Limited protection of the parasitoid Pachycrepoideus vindemiae from Drosophila suzukii host‐directed spinosad suppression

Laboratory trials were conducted to determine whether the spotted wing drosophila, Drosophila suzukii (Matsumura) (Diptera: Drosophilidae), puparium can provide an effective physical barrier to protect immature stages of the pupal parasitoid Pachycrepoideus vindemiae (Rondani) (Hymenoptera: Pteromalidae) from spinosad treatments. Spinosad insecticides are currently an important suppression strategy for D. suzukii in organically managed fruit orchards although they are well known to cause mortality in hymenopteran parasitoids. High adult P. vindemiae female mortality (83%) occurred within 24 h of exposure to D. suzukii pupae treated with 10 mg a.i. l^?1 spinosad and female parasitoids did not avoid the pupae treated with similar low levels of spinosad in choice tests that included untreated pupae. Pachycrepoideus vindemiae develops as an idiobiont ectoparasitoid on host fly pupa within the sclerotized host puparium. Significant P. vindemiae survival and emergence was recorded when parasitized D. suzukii puparia were exposed to field treatment levels of spinosad; however, the parasitoid survival was dependent on the time of the spinosad treatment of the host post‐parasitization. Significant parasitoid survival occurred when the host puparia were treated at 2 weeks when the parasitoid was in the pupal stage but did not occur when the host puparia were treated at 1 week post‐parasitization, when the parasitoids were still in a larval stage. The parasitoid adults consumed or otherwise came in contact with residual degrading spinosad when they exited the treated host, and consequently high and low adult parasitoid mortality occurred when the adults emerged from puparia treated at 2 and 1 week(s), respectively. Our study indicates that generally the integration of P. vindemiae parasitism into a sustainable D. suzukii management program is not compatible with spinosad treatments, although P. vindemiae in the pupal stage inside sclerotized host puparia appear to be minimally impacted by spinosad treatments, provided that the spinosad degrades before parasitoid emergence.     

Behavioural responses to dimethyl disulphide by Aleochara bilineata and Aleochara bipustulata

Adult Aleochara bipustulata L. and Aleochara bilineata Gyllenhal (Coleoptera: Staphylinidae) are predatory on immature stages of cabbage root fly Delia radicum (L.) (Diptera: Anthomyiidae). Larvae of the two Aleochara are parasitoids of D. radicum pupae. Female Aleochara lay eggs near D. radicum puparia; the newly‐hatched Aleochara larvae enter puparia and consume the contents. Delia radicum‐infested roots of brassicas give off dimethyl disulphide (DMDS). In the field, DMDS attracts adult Aleochara to pitfall traps but does not enhance the biological control of D. radicum. In the present study, we investigate the behavioural responses of the Aleochara to DMDS in still air, as well as in moving air in a Y‐tube olfactometer, and also investigate the influence of DMDS on host selection. In larvae of both Aleochara species, DMDS induces a restricted‐area search in still air, resulting in elevated frequencies of attack of D. radicum puparia close to a source of DMDS. In the olfactometer, newly‐emerged virgin adults of both sexes of both Aleochara species choose alternatives to DMDS, older recently‐mated females are attracted to DMDS, and older males and older mate‐deprived females show no preference. Mating status of males determines the switch of their response to DMDS from avoidance to indifference. We conclude that DMDS is an important cue for host‐finding, although other cues are involved in mate‐finding. We discuss the implications for use of DMDS to enhance D. radicum mortality and for parasitism of nontarget species if A. bipustulata is introduced to Canada for biological control of D. radicum.     

Costs of reproduction and geographic variation in the reproductive tactics of the mosquito Aedes triseriatus

Intraspecific host discrimination is widespread in solitary parasitoids whose adult females forage for and evaluate host suitability, whereas interspecific discrimination is less common. In some parasitoid species, mostly Diptera and Coleoptera, the larva performs the last step of host searching. It has been suggested that host discrimination will rarely occur in such host-seeking larvae because their low mobility results in a low host encounter rate. We determined the extent to which the larvae of Aleochara bilineata Gyllenhal (Coleoptera: Staphylinidae), a solitary parasitoid of aggregated Diptera pupae: (1) discriminated between unparasitized hosts and hosts parasitized by conspecifics; (2) used semiochemical cues to discriminate; (3) were influenced by life expectancy, presence of conspecifics and host availability in their host acceptance decision; and the extent to which (4) A. bilineata and A. bipustulata L., a species exploiting the same hosts and occurring sympatrically, showed interspecific host discrimination. A. bilineata larvae were able to discriminate between unparasitized hosts and hosts parasitized by conspecifics in a choice experiment. Such behavior has never previously been described for a coleopteran parasitoid or for a parasitoid species whose larvae perform host searching. Host discrimination in this species was not based on the presence of visual or tactile cues (e.g., entrance holes) but rather on chemical cues. The life expectancy of A. bilineata larvae was significantly shorter in the presence than in absence of hosts, and older larvae had lower parasitism success than young larvae in a 24-h experiment. However, the host acceptance decision of A. bilineata larvae was not influenced by larval age or the presence of conspecifics when the ratio of hosts per larva was greater than or equal to 1. When hosts were scarce, the degree of superparasitism increased significantly with the number of foraging conspecifics and the age of the larvae. Both species of Aleochara showed intra- and interspecific host discrimination in a choice experiment. In contrast to A. bipustulata, A. bilineata larvae more frequently parasitized hosts parasitized by A. bipustulata than those parasitized by conspecifics. We suggest that host discrimination will be frequent in solitary parasitoids with host-seeking larvae when hosts are aggregated. Received: 4 June 1998 / Accepted: 1 September 1998     

Diapausing pupae of the flesh fly Sarcophaga crassipalpis (Diptera: Sarcophagidae) are more resistant to inoculative freezing than non-diapausing pupae

The resistance of diapausing (overwintering) and non‐diapausing (summer) Sarcophaga crassipalpis (Diptera: Sarcophagidae) pupae to inoculative freezing was examined. Although both types of pupae resisted inoculative freezing after 24‐h submergence in water, diapausing pupae were overall significantly more resistant than non‐diapausing pupae. Exposing the thin pupal cuticle by removing the ends of the puparial case eliminated the capacity of both pupal types to resist inoculative freezing, indicating that resistance to inoculative freezing resides with the puparium. Pupae submerged in surfactant solution were significantly less resistant to inoculative freezing than those submerged in water. Furthermore, the puparial water content of pupae submerged in surfactant solution was significantly greater than that of puparia from pupae submerged in water. Surfactant may have promoted inoculative freezing by facilitating the spread of water over the surface of and into the puparium, thereby creating bridges between external ice and pupal body fluids. Extracting puparial surface lipids with chloroform/methanol (2 : 1, v:v) decreased the resistance of non‐diapausing pupae to inoculative freezing but did not significantly affect that of diapausing pupae. This finding indicates that the puparium of diapausing pupae contains protection against inoculative freezing separate from its surface lipids. This barrier may be important in protecting the freezing‐intolerant overwintering pupae against inoculative freezing within their soil hibernaculum.     

Aleochara suffusa andA. bilineata (Col.: Staphylinidae) as parasitoids of brassica root flies in northern Norway

A sample ofDelia puparia collected in late autumn from a brassica field at Tromsø, northern Norway, was investigated to study the level of parasitism byAleochara. BothA. suffusa andA. bilineata were reared from puparia of the cabbage root fly,Delia radicum, and the bean seed flies,D. florilega and/orD. platura. Only two specimens ofA. bilineata emerged from puparia of the turnip root fly,D. floralis. BothAleochara species hibernated in the larval state and both pupated inside the host puparium. Most specimens ofA. suffusa emerged from small hosts (D. florilega/D. platura), whereas the majority of A.bilineata emerged from host species of larger size (D. radicum/D. floralis). The time to develop from first instar larva to adult was similar for bothA. suffusa andA. bilineata. Parasitoids developing in large hosts emerged later than those in small hosts, the delay being the same for both species ofAleochara.     

Life history comparison between two competitive Aleochara species in the cabbage root fly, Delia radicum: implications for their use in biological control

This study evaluates the efficacy of Aleochara bilineata Gyll and Aleochara bipustulata L. (Coleoptera: Staphylinidae) as biological control agents against the cabbage root fly, Delia radicum L. (Diptera: Anthomyiidae). Biological and demographic characters are documented and comparisons made between the two species. The following results were obtained:(1) The reproductive potential and longevity of A. bipustulata females are significantly higher than those of A. bilineata. These differences are correlated with the biology and ecology of the hosts of both species.(2) Under laboratory conditions the rate of increase (r_m) of both staphylinids species is significantly higher than that of the pest and their major competitor Trybliographa rapae West. (Hymenoptera:Figitidae). This may indicate that A. bilineata and A. bipustulata can be effective biological control agents.(3) Aleochara bilineata appears to be the most interesting biological control agent against D. radicum, because of its higher rate of increase, higher host specificity and host acceptance, and a development time which is well synchronised with that of its host. With its higher competitive ability, a population of A. bilineata may increase even if competition occurs. However, A. bipustulata presents interesting biocontrol characteristics, but the best strategy may be only to use the potential of its natural populations.     

Stabilization of mineralized and sclerotized puparial cuticle of muscid flies

Calcium, magnesium and phosphorus are the major mineral elements in puparial exuviae of the face fly, Musca autumnalis, house fly, M. domestica and stable fly, Stomoxys calcitrans, but they are 20–50 times more prevalent in face fly than in the other two species that sclerotize the puparium. Carbon and nitrogen are approx. 5 times more abundant in house fly puparia than in face fly puparia. Face fly puparia contain two and three-fold less total amino acids than the house fly and stable fly, respectively. β-Alanine is a major amino acid in puparial cuticle of the house fly and stable fly, but it is absent in the face fly. There is no significant difference in glucosamine (chitin) content between the three species. Dopamine is the major catechol detected in face fly puparial cuticle while N-β-alanyldopamine (NBAD) is 10 to 15 times more prevalent than other catechols such as dopamine, N-acetyldopamine (NADA), 3,4-dihydroxyphenylalanine (DOPA) and 3,4-dihydroxyphenylacetic acid (DOPAC) in house fly and stable fly puparial cuticles. The latter two species have 75 to nearly 200 times higher levels of extractable catechols than the face fly. At the onset of pupariation, dopamine and NBAD attain nearly equivalent titres in puparial cuticles of face fly and house fly, respectively. Dopamine subsequently decreases more than 40-fold in the face fly as the cuticle becomes stabilized, while NBAD continues to accumulate in the house fly. The house fly covalently incorporates about 150 times more catechols in the puparium than does the face fly. The force required to fracture house fly and stable fly puparia is about three-fold greater than that required to fracture face fly puparia of comparable thickness. However, the face fly puparium attains a strength comparable to those of house fly and stable fly puparia by significantly increasing its thickness. These results demonstrate that dipterans use both catecholamines and minerals for stabilization of puparial cuticle with the house fly and stable fly relying primarily on sclerotization and the face fly on mineralization.     

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.     

Structure,organization, and response of a species-rich parasitoid community to host leafminer population dynamics

The parasitoid community dynamics of an agromyzid honeysuckle leafminer, Chromatomyia suikazurae (Agromyzidae, Diptera) were studied between 1981 and 1990 in a natural forest in Kyoto, Japan. The parasitoid fauna composed three koinobionts (all larval-pupal solitary parasitoids) and 22 idiodiont species (11 larval solitary, nine pupal solitary and one pupal gregarious). The parasitoid community was dominated by early-attacking oligophagous braconid koinobionts at early periods, but was gradually displaced by late-attacking polyphagous eulophid idiobionts. Accordingly, the diversity index of the parasitoid community peaked at an intermediate point in the intra-generational succession. The succeeding attack-in-waves by the late-attacking idiobionts greatly reduced not only the survival rates of early-attacking parasitoid larvae but also the survival rates of hosts. The density-dependence observed in the host pupal mortality was thought to result from density-dependent host-switching by a keystone polyphagous pupal idiobiont parasitoid, Chrysocharis pubens, whereas high host pupal mortality was potentially attained by an early-attacking koinobiont braconid. Supposed aggregation of polyphagous parasitoids at high host density resulted in intense within-host competition and in an increase of host-feeding attack, both of which contributed to low emergence rates of parasitoids at high host densities. Parasitoid emergence rates were also reduced at low host densities, probably by inter- and intra-specific hyperparasitism among oligophagous parasitoids for limited hosts. The regulation effects of the species-rich parasitoid community upon the host population dynamics are thought to derive from succeeding attack-in-waves by polyphagous late-attacking idiobionts, especially by the keystone species.     

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.     

Effects of parasitoid community structure upon the population dynamics of the honeysuckle leafminer,Chromatomyia suikazurae (Diptera: Agromyzidae)

Population dynamics of a leafminer,Chromatomyia suikazurae (Agromyzidae, Diptera) and its parasitoid community were studied for ten years at seven natural populations along an altitudinal gradient in Japan. This species which mines leaves of a forest shrub,Lonicera gracilipes (Caprifoliaceae), was attacked by 25 hymenopterous parasitoid species. Annually, the parasitoid community structure varied less within a population than among populations. The seven parasitoid communities were clustered into three groups corresponding to the altitudinal gradient: (a) lowland communities dominated by late-attacking, generalist pupal idiobiont eulophids and with highest species diversity, (b) hillside communities dominated by an early-attacking, specialist larval-pupal koinobiont braconid and (c) highland communities dominated by an early-attacking, generalist larval idiobiont eulophid. Annual changes of the host larval densities among the local populations were largely synchronous rather than cyclic. Among these populations, host density levels and mortality patterns greatly varied. By analyzing these inter-populational differences of host mortality patterns, the following conclusions were drawn: (1) The host mortality patterns were determined by the host utilization patterns of the locally dominant species. (2) The host pupal mortality but not larval mortality was related to species diversity but not to species richness itself of each parasitoid community. (3) Density dependence was detected only in pupal mortality at a lowland population dominated by late-attacking pupal parasitoids. These results suggest that interspecific interactions of parasitoids add additive effects to host population dynamics dissimilarly among local populations with different parasitoid communities.     

Some effects of low oxygen partial pressures on the development of Calliphora vomitoria;

The influence of wet conditions and low pO₂ on the survival and development of non-feeding final instar larvae and puparia of Calliphora vomitoria has been investigated. The larvae delay the formation of the puparium in wet conditions in air and in dry or wet conditions in 10 and 5% oxygen. This may be related to the susceptibility of the newly formed puparia to oxygen shortage. The pupal respiratory horns play an important part in maintaining O₂ uptake when the puparia are surrounded by particles covered with a film of water but are not involved in aiding survival in low pO₂. Zero age puparia are killed by a 2 day exposure to 10% O₂ but later stages can continue to develop in this gas. Fifty per cent of the 0, 1 and 9 day old puparia are killed by about a 12 hr exposure to 1% O₂ whereas 50 per cent of the 2 to 8 day old puparia can survive over 1·5 days exposure to this gas. Development, as measured by respiration rates and the timing of the emergence of the adults, is delayed by 1% O₂ by the amount of time that the insects spend in that gas. However, the first phase of elongation of the pharate adult longitudinal flight muscle, occurring between the third and fourth day of puparial life, is only slightly slowed down in 1% O₂. The variations in susceptibility to 1% O₂ and the growth of the muscles are discussed in relation to published accounts of protein synthesis in the puparium.     

Susceptibility of Delia radicum to steinernematid nematodes

Isolates of different Steinernema species (S. affine, S. bicornutum, S. feltiae and Steinernema C1) were used in mortality assays with third instar larvae of Delia radicum (L.) (Diptera: Anthomyiidae). The nematode isolates had been obtained by baiting soil regularly grown with cabbage. One isolate (S. feltiae) was the result of a natural infection of a D. radicum puparium. The highest mortality (77%) was obtained with an isolate of S. feltiae (DK1). The isolate DK1 was also used in tests with all larval stages of D. radicum. Mortality around 60% was observed for second and third instar larvae, while first instar larvae showed very low or no susceptibility. Maximum mortality of second and third instar larvae was reached applying only 25 nematodes per larva. Observations of larvae that pupated revealed that some of these puparia contained nematodes. Experiments with hatching puparia showed that a high proportion was infected by nematodes if the flies were prevented from leaving nematode-containing soil. In addition to mortality, the ability of the nematodes to successfully reproduce in the insects was studied. It was found that the species S. feltiae and S. bicornutum reproduced in D. radicum larvae and adults with S. feltiae being the most successful.     

Factors determining the structure and diversity of parasitoid complexes in tephritid fruit flies

Summary The relative importance of phylogenetic affinity of hosts versus their ecological characteristics in determining the composition of their parasitoid complexes was examined using the parasitoid complexes of six species of frugivorous fruit flies from Central Europe. The hosts were four Rhagoletis and two other trypetine species, ranging in their relatedness from host races to members of different genera. They also differed in ecological characteristics, utilizing host plants of three different families, and developing either as pulp- or seedfeeders inside the host fruit. These features made it feasible to test the following pair of hypotheses. The ecological hypothesis predicts that ecological traits such as host-plant and fruit fly phenologies and host-fruit texture should be more important for the composition of parasitoid complexes than the taxonomic relatedness of the fly species. Assuming that ecological relationships do not parallel phylogenetic ones, the alternative phylogenetic hypothesis predicts the opposite. In fruit and soil samples, taken between 1983 and 1989, three guilds of parasitoids comprising 20 species were found: guild 1 — koinobiotic larval parasitoids (e.g. Opius spp., which attack the host larvae but develop inside the host puparia); guild 2 — idiobiotic larval parasitoids (e.g. Pteromalus spp., which consume the host larvae at once); and guild 3 — idiobiotic puparium parasitoids (e.g. Phygadeuon spp.). Although some results support the phylogenetic hypothesis, the majority of results support the ecological hypothesis.     

Influence of a bimodal emergence strategy of a Dipteran host on life-history traits of its main parasitoids

Abstract. 1. Among a great diversity of other strategies, insects have evolved polymodal emergence patterns that can increase survival in the face of annual variations in environmental conditions. Delia radicum L. (Diptera: Anthomyiidae) is a polyvoltine pest that attacks several cultivated cruciferous species. At the time of emergence, most populations show a polymodal emergence of type A (i.e. all individuals that enter diapause in the same year terminate diapause the following growing season, and exhibit a bimodal emergence curve). This results in the occurrence of two sympatric phenotypes, early and late, which differ by the timing of adult emergence in both diapausing and non‐diapausing generations. 2. In Brittany, D. radicum pupae can be heavily parasitised by three parasitoids, Aleochara bilineata Gyll. (Coleoptera: Staphylinidae), Aleochara bipustulata L., and Trybliographa rapae (Hymenoptera: Eucoilidae). As in all parasitoids species, the successful development of both Aleochara species and T. rapae larvae depends mainly on the amount and quality of the food provided by the host. 3. The relationship between early and late host phenotype and (i) the parasitism efficiency, (ii) emergence patterns, and (iii) host selection behaviour were investigated for the three parasitoid species. 4. Depending on parasitoid species and their different parasitism and development mode, the results reveal that host phenotype can influence (i) survival and development time in T. rapae, and (ii) survival in Aleochara species. Aleochara larvae did not appear to discriminate between early and late host pupae on the basis of phenotype, but rather selected them according to their developmental stage. Furthermore, it was discovered that the same phenological strategy occurred in T. rapae and in D. radicum. However, for D. radicum the results indicate that such a strategy has a cost as the longer development time of late host pupae results in a longer period of time favourable for parasitism.     

Parasitoid assemblages of soybean defoliator Lepidoptera in north-western Buenos Aires province, Argentina

1 The objective of this study was to examine the structure of parasitoid assemblages attacking soybean defoliator Lepidoptera in north-western Buenos Aires province, Argentina. 2 Through larvae sampling from 1992 to 1996, and laboratory data plus the known biology of the species recorded during the study, parasitoid species composition, richness, number of guilds per host species, and levels of parasitism, were determined. 3 Total species richness was 23, all species were primary endoparasitoids, and categorized as koinobionts. They belonged to Hymenoptera (11 species) and Diptera (12 species). Rachiplusia nu (Noctuidae) hosted the highest number of parasitoid species. 4 Four parasitoid guilds were recorded for R. nu (egg–prepupal endoparasitoid, early larval endoparasitoid, late larval endoparasitoid, and larval–pupal endoparasitoid); two for Spilosoma virginica (Arctiidae) (late larval endoparasitoid and larval–pupal endoparasitoid) and Colias lesbia (Pieridae) (early larval endoparasitoid and larval–pupal endoparasitoid); and one for Anticarsia gemmatalis (Noctuidae) and Loxostege biffidalis (Pyralidae) (early larval endoparasitoid). 5 Only four out of seven potential parasitoid guilds defined for Lepidoptera were recorded in a soybean agroecosystem located in north-western Buenos Aires province, suggesting that potential host niches were not totally utilized. 6 Soybean lepidopteran defoliators supported a mean species richness of 4.8 parasitoids, a result that is similar to that reported for exophytic hosts in the Neotropics. 7 Parasitoid assemblages from each host differed in species composition, richness, number of guilds, and levels of parasitism.     

A new host record forTachinaephagus zealandicus [Hym.: Encyrtidae]

Tachinaephagus zealandicus Ashmead was reared from puparia ofProtocalliphora n. sp. [Dip.], representing a new host record for this parasitoid. The habitat ofProtocalliphora is qualitatively different than those of all previously recorded hosts for this parasitoid.T. zealandicus has been imported from Australia and New Zealand and this record strengthens the belief that it has become established in California.     

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.     

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.     

Does host age affect progeny production and progeny fitness in Trichopria sp.?

The gregarious endoparasitoid Trichopria sp. (Hymenoptera: Diapriidae) is currently under evaluation for its potential to suppress the levels of parasitism in larvae of the silkworm Bombyx mori (Lepidoptera: Bombycidae) caused by the tachinid fly Exorista bombycis (Louis) (Diptera: Tachinidae) in the rearing houses of sericulture farmers in southern India. Parasitism by E. bombycis currently results in cocoon yield reductions of 10–20 %. Prior to the mass production and release of Trichopria sp., there is a need to understand the factors that affect progeny production and fitness. Within this framework, we have attempted to determine whether host age has an impact on the numbers of Trichopria sp. progeny produced and on the subsequent fitness of the adults of the wasp. Two day-old adult females of the parasitoid were allowed to parasitize day (D) 1, 3, 5, 7, and 9 puparia of E. bombycis at a ratio of 1:4 (wasp:host). After eclosion of the parasitoid adults, data on the rate of parasitism, developmental period, brood allocation, progeny production, sex ratio, female progeny longevity and adult size were recorded. The reproductive performance of the adult progeny was also recorded by allowing them to parasitize three day-old E. bombycis puparia. Host age was seen to have an effect on several of the parameters recorded, such that while the most progeny were produced by the youngest (D1) hosts, larger wasps emerged from older E. bombycis puparia. It was, however, apparent that all but the oldest hosts (D9) examined were able to support adequate parasitoid development. Further, only relatively minor impacts on progeny fitness were observed between wasps deriving from hosts of different ages. However, the results strongly indicate that optimal production and parasitoid performance will be obtained by using young hosts of less than three days old.