack 2- to 3-day-old puparia in which the host pupae had fully formed, rather than 1-day-old host puparia. Pachycrepoideus vindemmiae always prevailed in competition because it injected venom that not only paralysed the host, but also caused the death of D. giffardii larvae in multi-parasitized hosts. Dirhinus giffardii preferred to attack unparasitized hosts rather than hosts previously parasitized by P. vindemmiae, while P. vindemmiae did not show a preference between unparasitized hosts and hosts previously parasitized by D. giffardii.     

Parasitoid increases survival of its pupae by inducing hosts to fight predators

Many true parasites and parasitoids modify the behaviour of their host, and these changes are thought to be to the benefit of the parasites. However, field tests of this hypothesis are scarce, and it is often unclear whether the host or the parasite profits from the behavioural changes, or even if parasitism is a cause or consequence of the behaviour. We show that braconid parasitoids (Glyptapanteles sp.) induce their caterpillar host (Thyrinteina leucocerae) to behave as a bodyguard of the parasitoid pupae. After parasitoid larvae exit from the host to pupate, the host stops feeding, remains close to the pupae, knocks off predators with violent head-swings, and dies before reaching adulthood. Unparasitized caterpillars do not show these behaviours. In the field, the presence of bodyguard hosts resulted in a two-fold reduction in mortality of parasitoid pupae. Hence, the behaviour appears to be parasitoid-induced and confers benefits exclusively to the parasitoid.     

Does sex-biased dispersal account for the lack of geographic and host-associated differentiation in introduced populations of an aphid parasitoid?

Host recognition and use in female parasitoids strongly relies on host fidelity, a plastic behavior which can significantly restrict the host preferences of parasitoids, thus reducing the gene flow between parasitoid populations attacking different insect hosts. However, the effect of migrant males on the genetic differentiation of populations has been frequently ignored in parasitoids, despite its known impact on gene flow between populations. Hence, we studied the extent of gene flow mediated by female and male parasitoids by assessing sibship relationships among parasitoids within and between populations, and its impact on geographic and host‐associated differentiation in the aphid parasitoid Aphidius ervi. We report evidences of a high gene flow among parasitoid populations on different aphid hosts and geographic locations. The high gene flow among parasitoid populations was found to be largely male mediated, suggested by significant differences in the distribution of full‐sib and paternal half‐sib dyads of parasitoid populations.     

A chalcid wasp acts chiefly as a hyperparasitoid by mostly using small uncommon hosts

Although ovipositing insects may predominantly use resources that lead to high offspring quality, exceptions to this rule have considerably aided understanding of oviposition decisions. We report the frequency of host species use by a solitary facultative hyperparasitoid, Brachymeria subrugosa Blanchard (Hymenoptera: Chalcididae). In our samples, the wasp attacks the large pupae of the moth Gonioterma indecora Zeller (Lepidoptera: Elachistidae), as well as the considerably smaller, and rarer, pupae of two of its other parasitoids. Consistent with conditional sex allocation models, the wasp produced mainly female offspring on the largest (moth) host, an unbiased sex ratio on the middle‐sized (parasitoid) host, and only males on the smallest (parasitoid) host. Adult offspring size was correlated with the size of the host attacked. These features strongly suggest that the two smaller, primary parasitoid, hosts produce lower‐quality offspring. Despite being more common, the proportion of hosts from which parasitoids emerged was lowest (14%) on the largest host species, and highest on the rarer middle‐sized (34%) and smallest (30%) hosts. This suggests that costs or constraints on attacking high‐quality primary hosts may be a selective force favouring the evolution of hyperparasitism.     

寄主大小及寄生顺序对蝇蛹佣小蜂寄生策略的影响

寄主大小模型认为寄生蜂后代性比与寄主大小相关,寄生蜂倾向于在大寄主上产出更多雌性后代,在小寄主上产出更多雄性后代.探讨了以家蝇蛹为寄主时,蝇蛹佣小蜂后代产量和性比变化;单次寄生情况下,寄主大小及寄生顺序对寄生蜂后代性比等影响.结果表明,蝇蛹佣小蜂的产卵期为(8.93±3.34)d,单头雌蜂能产雌性后代(34.11±16.34)头和雄性后代(11.04±8.87)头,且雄性百分比为0.24±0.11.随成蜂日龄的增大,寄生蜂产生雄性后代的比率显著增加.蝇蛹佣小蜂在寄生家蝇蛹时,会优先选择寄生个体较大的蛹;在单次寄生的情况下,蝇蛹佣小蜂倾向于在较大的家蝇蛹内产出更多的雌性后代.     

家蝇蛹和果蝇蛹繁育的蝇蛹金小蜂对果蝇蛹的寄生比较

【目的】蝇蛹金小蜂Pachycrepoideus vindemmiae(Rondani)是杨梅园等果园果蝇类害虫蛹期常见寄生蜂种类,在对果蝇类害虫的生物防治上具有重要价值。本文旨在探讨使用家蝇蝇蛹为替代寄主繁育蝇蛹金小蜂的方法。【方法】探讨分别以家蝇蛹和果蝇蛹繁育的蝇蛹金小蜂对家蝇和果蝇蝇蛹的选择性,并比较了在两种寄主上繁育的蝇蛹金小蜂在大小、寿命、产卵期、后代产量和性比等方面的差异。【结果】结果表明与果蝇蛹相比,家蝇蛹明显较大,在家蝇蛹上发育的蝇蛹金小蜂后代个体也明显较大;家蝇蛹和果蝇蛹发育的寄生蜂雌蜂寿命为(13.4±4.11)和(3.94±2.49)d、产卵期分别为(11.4±4.11)和(3.13±2.42)d、单头雌蜂后代雌蜂数量分别为(34.31±31.83)和(7.88±3.58)头,在家蝇蛹上繁育的寄生蜂明显具有较长的寿命和产卵期、更多的雌雄蜂后代数量;在对家蝇蛹和果蝇蛹的选择上,繁育自家蝇和果蝇的蝇蛹金小蜂雌蜂选择频率的差异不大。【结论】利用家蝇蛹繁殖的蝇蛹金小蜂在寄生果蝇蛹时具有更大优势,在繁殖蝇蛹金小蜂控制杨梅园等果蝇的为害时,可以选择家蝇蛹作为替代寄主。     

Deadly venom of Asobara japonica parasitoid needs ovarian antidote to regulate host physiology

Asobara japonica (Braconidae) is an endophagous parasitoid developing in Drosophila larvae. The present study shows that A. japonica was never encapsulated in Drosophila melanogaster, and that it caused an overall inhibition of the host encapsulation reaction since injected foreign bodies were never encapsulated in parasitized hosts. Both the number of circulating hemocytes and the phenoloxidase activity decreased in parasitized larvae, and the hematopoietic organ appeared highly disrupted. We also found that A. japonica venom secretions had atypical effects on hosts compared to other braconid wasps. A. japonica venom secretions induced permanent paralysis followed by death of D. melanogaster larvae, whether injected by the female wasp during an interrupted oviposition, or manually injected into unparasitized larvae. More remarkably, these effects could be reversed by injection of ovarian extracts from female wasps. This is the first report that the venom of an endophagous braconid parasitoid can have a deadly effect on hosts, and moreover, that ovarian extracts can act as an antidote to reverse the effects of the wasp's venom. These results also demonstrate that A. japonica secretions from both venom gland and ovary are required to regulate synergistically the host physiology for the success of the parasitoid.