Ecological and morphological characteristics of endoparasitoids on Elcysma westwoodii (Vollenhoven) (Lepidoptera: Zygaenidae)

Six species of insect endoparasitoids were identified from Elcysma westwoodii, which is the most damaging lepidopteran pest of Prunus yedoensis. From Hymenoptera, two species were identified: a species in Braconidae and Charops striatus in Ichneumonidae. From Diptera, there were four species in Tachinidae: Compsilura concinnata, Exorista sp., Pales sp. and Tachinidae spp. The parasitic ratio was 4.86% (45 of 926 larvae). The hymenopterans were parasitic on 31 individuals of E. westwoodii (68.9%) and the dipterans were parasitic on 14 individuals (31.1%). It was found that parasitoids from the larvae of E. westwoodii were all either endoparasitoids or larval parasitoids. However, Exorista sp. of Tachinidae was found to be either a larval parasitoid or larval-pupal parasitoid. Additionally, all the identified parasitoids were solitary parasitoids, as only one parasite occurred in a larva of E. westwoodii. Because the larva of E. westwoodii eats and molts after it is parasitized, all the parasitoids were identified as koinobionts. There were no big differences in morphological characteristics and life histories between C. striatus and C. concinnata. However, for Exorista sp. and Pales sp., males took 3–5 days longer to emerge from their pupae and had remarkably longer body lengths than females.     

Incidence of turf-damaging white grubs (Coleoptera: Scarabaeidae) and associated pathogens and parasitoids on Kentucky golf courses

Root-feeding grubs (Coleoptera: Scarabaeidae) were sampled from damaged areas of 61 irrigated roughs on 32 Kentucky golf courses to determine species composition and natural enemy incidence, the first such survey in the United States' transitional turfgrass climatic zone. Masked chafers (Cyclocephala lurida Bland and C. borealis Arrow) and Japanese beetle (Popillia japonica Newman) accounted for ≈73 and 26% of grubs found in an autumn survey, with Cyclocephala spp. predominating at most sites, although mixed infestations were common. Only a few Phyllophaga spp., and no exotic species other than P. japonica were found. Cyclocephala spp. also predominated in seasonal and statewide surveys regardless of whether a course had cool- or warm-season grass fairways. Pathogenic bacteria, Paenibacillus and Serratia spp., and the autumn-active parasitoid Tiphia pygidialis Allen were the main enemies associated with Cyclocephala spp. Predominant enemies of P. japonica were Paenibacillus, Serratia, and Metarhizium spp. in autumn, and eugregarines, Stictospora sp. (probably S. villani Hays and Clopton) and Tiphia vernalis Rohwer in spring. Entomopathogenic nematodes and the microsporidian Ovavesicula popilliae Andreadis & Hanula were nearly absent in our samples. No predictive relationships were found between soil parameters and proportionate abundance of Cyclocephala or P. japonica, or with natural enemy incidence at particular sites. Although incidence of individual enemies was generally low (<20%; often <5%) in these point-in-time surveys, collectively and over their hosts' prolonged development they may take a significant toll on grub populations.     

Lack of lipogenesis in parasitoids: a review of physiological mechanisms and evolutionary implications

The ability of organisms to adapt to fluctuating food conditions is essential for their survival and reproduction. Accumulating energy reserves, such as lipids, in anticipation of harsh conditions, will reduce negative effects of a low food supply. For Hymenoptera and Diptera, several parasitoid species lack adult lipogenesis, and are unable to store excess energy in the form of lipid reserves. The aim of this review is to provide a synthesis of current knowledge regarding the inability to accumulate lipids in parasitoids, leading to new insights and prospects for further research. We will emphasize physiological mechanisms underlying lack of lipogenesis, the evolution of this adaptation in parasitoids and its biological implications with regard to life history traits. We suggest the occurrence of lack of lipogenesis in parasitoids to be dependent on the extent of host exploitation through metabolic manipulation. Currently available data shows lack of lipogenesis to have evolved independently at least twice, in parasitic Hymenoptera and Diptera. The underlying genetic mechanism, however, remains to be solved. Furthermore, due to the inability to replenish adult fat reserves, parasitoids are severely constrained in resource allocation strategies, in particular the trade-off between survival and reproduction.     

Susceptibility of the taro beetle, Papuana uninodis (Coleoptera, Scarabaeidae) to two new Bacillus popilliae isolates from Papuana spp

Two morphological types of Bacillus popilliae, causal agent of the milky disease, have been isolated from taro beetles (Papuana spp, Coleoptera: Scarabaeidae). B. popilliae from P. woodlarkiana woodlarkiana (Papua New Guinea) was a type A1 with a small sporangium (4.1 x 1.6 microm) and a large spore (2.1 x 1.4 microm) and parasporal body (1.8 x 1.2 microm) that sometimes overlap. B. popilliae from P. uninodis and P. woodlarkiana laevipennis (Solomon Islands) was a type B2 with a small sporangium (2.8 x 1.3 microm), a small eccentric spore (1.1 x 0.7 microm), and no parasporal body. The infectivity of these B. popilliae to Papuana uninodis larvae was compared with two B. popilliae samples from Popillia japonica in injection tests. The hemolymph of P. uninodis supported the germination and growth of isolates from Papuana and P. japonica. Results were similar in third instars and adults. Highest infection (spores present) and mortality was caused by the isolates from Papuana: mortality reached almost 100% 4 weeks after injection of the B2 type B. popilliae with 40% of larvae and 52% of adults infected. Injection of type A1 caused lower mortality but a similar percentage infected. Of two A1 B. popilliae from P. japonica, one caused a mortality comparable to type A1 from Papuana but lower infection; an older isolate resulted in low mortality and only one infected larva. B. popilliae type A1 from P. woodlarkiana was produced in the Solomon Islands by injection of spores in P. uninodis. Thirty four percent of the injected larvae and 31% of the adults produced spores with an average yield of 3.2 and 0.8 x 10(9) spores/insect, respectively. Oral application of a single dose of 10(7) spores of the B. popilliae isolates from P. uninodis or P. japonica did not cause infection and similarly inoculation of the food with spores of B. popilliae type B2 did not result in infections. However, when different rates were applied to the food of second- and third-instar P. uninodis, the B. popilliae type A1 from P. woodlarkiana caused up to 15% infection and concentration-related mortality.     

Contrasting rates of mitochondrial molecular evolution in parasitic Diptera and Hymenoptera

We investigated the putative association between the parasitic lifestyle and an accelerated rate of mt genetic divergence, compositional bias, and gene rearrangement, employing a range of parasitic and nonparasitic Diptera and Hymenoptera. Sequences were obtained for the cox1, cox2, 16S, 28S genes, the regions between the cox2 and atp8 genes, and between the nad3 and nad5 genes. Relative rate tests indicated generally that the parasitic lifestyle was not associated with an increased rate of genetic divergence in the Diptera but reaffirmed that it was in the Hymenoptera. Similarly, a departure from compositional stationarity was not associated with parasitic Diptera but was in parasitic Hymenoptera. Finally, mitochondrial (mt) gene rearrangements were not observed in any of the dipteran species examined. The results indicate that these genetic phenomena are not accelerated in parasitic Diptera compared with nonparasitic Diptera. A possible explanation for the differences in the rate of mt molecular evolution in parasitic Diptera and Hymenoptera is the extraordinary level of radiation that has occurred within the parasitic Hymenoptera but not in any of the dipteran parasitic lineages. If speciation events in the parasitic Hymenoptera are associated with founder events, a faster rate of molecular evolution is expected. Alternatively, biological differences between endoparasitic Hymenoptera and endoparasitic Diptera may also account for the differences observed in molecular evolution.     

Survey of the native insect natural enemies of Hyphantria cunea (Drury) (Lepidoptera: Arctiidae) in China

The fall webworm, Hyphantria cunea (Drury) (Lepidoptera: Arctiidae), is an invasive and important pest in China. Investigations on insect natural enemies have been conducted from 1996 to 1999 in five provinces and one municipality of China in order to select effective species for biological control. Two carabid predators (Coleoptera) and 25 parasitoid species were found, among which 23 were parasitic wasps (Hymenoptera), including five hyperparasitic species and two tachinid flies (Diptera). The two carabids preyed on young larvae inside webs, two braconid wasps parasitized larvae, and 18 parasitoid species attacked the fall webworm during the pupal and/or 'larval-pupal' stages. Among these parasitoids, there were one genus and nine species that are new to science and four species new to China, which were described and published by the senior author Yang. The average parasitism rates of fall webworm pupae were 25.8% and 16.1% in the overwintering generation and the first generation (summer generation), respectively. These findings reveal that these natural enemies play an important role in the natural control of the pest. Chouioia cunea Yang (Hymenoptera: Eulophidae), a gregarious pupal endo-parasitoid, was recommended as a promising biological control agent against the fall webworm in China.     

A fly larva (Syrphidae: Ocyptamus) that preys on adult flies

Predatory syrphid larvae feed on relatively immobile prey, but here we report the first case (as far as we are aware) of obligatory predation on very mobile prey. Larvae of an undescribed species of Ocyptamus (Diptera: Syrphidae) were found in whitefly (Hemiptera: Aleyrodidae) aggregations on the undersides of citrus leaves. However, instead of preying on the whitefly nymphs (as would be expected), the larvae preyed on adult flies (Diptera) that were attracted to the honeydew. In the laboratory, larvae captured significantly more flies on whitefly infested leaves than on washed leaves, and generally abandoned leaves that lacked whiteflies. Most cases of successful prey capture involved flies that probed the anterior part of the larva's body with its proboscis (as if it were honeydew). The syrphid larva lashed out at the fly and entangled it in sticky oral secretion. The prey did not recover when they were removed from the larva, suggesting that this new predatory species also employs venom to subdue its prey. Although the larvae consumed some honeydew, they were unable to complete their development on this diet. Two parasitoids were reared from Ocyptamus puparia, Proaspicera sp. (Hymenoptera: Figitidae) and Paracarotomus sp. (Hymenoptera: Pteromalidae), both of which are endoparasitic koinobionts.     

Paenibacillus associated with milky disease in Central and South American scarabs

Thirty-one isolates of bacteria causing milky disease in scarab larvae collected in Central and South America were identified as Paenibacillus popilliae or Paenibacillus lentimorbus by use of DNA similarity analysis. The isolates were more similar to each other than to the North American isolates that are the type strains of the species. All of the bacteria of both species produced parasporal bodies, a characteristic previously believed to be unique to P. popilliae. Screening of the bacteria using PCR with parasporal protein primers revealed differences among the parasporal protein genes of P. popilliae isolates and between the parasporal genes of P. popilliae and P. lentimorbus. In contrast to P. popilliae from North America, none of the isolates from Central and South America was resistant to vancomycin, an indication of an interesting geographic distribution of the resistance genes.     

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.     

Endoparasitoids of larval Anomis privata (Lepidoptera: Noctuidae), major pest of Hibiscus syriacus (Columniferae: Malvaceae)

Endoparasitoids of Anomis privata larvae include five species in three families of two orders. In this work, two species of Hymenoptera Braconidae (Cotesia sp., Microplitis sp.), one species of Ichneumonidae (Mesochorus vittator) and two species of Diptera Tachinidae (Exorista (Podotachina) sorbillans, Timavia amoena) were investigated. Of the 261 larvae of A. privata examined, 32 had a parasite, so the rate of parasitism was 12.26%. Parasitism by taxon was the highest, at 10.35% (27 individuals), in Cotesia sp. in Hymenoptera Braconidae. Parasitoids of Braconidae and Ichneumonidae were larval parasitoids. A parasitic insect of Tachinidae was a larva–pupal parasitoid. Solitary parasitoids included Microplitis sp. in Braconidae and E. sorbillans in Tachinidae. Gregarious parasitoids included Cotesia sp. in Braconidae, M. vittator in Ichneumonidae and T. amoena in Tachinidae. There was also a multiparasitoid (T. amoena) and two superparasitoids (Cotesia sp., M. vittator). A larva of A. privata sought feed even after it was parasitized every parasitoid investigated in this study, so five species of parasitoids were all koinobiont.     

Systemic Imidacloprid Affects Intraguild Parasitoids Differently

Toxoneuron nigriceps (Viereck) (Hymenoptera, Braconidae) and Campoletis sonorensis (Cameron) (Hymenoptera, Ichneumonidae) are solitary endoparasitoids of the tobacco budworm, Heliothis virescens (Fabricius) (Lepidoptera, Noctuidae). They provide biological control of H. virescens populations in Southeastern US agricultural production systems. Field and greenhouse experiments conducted from 2011–2014 compared parasitism rates of parasitoids that developed inside H. virescens larvae fed on tobacco plants treated with and without imidacloprid. The parasitoids in our study did not have a similar response. Toxoneuron nigriceps had reduced parasitism rates, but parasitism rates of C. sonorensis were unaffected. Preliminary data indicate that adult female lifespans of T. nigriceps are also reduced. ELISA was used to measure concentrations of neonicotinoids, imidacloprid and imidacloprid metabolites in H. virescens larvae that fed on imidacloprid-treated plants and in the parasitoids that fed on these larvae. Concentrations were detectable in the whole bodies of parasitized H. virescens larvae, T. nigriceps larvae and T. nigriceps adults, but not in C. sonorensis larvae and adults. These findings suggest that there are effects of imidacloprid on multiple trophic levels, and that insecticide use may differentially affect natural enemies with similar feeding niches.     

Rearing of the fruit fly parasitoid Diachasmimorpha longicaudata (Hymenoptera: Braconidae) on X-ray irradiated larvae of Ceratitis capitata (Diptera: Tephritidae)

We evaluated the effects of X-ray irradiation on larvae of Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), with the aim of finding a treatment that prevented adult fly emergence, yet did not adversely affect larval quality as rearing hosts for the parasitoid Diachasmimorpha longicaudata (Ashmead) (Hymenoptera: Ichneumonidae). Two experiments were carried out. In the first experiment, small numbers of larvae were held in Petri dishes with and without small amounts of rearing media and then irradiated with doses of X-rays ranging from 0 to 8333.6 R (equivalent to 80 Gy). In the second experiment, higher numbers of larvae were held in a manner resembling mass-rearing conditions, and were then irradiated with X-rays ranging from 0 to 10,417 R (equivalent to 100 Gy). In both experiments, the only factor that significantly affected fly emergence was irradiation of larvae. Fly emergence decreased markedly as the irradiation dose increased, and complete suppression of fly emergence was achieved at 6250.2 R (equivalent to 60 Gy) when larvae were irradiated in small batches with or without rearing media. Irradiation also affected the fertility of those flies that did emerge following treatment. In the second experiment, we found the parasitoids reared from irradiated larvae produced a higher parasitism rate and a higher number of female offspring than did parasitoids reared from control (non-irradiated) larvae. Mean fecundity of F1 parasitoids reared from irradiated larvae were affected positively by irradiation only at the 8333.6 R (80 Gy) dose. Our results show that X-ray irradiation can be used to inhibit fruit fly adult emergence and that irradiated larvae are at least as good a rearing substrate as non-irradiated larvae. Future studies should focus on the adjustment of our findings to a mass-rearing scale.     

The spatio-temporal distribution dynamics of the cabbage seedpod weevil, Ceutorhynchus obstrictus (Coleoptera: Curculionidae), and its larval parasitoids in canola in western Canada

Distribution patterns of the cabbage seedpod weevil, Ceutorhynchus obstrictus (Marsham) (Coleoptera: Curculionidae), and its larval parasitoids were investigated in commercial fields of spring canola (Brassica rapa L. and Brassica napus L.) in southern Alberta, Canada, from 2002 to 2004 in relation to developmental stages of its host plants. Adult weevils invaded fields along one or more fronts when crops were in bud to early flower. Significant clustering of adults along field edges in early stages of invasion was followed by more homogeneous distributions as canola reached the mid to late flowering and pod enlargement stages. Larval weevil distributions, as indicated by exit holes in siliques at the end of the season, were often aligned spatially with adult distributions, but they did not coincide in all regions of the fields. The primary ectoparasitoid species attacking weevil larvae comprised Necremnus tidius (Walker) (Hymenoptera: Eulophidae), and Trichomalus lucidus (Walker), Chlorocytus sp., and Pteromalus sp. (Hymenoptera: Pteromalidae). Parasitism rates increased from 0.1 to 5.0% over the three years of study. Parasitoid distributions were often, but not consistently, spatially associated with high densities of C. obstrictus larvae. Lack of close spatial alignment of parasitoids and their hosts probably reflects low parasitoid numbers in comparison with an abundant resource of weevil larvae, and a lack of co-evolutionary history between host and parasitoids. Some parasitoids invaded fields early in host plant development, at the same time that weevils invaded. Unfortunately the synchronous invasions of host and parasitoids indicate that insecticidal applications to reduce adult weevil infestations may be detrimental to these beneficial species.     

The parasitoid guild of larvae of Chrysophtharta agricola Chapuis (Coleoptera: Chrysomelidae) in Tasmania, with notes on biology and a description of a new genus and species of tachinid fly

Abstract  The taxonomic status of the parasitoid guild associated with the larvae of Southern Eucalypt Beetle ( Chrysophtharta agricola Chapuis) in Tasmania is discussed. The primary larval parasitoid complex comprised the tachinid flies Balde striatum gen. n., sp. n. and Paropsivora australis (Macquart) (Diptera: Tachinidae: Goniinae: Blondeliini), and Eadya paropsidis Huddleston & Short (Hymenoptera: Braconidae), while the hymenopteran hyperparasitoids included Perilampus tasmanicus (Cameron) (Perilampidae), Mesochorus sp. (Ichneumonidae) and possibly Meteorus sp. (Braconidae). Keys are provided to the three adult primary parasitoids and two adult hyperparasitoids, and to the pupae of primary parasitoids. Balde striatum gen. n., sp. n. is described, and P. australis is redescribed. Brief notes on biology are included.     

Association of Ovavesicula popilliae (Microsporida: Ovavesiculidae) with winter mortality of larvae and reduced fecundity of female Japanese beetles (Coleoptera: Scarabaeidae)

Populations of Japanese beetle at sites in Michigan where Ovavesicula popilliae (Andreadis) was introduced in 1999 and 2000 were compared with nearby control sites from fall of 2005 through spring of 2008. Percent infection by O. popilliae and winter mortality of Japanese beetle were determined by sampling larvae in October and April from 12 golf holes on six courses in southeast Michigan and eight holes on four courses in southwest Michigan. Adult Japanese beetles were also collected from these golf courses in July and August of 2007 to determine the impact of O. popilliae-infection on egg development in females. In southeast Michigan, O. popilliae appeared to spread rapidly from the 100 m(2) plots where it was previously introduced to surrounding golf course holes between 2000 and 2006. However, data from southwest Michigan suggests that O. popilliae had already been introduced into the area. Regression analysis of data from all 20 golf course holes gives a significant relationship between percent infection of larvae with O. popilliae and winter mortality of Japanese beetle. Mean winter mortality of larvae around golf course holes where <10% were infected with O. popilliae was 24.7% compared with 41.7% mortality where 10-30% were infected, and 72.0% mortality where >30% were infected. Females infected with O. popilliae contained 50% fewer mature eggs than uninfected females. In addition, females from golf courses where all of the fairways and roughs were treated annually with imidacloprid contained 48% fewer mature eggs than females from golf courses where insecticides were only used on the fairways or not at all.     

Variation in diapause and sex ratio in the parasitoidAsobara tabida

Asobara tabida Nees (Hymenoptera: Braconidae) is a widespread parasitoid, attacking larvae ofDrosophila (Diptera: Drosophilidae) species in fermenting substrates. In this species, geographic variation is found in the percentage of parasitoids entering diapause and in the sex ratio of emerging parasitoids. Percentage diapause appears to be influenced by host species (more parasitoids enter diapause inD. melanogaster Meigen than inD. subobscura Collin) and temperature. It is not correlated with any of the abiotic factors investigated, but is correlated with survival probability inD. melanogaster larvae and with the time of year in which the experiment was conducted (even though none of the parasitoids experienced natural day light). Sex ratio was only found to correlate with percentage diapause, suggesting that males enter diapause more frequently than females. It is concluded thatA. tabida uses diapause to survive both unfavourable abiotic and biotic circumstances.     

闭弯尾姬蜂与菜蛾盘绒茧蜂寄生菜蛾幼虫时的种间竞争

在室内25℃下,以菜蛾3龄初幼虫作寄主,研究了菜蛾盘绒茧蜂Cotesia plutellae和半闭弯尾姬蜂Diadegma semiclausum的种间竞争。当寄主供2种蜂同时产卵寄生时,2种蜂各自的寄生率与其单独寄生时无显著差异,合计寄生率比一种蜂单独存在时有所提高,但差异不显著。2种蜂均能产卵寄生已被另一种蜂寄生了的寄主幼虫。当寄主被2种蜂寄生的间隔时间很短（少于10 h）时,所育出的蜂绝大部分（80%以上）为绒茧蜂;当寄主先被绒茧蜂寄生,并饲养2天以上再供弯尾姬蜂寄生时,所育出的全为绒茧蜂;当寄主先被弯尾姬蜂寄生,并饲养2天以上再供绒茧蜂寄生时,寄主幼虫绝大部分不能存活,只有少部分能育出寄生蜂,且多为弯尾姬蜂。当2种蜂的幼虫存在于同一寄主体内时,2种蜂的发育均受到另一种蜂的抑制;绒茧蜂1龄幼虫具有物理攻击能力,能将弯尾姬蜂卵或幼虫致死。这些结果表明,菜蛾盘绒茧蜂与半闭弯尾姬蜂在同一寄主中发育时,前者具有明显的竞争优势。     

Two new species of Torymus Dalman, 1820 (Hymenoptera: Torymidae) parasitizing Celticecis japonica Yukawa and Tsuda, 1987 (Diptera: Cecidomyiidae) that induce leaf galls on Celtis species (Ulmaceae) in Japan

Torymus celticolus Matsuo sp. nov. and Torymus celtidigalla Matsuo sp. nov. (Hymenoptera: Torymidae) are described as parasitoids of larvae of Celticecis japonica Yukawa & Tsuda, 1987 (Diptera: Cecidomyiidae) that induce leaf galls on Celtis species (Ulmaceae) in Japan. A key to species of the genus Torymus known in Japan is provided.     

Intraguild predation of the aphid parasitoid Aphelinus certus by Coccinella septempunctata and Harmonia axyridis

Coincidental intraguild predation is expected to be less disruptive to biological control than omnivorous intraguild predation, and strong intraguild predation is not expected to occur in natural systems. Coincidental intraguild predation in a foodweb involving introduced pest and natural enemy species was examined to determine whether intraguild predation would be disruptive of biological control services in soybean agroecosystems. Introduced natural enemies are important regulators of soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), populations in North America. Seven-spotted lady beetles, Coccinella septempunctata L., and multicolored Asian lady beetles, Harmonia axyridis Pallas (Coleoptera: Coccinellidae), are key predators of soybean aphid in North America while the chalcidoid wasp, Aphelinus certus Yasnosh (Hymenoptera: Aphelinidae), is the most common parasitoid of soybean aphid in Ontario, Canada. Predation of parasitized soybean aphids at two stages (newly parasitized aphids and mummified aphids) by adults and third instar larvae of both C. septempunctata and H. axyridis was examined in laboratory experiments. In choice experiments, all stages of lady beetles preferred non-parasitized aphids over mummified aphids. In cage experiments, third instar larvae and male and female adults of both lady beetles did not discriminate between newly parasitized and non-parasitized aphids. The influence of coincidental intraguild predation on the efficacy of parasitoids as biological control agents, and implications for soybean aphid management decisions based on natural enemies, are discussed.     

Larval development of two parasitic flies (Conopidae) in the common host Bombus pascuorum

Abstract.

• 1 Whenever parasitism by more than one female occurs, larvae of parasitoids not only have to resist host defence but also face competition with other (unrelated) larvae. Competition is particularly important in solitary parasitoids where only one larva is able to complete its development. Such a situation is found in Conopidae (Diptera) parasitizing adult bumble bees where larvae of two species of conopid flies, Sicus ferrugineus L. and Physocephala rufipes F. often compete within the common host Bombus pascuorum Scopoli. This study analysed the larval development of the two species and asks how competition among larvae may be regulated.
• 2 Parasitized workers of B.pascuorum were caught in the field and kept according to different experimental schedules in the laboratory. This provided stage-structured data for the temporal course of development of the parasitic larvae. For the analysis, a simulation model was constructed that estimated the duration of all parasitic stages (Manly, 1990, first method). In both species the egg stage was found to be approximately 2 days, first instar 3 days, second instar 4 days, and third instar 3 days. The total development time is an estimated 10.8 days from oviposition in S.ferrugineus and 11.4 days in P.rufipes. S.ferrugineus develops faster in the beginning, probably because of its larger egg size, whereas P.rufipes pupates at larger size. First-instar larvae of both species possess strong, pointed mandibles.
• 3 The success of conopid larvae seems only marginally affected by host defence, for a single larva per host almost always completes development. Under competition, however, mortality rate increases substantially, and most larvae die in their first instar. Moreover, they show signs of melanization. The estimates for developmental times and the patterns found in this study suggest that conopid larvae seem capable of physical attacks, particularly during the first instar, when elimination of competitors is most common, and that S.ferrugineus has a time advantage because of its faster early development. Because most studies have previously been carried out with hymenopteran parasitoids, this study provides new information about the other large group of parasitoid insects, the Diptera, and demonstrates convergent patterns.