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.     

Host-feeding and egg maturation byPachycrepoideus vindemiae

Pachycrepoideus vindemiae Rondani (Hymenoptera: Pteromalidae) is a facultative hyperparasitoid ofDrosophila parasitoids in Europe. FemaleP. vindemiae host-feed from the same hosts into which they lay eggs and this enables them to mature additional eggs.P. vindemiae females were allowed to host-feed from puparia containingDrosophila melanogaster Meigen (Diptera: Drosophilidae) pupae or pupae ofAsobara tabida Nees (Hymenoptera: Braconidae). Wasps which had host-fed carried significantly more eggs; the species of host which was fed from had no significant effect on the number of mature eggs in the ovaries. Host-feeding caused no significant reduction in the size of the emerging offspring.P. vindemiae were allowed to forage over patches containing different frequencies of the two host species. No significant oviposition preference was found but there were marked host-feeding preferences which were affected by the age of the host pupae. It is suggested that these preferences were due to the physical nature of the hosts which were fed from.     

Pupal parasitoid attack influences the relative fitness of Drosophila that have encapsulated larval parasitoids

1. The evolution of host resistance to parasitoid attack will be constrained by two factors: the costs of the ability to defend against attack, and the costs of surviving actual attack. These factors have been investigated using Drosophila melanogaster and its parasitoids as a model system. The costs of defensive ability are expressed as a trade-off with larval competitive ability, whereas the costs of actual defence are exhibited in terms of reduced adult fecundity and size.
2. The costs of actual defence may be ameliorated by the host-choice decisions made by Pachycrepoideus vindemiae , a pupal parasitoid. If larvae that have successfully encapsulated a parasitoid develop into poorer quality hosts, then these may be rejected by ovipositing pupal parasitoids.
3. Pupae developing from larvae that have encapsulated the parasitoid Asobara tabida are smaller and have relatively thinner puparia. Thinner puparia are likely to be associated with a reduction in mechanical strength and possibly with a decrease in desiccation tolerance.
4. Pachycrepoideus vindemiae that develop in capsule-bearing pupae are smaller than those that emerge from previously unattacked hosts. This supports the prediction that ovipositing female P. vindemiae should avoid attacking capsule-bearing hosts. However, in choice experiments with 1-day-old pupae, P. vindemiae females oviposited preferentially in hosts containing a capsule, whereas there was no preference found with 4-day-old hosts. This appears to be a maladaptive host choice decision, as the female pupal parasitoids are preferentially attacking hosts that will result in a reduction of their own fitness.
5. The increased likelihood of attack by a pupal parasitoid is another cost of actual defence against larval parasitoid attack.     

Host exploitation and contest behavior in a generalist parasitoid partially reflect quality of distinct host species

Information use determines parasitoid adaptive behavior in general, and host specialization or fitness in specific. Information regarding host suitability could affect sex allocation behavior, host exploitation, or aggressiveness in dyadic contests. In this paper, we relate aggressiveness of the pupal parasitoid Pachycrepoideus vindemmiae (Hymenoptera: Pteromalidae) with sex allocation and host exploitation when presented with different host species. More specifically, we presented parasitoids with puparia of five different Dipteran species: Drosophila melanogaster (Drosophilidae), Musca domestica (Muscidae), Anastrepha obliqua, Anastrepha fraterculus, and Ceratitis capitata (Tephritidae). Puparia of above species greatly varied in size and volume, were parasitized to differing extent and had varying fitness implications for P. vindemmiae. Using a composite measure of selected fitness currencies (i.e., parasitism level, offspring size, longevity and sex ratio), we typified D. melanogaster and A. obliqua as ‘low quality’ hosts for P. vindemmiae while puparia of C. capitata and A. fraterculus were considered of ‘high quality’. In contest dyads, female aggressiveness and host exploitation behavior differed between host species. Wasps exhibited highest frequencies of antennal striking and rival pursuit, and high degrees of puparium mounting, antennating and probing on C. capitata. Antennal striking frequency however was equally high on ‘low quality’ hosts such as D. melanogaster and A. obliqua. This work shows that a generalist parasitoid such as P. vindemmiae assesses host quality when confronted with hosts of differing species, size or nutritional suitability and employs such to define sex allocation, host exploitation, and contest behavior. However, contest and exploitation behavior only partially indicate host quality and broader parasitoid fitness implications. This work has further implications for parasitoid mass rearing and use of P. vindemmiae for biological control of Dipteran pests.     

Performance of Two Fruit Fly (Diptera: Tephritidae) Pupal Parasitoids (Coptera haywardi [Hymenoptera: Diapriidae] and Pachycrepoideus vindemiae [Hymenoptera: Pteromalidae]) under Different Environmental Soil Conditions

We evaluated the performance of Coptera haywardi (Ogloblin) (Diapriidae) and Pachycrepoideus vindemiae (Rondani) (Pteromalidae), both hymenopteran pupal parasitoids of Anastrepha spp. (Diptera: Tephritidae). Performance was studied by manipulating the following environmental conditions in the laboratory: (1) soil type, (2) soil moisture content, (3) soil compaction, and (4) depth at which pupae were buried in the soil. There were two experiments: in the first, exposure time of pupae was held constant and in the second, it varied. In the first experiment, C. haywardi was significantly more effective than P. vindemiae in parasitizing fly pupae. With exposure time held constant (36 h), only soil type and pupal burial depth were significantly related to parasitism rates. While P. vindemiae only parasitized pupae located on the soil surface, C. haywardi attacked pupae that were buried up to 5 cm deep, performing better in clayey than in loamy soil. In the second experiment, exposure time (24, 36, 48, and 72 h) had no significant effect on parasitism rates, but soil type did. P. vindemiae again only attacked pupae on the soil surface while C. haywardi was also able to parasitize pupae that were buried up to 5 cm deep. We conclude that C. haywardi represents a viable candidate to replace the environmentally unfriendly P. vindemiae in augmentative biological control programs against fruit flies.     

Parasitoid-induced mortality of house fly pupae by Pteromalid wasps in the laboratory

House fly, Musca domestica L., pupae were exposed to six species of pteromalid parasitoids, Muscidifurax zaraptor Kogan and Legner, M. raptor Girault and Sanders, M. raptorellus Kogan and Legner, Pachycrepoideus vindemiae (Rondani), Spalangia nigroaenea Curtis, and Urolepis rufipes Ashmead. Exposures were made for 48 h at six parasitoid-to-host ratios to measure the effect of parasitoid density on parasitoid-induced mortality (PIM) of hosts (excluding mortality as measured by parasitoid emergence). PIM was evident at all parasitoid-to-host ratios for all six species. Fly eclosion declined with a corresponding increase in the parasitoid-to-host ratio; the reverse was generally true for PIM. Parasitoid emergence increased initially with a corresponding increase in the parasitoid-to-host ratio to a point (depending on the parasitoid species), but then declined. The three Muscidifurax spp. and P. vindemiae exhibited similar behavior and generally avoided previously stung hosts until ovipositional restraints broke down at the higher parasitoid-to-host ratios. S. nigroaenea and U. rufipes exhibited little ovipositional restraint, resulting in a high proportion of PIM of hosts. Understanding factors that influence PIM will provide better evaluations of field releases of parasitoids to control flies and will aid in the development of the most economic procedures for large scale rearing of pteromalid parasitoids.     

Pupal and larval-pupal parasitoids (Hymenoptera) obtained fromAnastrepha Spp. andCeratitis capitata (Dipt.: tephritidae) pupae collected in four localities of Tucuman province,Argentina

Pupal and larval-pupal parasitoids were obtained from 5 % of the 1,413 tephritid puparia collected in four localities of the Tucumán province, Argentina, from April, 1991 to April, 1993.Ceratitis capitata (Wiedemann) was attacked byPachycrepoideus vindemmiae (Rondani) (Pteromalidae), a pupal parasitoid, andAganaspis pelleranoi (Brèthes) (Eucoilidae), a larval parasitoid.Anastrepha spp. were attacked byDoryctobracon areolatus (Szépligeti) (Braconidae), a larval parasitoid, and also byA. pelleranoi. Information about parasitism, percentage of emergence of tephritid species and pupal viability in different localities is provided.     

Survival of the parasitoidEncarsia formosa after treatment of parasitized greenhouse whitefly larvae with fungal spores ofAschersonia aleyrodis

The interaction between the entomopathogenic fungusAschersonia aleyrodis and the parasitoidEncarsia formosa on greenhouse whitefly as a host organism was studied, in particular, the survival of the parasitoid after treatment of parasitized hosts with fungal spores. The mean number of parasitized black pupae per parasitoid produced at 25°C was significantly reduced after spore treatment in the first three days following parasitization. Spore treatment four, seven or ten days after parasitization resulted in a mean number of parasitized pupae not significantly different from the number of black pupae in the control. The rather sudden change from low to high survival of parasitized hosts when treated with spores four days after parasitization in spite of high numbers of infected unparasitized larvae, coincided with the hatching of the parasitoid larva from the egg inside the host. Possible reasons for this decrease in susceptibility to infection after parasitoid egg hatch, such as induced changes in host cuticle or haemolymph, are discussed. Parasitoids emerged from treated hosts did not show differences in reproduction compared with parasitoids emerging from untreated hosts. Both natural enemeies of whitefly are compatible to a great extent.     

Effects of the Cry1Ac toxin of Bacillus thuringiensis on Microplitis mediator, a parasitoid of the cotton bollworm, Helicoverpa armigera

Interactions between the cotton bollworm, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae), its larval parasitoid Microplitis mediator (Haliday) (Hymenoptera: Braconidae), and the Cry1Ac toxin of Bacillus thuringiensis Berliner were evaluated under laboratory conditions. The growth of H. armigera larvae was delayed and its pupal rate and pupal weight decreased when they were fed on a diet containing Cry1Ac toxin. Due to the lowered growth rate of the host larvae, the time available for parasitization of H. armigera by M. mediator increased when the host larvae were reared on a diet containing Cry1Ac toxin at concentrations of 0.5, 1, 2, and 4 µg g^?1. The longevity of female and male parasitoids was not significantly affected when newly emerging wasps fed on honey solutions containing three different concentrations of Cry1Ac toxin (125, 250, and 500 µg ml^?1). When female parasitoids were fed on honey solutions containing Cry1Ac, their offsprings’ egg and larval development period, pupal weight, length of pupation, adult weight, and adult longevity did not change significantly in most of the treatments compared with controls. When the female parasitoids parasitized host larvae that had been fed on a diet containing 0.5, 1, 2, 4, and 8 µg g^?1 Cry1Ac toxin, their offsprings’ eggs and larvae were significantly delayed. Their pupal weight, adult weight, and adult longevity were also significantly less than controls.     

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.     

Role of Caterpillar Silk Thread in Location of Host Pupae by the Parasitoid <Emphasis Type="Italic">Diadromus pulchellus</Emphasis>

Diadromus pulchellus is a solitary ichneumonid parasitoid. Its only known host is the pupa of Acrolepiopsis assectella, a specialist herbivore of Allium species. D. pulchellus females parasitize A. assectella pupae within 48 h after the caterpillars spin their cocoon and begin to pupate. Having observed that the cocoon produced by the leek moth caterpillar stimulates parasitoid egg-laying and that caterpillar leaves a silk thread, we studied the hypothesis that silk thread might be involved in host-finding by the parasitoid. Behavioral tests showed that when D. pulchellus females encounter a host silk thread, they change directions, follow the thread, and quickly locate the host. These findings show that pupal parasitoids can use signals produced by their hosts at the developmental instar preceding the one that they parasitize.     

Effects of host age on the performance of >Diadromus collaris, a pupal parasitoid of >Plutella xylostella

The ichneumonid >Diadromus collaris(Gravenhorst) (Hymenoptera: Ichneumonidae) is amajor solitary, pupal endoparasitoid of thediamondback moth, >Plutella xylostella(Linnaeus) (Lepidoptera: Plutellidae).Experiments to examine parasitism of the hostpupae of different ages by the parasitoid wereconducted in the laboratory. >Diadromuscollaris preferred host pupae that were in thefirst half of their pupal development. Survivalfrom larva to adult, and size and parasitizingcapacity of the resultant female adultsdecreased dramatically as host pupal ageincreased. When ovipositions were made intohost pupae that were in the last quarter oftheir development, all parasitoids died beforeadult emergence. The performance of >D.collaris, as affected by host pupal age,agrees with the simple diet theory thatpredicts female wasps should select hosts ofhigher nutritional quality for oviposition.     

Host range testing of a prospective classical biological control agent against cabbage maggot,Delia radicum,in Canada

The introduction of a European natural enemy, Aleochara bipustulata L. (Coleoptera: Staphylinidae), is being considered for control of cabbage maggot, Delia radicum (L.) (Diptera: Anthomyiidae) in canola in Canada, and the host specificity of this pupal parasitoid must first be studied. Contemporary guidelines were used to select 18 species of Diptera to represent non-target species taxonomically related or ecologically similar to reported hosts of A. bipustulata, or beneficial species. No-choice tests were used to determine which of the 18 species are within A. bipustulata’s fundamental host range, and whether puparial structure or mass or duration of pupal development influence their acceptability and suitability as hosts. Five species were consistently suitable as hosts, and these were either relatively small or were taxonomically closely related to the target host. The probability that a puparium would be entered by a parasitoid larva was greatest for small puparia, but was unaffected by pupal duration. The probability of completing parasitoid development once a puparium was entered was influenced by both puparial mass and duration of pupal development. Pitfall traps to assess habitat associations caught A. bipustulata adults in a variety of crop habitats but none were caught in forests. Host range and habitat data are used to argue that there is little risk of parasitism to beneficial taxa. Non-target species taxonomically closely related to the target D. radicum or with small puparia may fall within the fundamental host range of A. bipustulata. However, risk to many of these species may be minimal because of the habitat preferences of the parasitoid and its cues for host-finding and recognition.     

Impact of spinosad on ichneumonid‐parasitized Choristoneura rosaceana larvae and subsequent parasitoid emergence

The impact of low levels of spinosad on the obliquebanded leafroller, Choristoneura rosaceana Harris (Lepidoptera: Tortricidae), and the koinobiont endoparasitoid, Apophua simplicipes Cresson (Hymenoptera: Ichneumonidae), was assessed when the parasitoid was in the larval stage within second‐ and fourth‐instar hosts. These are developmental stages that would be exposed to spring orchard treatments of the insecticide. Oral spinosad LC₅₀ levels for unparasitized obliquebanded leafroller hosts were <1% of the recommended orchard treatment levels. Apophua simplicipes survival was significantly reduced within parasitized spinosad‐treated second‐ and fourth‐instar larval hosts. Both the leafroller host and parasitoid were much more susceptible (ca. 65‐fold) to spinosad when larval hosts fed on spinosad‐treated leaf material as opposed to being treated topically. When hosts were exposed to extremely low doses of spinosad, a small percentage of parasitoids was able to survive to emerge as adults. These laboratory trials predict that applications of spinosad may reduce biological control of C. rosaceana populations by ichneumonid endoparasitoids developing within treated hosts.     

Seasonal phenology and stage-specific parasitism of the apple ermine moth, Yponomeuta malinellus Zeller, in Korea

The apple ermine moth, Yponomeuta malinellus Zeller (Lepidoptera: Yponomeutidae), is a tent caterpillar that feeds on Malus spp. in Korea. Populations of the moth in native areas appeared to be regulated by the assemblage of parasitoids. Phenological associations between host stages and parasitoids, susceptible stage(s) of the host for each parasitoid, and stage‐specific parasitism were studied. The egg larval parasitoid Ageniaspis fuscicollis (Dalman) had highest parasitism of first instar larvae (24%), with 14% parasitism of other larval stages. Dolichogenidea delecta (Haliday) was recovered from all larval instars with the highest parasitism rate of second instar larvae (20.1%), followed by 19.9% parasitism of mid‐larval hosts. Herpestomus brunicornis Gravenhorst was reared from second instar larvae through to pupal collection, and had the highest parasitism rate (29.9%) at the pupal stage. The larval pupal parasitoid Zenillia dolosa (Meigen) was recovered from mid‐larval to pupal stages with the highest parasitism rate (5.5%) occurring in third to fourth instar larvae. The host stages for developing A. fuscicollis completely overlap with those of D. delecta, and with those of H. brunicornis to some degree. A statistically significant negative correlation exists between A. fuscicollis and these dominant parasitoids, indicating competitive interaction within the host.     

Influence of parasitism and soil compaction on pupation of the green bottle fly,Lucilia sericata

The influence of parasitoids and soil compaction on pupation behavior of blow flies was examined in a host–parasitoid system involving Lucilia sericata (Meigen) (Diptera: Calliphoridae) and Nasonia vitripennis (Walker) (Hymenoptera: Pteromalidae). Larvae of L. sericata were introduced to containers with soil of different compaction levels, with or without parasitoids. Although females of N. vitripennis did not significantly affect the pupation depth of L. sericata, they increased the rate of pupal development by 15.0–23.7 h at 28.4 ± 1.2 °C, and increased the clumping of puparia. Pupation depth of L. sericata was negatively related to soil compaction; mean depth of pupation was 4.4 cm in uncompacted soil and 0.5 cm in high‐compaction soil. In high‐compaction soil, pupal development increased by 10.5–18.8 h at 25.2 ± 0.3 °C, and puparia were clumped. These results provide a framework for locating puparia in forensic investigations and releasing appropriate parasitoids for biological control of blow flies.     

Reproductive performance of Nesolynx thymus (Hymenoptera: Eulophidae), in relation to age of Musca domestica (Diptera: Muscidae)

An investigation was undertaken to record the influence of host age on the reproductive performance of Nesolynx thymus (Hymenoptera:Eulophidae). This is an indigenous, gregarious, ecto-pupal parasitoid of certain dipteran insects, including the tachinid fly, Exorista bombycis (Louis) which is a well-known endo-larval parasitoid of the silkworm, Bombyx mori. Each gravid N. thymus female was allowed to parasitise 1–4-day-old puparia of Musca domestica L. for 2 days at a parasitoid–host ratio of 1:20. The parasitised host puparia were observed for progeny recovery, sex ratio, female longevity and fitness (adult size). In addition, reproductive performance of the parasitoid progeny was assessed by allowing its females to parasitise for 2 days, 3-day-old puparia of E. bombycis at a parasitoid–host ratio of 1:4. There was a significant negative correlation between host age and parasitisation rate, parasitoid developmental duration, sex ratio and female longevity while the correlation was positive between host age and parasitoid recovery per host puparium. Similarly, negative correlation was observed between host age and morphometric parameters (body length, head width and wing span of male and female and length and width of female abdomen) of the progeny adults. Host age did not have any impact on the reproductive performance of progeny adults when allowed to parasitise puparia of E. bombycis.     

瓜实蝇2种蛹寄生蜂生防潜能比较

[目的] 比较研究蝇蛹俑小蜂与蝇蛹金小蜂对瓜实蝇的控制潜能。[方法] 采用非选择性实验测定蝇蛹俑小蜂与蝇蛹金小蜂对瓜实蝇蛹的寄生效能、繁殖能力,并研究覆土厚度对2种寄生蜂寄生效能的影响。[结果] 2种寄生蜂对瓜实蝇的寄生率无显著性差异,但蝇蛹金小蜂的平均单雌产后代数比蝇蛹俑小蜂的多,分别为30和23头。土壤厚度显著影响2种寄生蜂的寄生效能,随着土壤厚度的增加,2种寄生蜂对瓜实蝇蛹的寄生率均显著下降,但蝇蛹金小蜂的寄生率下降更为迅速;蝇蛹俑小蜂最深可寄生8 cm土壤下的瓜实蝇蛹,而蝇蛹金小蜂在土壤厚度达到3 cm时就不能完成寄生。[结论] 蝇蛹俑小蜂较蝇蛹金小蜂更适合应用于瓜实蝇蛹的生物防治。