Diachasma Alloeum Research Articles

Cold tolerance and diapause within and across trophic levels: Endoparasitic wasps and their fly host have similar phenotypes

Low temperatures associated with winter can limit the survival of organisms, especially ectotherms whose body temperature is similar to their environment. However, there is a gap in understanding how overwintering may vary among groups of species that interact closely, such as multiple parasitoid species that attack the same host insect. Here, we investigate cold tolerance and diapause phenotypes in three endoparasitoid wasps of the apple maggot fly Rhagoletis pomonella (Diptera: Tephritidae): Utetes canaliculatus, Diachasma alloeum, and Diachasmimorpha mellea (Hymenoptera: Braconidae). Using a combination of respirometry and eclosion tracking, we found that all three wasp species exhibited the same three diapause duration phenotypes as the fly host. Weak (short duration) diapause was rare, with <5 % of all three wasp species prematurely terminating diapause at 21 °C. Most D.mellea (93 %) entered a more intense (longer duration) diapause that did not terminate within 100 d at this warm temperature. The majority of U.canaliculatus (92 %) and D. alloeum (72 %) averted diapause (non-diapause) at 21 °C. There was limited interspecific variation in acute cold tolerance among the three wasp species: wasps and flies had similarly high survival (>87 %) following exposure to extreme low temperatures (−20 °C) as long as their body fluids did not freeze. The three wasp species also displayed little interspecific variation in survival following prolonged exposure to mild chilling of 8 or more weeks at 4 °C. Our study thus documents a remarkable conservation of cold tolerance and diapause phenotypes within and across trophic levels.

Olfactory Sensilla and Olfactory Genes in the Parasitoid Wasp Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae).

Simple SummaryParasitic wasps are the major natural enemies of many organisms, and therefore they are broadly used in the biological control of numerous agricultural and horticultural pests. For example, Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae) is a tiny natural egg parasitoid of various agricultural pest insects, including Plutella xylostella, Helicoverpa armigera, Spodoptera frugiperda and Ectomyelois ceratoniae. However, how T. pretiosum seek and localise host insect eggs is still not clear. The olfactory system is critical in guiding insect behaviours, including mating, feeding and oviposition, which play pivotal roles in the interactions between parasitoid wasps and their hosts. This project aimed to investigate T. pretiosum major olfactory tissue (antennae) and the olfactory genes, including odorant binding proteins (OBPs) and odorant receptors (ORs). T. pretiosum adult antennae were examined under scanning electron microscopy, and four types of olfactory sensilla were observed. Using T. pretiosum genome, 22 OBPs and 105 ORs were identified, which were further compared with olfactory genes of other Hymenoptera insect species. The expression patterns of OBPs between T. pretiosum male and female adults were examined to identify female- or male-specific OBPs. This study enriches our knowledge of T. pretiosum olfactory system and will help better use it in the integrated pest management (IPM) for many insect pest species.Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae) is a tiny natural egg parasitoid of several agricultural pest insects, which has been widely used in the biological control for Plutella xylostella, Helicoverpa armigera, Spodoptera frugiperda and Ectomyelois ceratoniae. However, limited studies have been conducted on T. pretiosum olfactory system, which is critical in regulating insect behaviours. In this study, T. pretiosum adult antennae were investigated under ascanning electron microscopy (SEM). Four types of olfactory sensilla were observed, including chaetica sensilla (CS), trichoid sensilla (TS), faleate sensilla (FS) and placoid sensilla (PS). Using T. pretiosum genome, 22 putative odorant binding proteins (OBPs) and 105 odorant receptors (ORs) were identified, which were further compared with olfactory genes of Apis mellifera, Nasonia vitripennis and Diachasma alloeum. The expression patterns of OBPs between T. pretiosum male and female adults were examined by quantitative real time PCR (qRT-PCR) approaches. Three female-specific OBPs (TpreOBP19, TpreOBP15 and TpreOBP3) were identified, which may play crucial roles in T. pretiosum host-seeking and oviposition behaviours. This study enriches our knowledge of T. pretiosum olfactory genes and improves our understanding of its olfactory system.

Bracon brevicornis Genome Showcases the Potential of Linked-Read Sequencing in Identifying a Putative Complementary Sex Determiner Gene.

Bracon brevicornis is an ectoparasitoid of a wide range of larval-stage Lepidopterans, including several pests of important crops, such as the corn borer, Ostrinia nubilalis. It is also one of the earliest documented cases of complementary sex determination in Hymenoptera. Here, we present the linked-read-based genome of B. brevicornis, complete with an ab initio-derived annotation and protein comparisons with fellow braconids, Fopius arisanus and Diachasma alloeum. We demonstrate the potential of linked-read assemblies in exploring regions of heterozygosity and search for structural and homology-derived evidence of the complementary sex determiner gene (csd).

Identification of Neuropeptides and Their Receptors in the Ectoparasitoid, Habrobracon hebetor.

Neuropeptides are a group of signal molecules that regulate many physiological and behavioral processes by binding to corresponding receptors, most of which are G-protein-coupled receptors (GPCRs). Using bioinformatic methods, we screened genomic and transcriptomic data of the ectoparasitoid wasp, Habrobracon hebetor, and annotated 34 neuropeptide candidate precursor genes and 44 neuropeptide receptor candidate genes. The candidate neuropeptide genes were found to encode all known insect neuropeptides except allatotropin, neuropeptide F, pigment dispersing factor, and CCHamides. When compared with the endoparasitic wasp Pteromalus puparum and the ectoparasitic wasp Nasonia vitripennis, trissin and FMRFamide were found only in H. hebetor. A similar result held for the neuropeptide receptor genes, for the receptors were found in H. hebetor except the receptors of CCHamides and neuroparsin. Furthermore, we compared and analyzed the differences in neuropeptides in eight Braconidae wasps and identified natalisin in H. hebetor, Diachasma alloeum, Fopius arisanus and Microplitis demolitor, but not in the other wasps. We also analyzed the transcriptome data and qRT-PCR data from different developmental stages and tissues to reveal the expression patterns of the neuropeptides and their receptors. In this study, we revealed composition of neuropeptides and neuropeptide receptors in H. hebetor, which may contribute to future neurobiological studies.

Genome of the Parasitoid Wasp Diachasma alloeum, an Emerging Model for Ecological Speciation and Transitions to Asexual Reproduction.

Parasitoid wasps are among the most speciose animals, yet have relatively few available genomic resources. We report a draft genome assembly of the wasp Diachasma alloeum (Hymenoptera: Braconidae), a host-specific parasitoid of the apple maggot fly Rhagoletis pomonella (Diptera: Tephritidae), and a developing model for understanding how ecological speciation can “cascade” across trophic levels. Identification of gene content confirmed the overall quality of the draft genome, and we manually annotated ∼400 genes as part of this study, including those involved in oxidative phosphorylation, chemosensation, and reproduction. Through comparisons to model hymenopterans such as the European honeybee Apis mellifera and parasitoid wasp Nasonia vitripennis, as well as a more closely related braconid parasitoid Microplitis demolitor, we identified a proliferation of transposable elements in the genome, an expansion of chemosensory genes in parasitoid wasps, and the maintenance of several key genes with known roles in sexual reproduction and sex determination. The D. alloeum genome will provide a valuable resource for comparative genomics studies in Hymenoptera as well as specific investigations into the genomic changes associated with ecological speciation and transitions to asexuality.

De novo sequencing and transcriptome analysis of female venom glands of ectoparasitoid Bracon hebetor (Say.) (Hymenoptera: Braconidae)

Venom is a key-factor in the regulation of host physiology by parasitic Hymenoptera and a potentially rich source of novel bioactive substances for biotechnological applications. The limited study of venom from the ectoparasitoid Bracon hebetor, a tiny wasp that attacks larval pest insects of field and stored products and is thus a potential insect control agent, has not described the full complement and composition of these biomolecules. To have a comprehensive picture of genes expressed in the venom glands of B. hebetor, a venom gland transcriptome was assembled by using next generation sequencing technologies followed by de novo assemblies of the 10.81 M sequence reads yielded 22,425 contigs, of which 10,581 had significant BLASTx hits to know genes. The majority of hits were to Diachasma alloeum, an ectoparasitoid from same taxonomic family, as well as other wasps. Gene ontology grouped the sequences into molecular functions in which catalytic activity with 42.2% was maximum, cellular components in which cells with 33.8% and biological processes among which metabolic process with 30% had the most representatives. In this study, we highlight the most abundant sequences, and those that are likely to be functional components of the venom for parasitization. Full length ORFs of Calreticulin, Venom Acid Phosphatase Acph-1 like protein and arginine kinase proteins were isolated and their tissue specific expression was studied by RT-PCR. Our report is the first to characterize components of the B. hebetor venom glands that may be useful for developing control tools for insect pests and other applications.

Meek mothers with powerful daughters: effects of novel host environments and small trait differences on parasitoid competition

Outcomes of competition may depend both on subtle differences in traits relevant to fitness and on how those traits are expressed in the context of the environment. Environmental effects on traits impacting population dynamics are often overlooked in studies of parasitic wasp (parasitoid) competition. Lineages of the parasitoid Diachasma alloeum (Hymenoptera: Braconidae) differ in relative ovipositor length (a trait affecting the proportion of hosts available for parasitism). Since the size of natal hosts affects the overall body size of many adult parasitoids, outcomes of competition between D. alloeum lineages should be influenced by both their natal host's size and their inherited ovipositor:body size ratios. Previous genetic work showed the unexpected result that the apparently inferior competitor (the lineage with smaller ovipositors in its ancestral environment) has successfully colonized a new host. We present body size measurements and a phenomological model of competition showing that relative ovipositor sizes of the two lineages predict success of the apparently inferior wasp lineage in the new host. We present several variants of the model, including simulations: 1) wherein competitors have either ancestral trait values or trait values acquired in the novel environment; 2) that allow varying rates of constant immigration from the inferior competitor's source population; and 3) with stochastic immigration from both lineages' source populations. We show that ancestral trait differences and changes in environmentally mediated traits interact to affect outcomes of competition. Apparently inferior female parasitoids (‘meek mothers’) attacking a host in a novel environment can produce highly successful daughters if those daughters inherit large ovipositor:body size ratios and grow to a larger size in the new environment. Predictive models of parasitoid competition that consider effects of environmentally mediated trait changes may be particularly important for biocontrol programs wherein parasitoids are introduced into new environments or used to control novel hosts.

Geographic and Ecological Overlap of Parasitoid Wasps Associated with the Rhagoletis pomonella (Diptera: Tephritidae) Species Complex

Abstract One of the fundamental questions in evolutionary ecology seeks to understand how new biodiversity is created and structured into communities. The apple maggot, Rhagoletis pomonella (Walsh) (Diptera: Tephritidae), a model for rapid ecological speciation via host plant shifting for phytophagous insects, and its parasitoid community can offer insight into answering this and other related questions. Speciation of Rhagoletis also seems to be driving sequential speciation in a host specific parasitoid wasp Diachasma alloeum (Muesebeck) (Hymenoptera: Braconidae). However, biological and geographic information regarding D. alloeum and other parasitoids attacking flies in the genus Rhagoletis is sorely lacking, a problem that complicates the study of their evolution. Here, we present a synthesis of the geographic ranges and extended host associations of Rhagoletis-attacking parasitoids and test whether parasitoids can overlap in host use. In particular, we ask whether 1) wasps that co-occur in sympatry attack different life stages of the fly, 2) locally co-occurring wasps share some fly species in common but not others, 3) wasps differ in local abundance on those fly hosts they share in common, and 4) wasps vary on a regional scale in their geographic distributions. We use both collections and published records to answer the above-mentioned questions. A strong understanding of the Rhagoletis-attacking parasitoid distributions will facilitate future study of sequential radiation in this system.

Oviposition Marking Behavior of Diachasma alloeum, (Hymenoptera: Braconidae), Parasitizing Rhagoletis pomonella, (Diptera: Tephritidae)

Diachasma alloeum (Muesebeck) (Hymenoptera: Braconidae) is a solitary larval endoparasitoid attacking Rhagoletis (Diptera: Tephritidae) species. Rhagoletis pomonella (Walsh) mark the surface of fruit after oviposition with an oviposition marking pheromone (OMP) which deters conspecific female flies. Herein we demonstrate that female D. alloeum wasps reared from either apple or hawthorn race R. pomenella larvae also deposit an OMP that reduces oviposition by conspecific female wasps. Significantly fewer wasps accepted fruit that had received prior wasp oviposition and OMP or OMP alone without oviposition compared with control fruit for a minimum of 7 days on both fruit types. Rinsing fruit with a 50% ethanol solution appeared to remove the OMP rendering fruit more acceptable for oviposition than marked fruit that was not rinsed. Wasps of each host race were able to detect and avoid the OMP of the sister race and fruit substrate type did not affect wasp response to the pheromone. The possibility of an internal marker deposited during oviposition is also discussed.

Transfer of life-history phenology from mothers to progeny in a solitary univoltine parasitoid

Among univoltine insects that experience diapause, differences in emergence timing between adult males and females are expected to be dictated by sex-specific developmental factors. In multivoltine insects without a diapause, there is often an additional relationship between the date of oviposition and the date of adult emergence. Differences between male and female emergence timing in the latter case can therefore be influenced by female sex-allocation decisions. In the present study, it is shown that eggs of a univoltine parasitoid wasp Diachasma alloeum Muesebeck (Hymenoptera: Braconidae) that are laid earlier also eclose earlier during the subsequent year, independent of (although complementary to) sex-related differences in development time. The implications of this pattern for sex allocation decisions by female univoltine parasitoids are discussed.

Sequential speciation and the diversity of parasitic insects

A major issue in biology is what generates biodiversity. An important part of the answer may be biodiversity itself. As new species form they may often create new niches, providing an impetus for other organisms to adapt and speciate. This hypothesis of ‘cascading’ or ‘sequential’ speciation has been argued to be particularly relevant for host‐plant‐specific phytophagous insects and their associated parasites. Here, we discuss the empirical and theoretical bases for sequential speciation and its potential significance for understanding the genesis of new life forms. We examine the application of the concept that biodiversity begets biodiversity by palaeontologists, ecologists, and evolutionary biologists to explain current and past distributions of organisms. We look at factors that may promote and restrict sequential speciation and review evidence from phytophagous insects for the process in nature. In particular, we discuss a case study involving the apple maggot fly, Rhagoletis pomonella (Diptera: Tephritidae) and its wasp parasitoid Diachasma alloeum (Hymenoptera: Braconidae). We conclude by outlining a research agenda for testing for sequential speciation in the field.

Recognition of foreign oviposition-marking pheromone in a multi-trophic context

Both phytophagous and parasitic insects deposit oviposition-marking pheromones (OMPs) following oviposition that function to inform conspecifics of a previously utilized host of reduced suitability. The blueberry maggot fly, Rhagoletis mendax Curran (Diptera: Tephritidae), deposits eggs individually into blueberries and then marks the fruit surface with an OMP which reduces acceptance of fruit for oviposition by conspecifics. Diachasma alloeum (Muesebeck) (Hymenoptera: Braconidae) is a parasitic wasp attacking larval R. mendax which also deposits an OMP, signaling conspecifics of a wasp-occupied host. Behavioral studies were conducted testing the hypothesis that the OMP of the parasitic wasp modifies the oviposition behavior of its host fly. In this study, we show that the OMP of D. alloeum is recognized by R. mendax, and female flies will reject wasp-marked fruit for oviposition. Thus, we present a rare demonstration of pheromonal recognition between animals occupying different taxonomic orders and trophic levels. This chemical eavesdropping may enhance the ability of the fly to avoid fruit unsuitable for larval development.

PERMANENT GENETIC RESOURCES: Polymorphic microsatellite loci for Diachasma alloeum (Hymenoptera: Braconidae)

Here, we report the isolation of 21 novel primers for amplification of microsatellite loci in Diachasma alloeum (Hymenoptera: Braconidae). Diachasma alloeum is a larval parasitoid of the apple maggot fly (Rhagoletis pomonella), which is an economically significant agricultural pest species and a textbook example of sympatric speciation via host-plant shifting. These microsatellite markers will prove useful both for assessing genetic relationships between different host-associated populations of D. alloeum, as well as for future R. pomonella biological control programmes. We also report the cross-species amplification of several loci for Diachasmimorpha mellea and Diachasma ferrugineum, parasitoids of R. pomonella and R. cingulata, respectively.

Oviposition-deterring pheromone deposited on blueberry fruit by the parasitic wasp, Diachasma alloeum

Insect parasitoids are known to deposit chemical signals on utilized hosts following oviposition. It is believed that these chemical signals alert future conspecifics of an exploited and thus sub-optimal host alleviating potential suffering among brood that would otherwise compete over a limited resource. Diachasma alloeum (Muesebeck) is a braconid wasp that specifically attacks two species of fruit-parasitic flies in the genus Rhagoletis . Female wasps lay a single egg into a second or third instar fly maggot developing in blueberry, hawthorn, or apple fruit. Following oviposition, female wasps press and drag their ovipositor across the fruit surface depositing a clear liquid; this has been termed 'excreting' behaviour. In this report, we describe excreting behaviour in a field population of D. alloeum attacking the blueberry maggot fly, Rhagoletis mendax Curran. Subsequently, we demonstrate in a series of laboratory assays that D. alloeum females deposit a substance on blueberry fruit directly following egg laying that deters subsequent naïve females from ovipositing into the marked fruit. Marking fruit with this putative oviposition-deterring pheromone without associated egg laying was sufficient to induce the deterring effect, while oviposition alone without subsequent marking had no effect. The oviposition-deterring effect was removed by rinsing fruit with a solution of 50% ethanol in water. Spraying unmarked fruit with an ethanol-water rinsate of previously-marked berries induced the oviposition-deterring effect. Significant deterrence of oviposition lasted up to 7 days after marking. To our knowledge, this is the first demonstration of a hymenopteran oviposition-deterring pheromone that is deposited externally on the surface of the fruit skin rather than on the surface of the parasitized larva. Female D. alloeum maximally parasitize second-instar R. mendax larvae during a short 4-5 d window. The length of activity of the oviposition-deterring pheromone described here should be sufficient to prevent multiple egg-laying into a host that cannot support more than one parasitoid larva, and thus reduce intraspecific competition. Insect parasitoids are known to deposit chemical signals on utilized hosts following oviposition. It is believed that these chemical signals alert future conspecifics of an exploited and thus sub-optimal host alleviating potential suffering among brood that would otherwise compete over a limited resource. Diachasma alloeum (Muesebeck) is a braconid wasp that specifically attacks two species of fruit-parasitic flies in the genus Rhagoletis . Female wasps lay a single egg into a second or third instar fly maggot developing in blueberry, hawthorn, or apple fruit. Following oviposition, female wasps press and drag their ovipositor across the fruit surface depositing a clear liquid; this has been termed 'excreting' behaviour. In this report, we describe excreting behaviour in a field population of D. alloeum attacking the blueberry maggot fly, Rhagoletis mendax Curran. Subsequently, we demonstrate in a series of laboratory assays that D. alloeum females deposit a substance on blueberry fruit directly following egg laying that deters subsequent naïve females from ovipositing into the marked fruit. Marking fruit with this putative oviposition-deterring pheromone without associated egg laying was sufficient to induce the deterring effect, while oviposition alone without subsequent marking had no effect. The oviposition-deterring effect was removed by rinsing fruit with a solution of 50% ethanol in water. Spraying unmarked fruit with an ethanol-water rinsate of previously-marked berries induced the oviposition-deterring effect. Significant deterrence of oviposition lasted up to 7 days after marking. To our knowledge, this is the first demonstration of a hymenopteran oviposition-deterring pheromone that is deposited externally on the surface of the fruit skin rather than on the surface of the parasitized larva. Female D. alloeum maximally parasitize second-instar R. mendax larvae during a short 4-5 d window. The length of activity of the oviposition-deterring pheromone described here should be sufficient to prevent multiple egg-laying into a host that cannot support more than one parasitoid larva, and thus reduce intraspecific competition.

Male Diachasma alloeum parasitoids from two host species of tephritid fruit flies respond equally to female-produced sex pheromone

. Diachasma alloeum is a braconid wasp that parasitizes hawthorn-infesting Rhagoletis pomonella and blueberry-infesting Rhagoletis mendax, both tephritid fruit fly sibling species. The behavioural responses of male D. alloeum originating from both fruit fly host species to hexane extracts of conspecific females originating from both host species and females of various mating status are investigated in a laboratory Y-tube olfactometer. Male D. alloeum originating from either R. mendax or R. pomonella respond to one whole-body, female equivalent hexane extract in equal frequency as to a live, virgin female; this response is at least 7.5-fold greater than to solvent controls. Male D. alloeum originating from R. mendax or R. pomonella are attracted to hexane extracts of female D. alloeum abdomens but not to extracts of the head and thorax regions. Virgin D. alloeum females attract significantly more male D. alloeum originating from either host species compared with mated females of the same age. Copulation behaviour between same host and mixed host pairs appears to be identical. Male D. alloeum are equally responsive to the female-produced sex pheromone of female D. alloeum, irrespective of females' host-species origin, suggesting that these host-specific populations can potentially interbreed.

Control strategies for Rhagoletis mendax disrupt host-finding and ovipositional capability of its parasitic wasp, Diachasma alloeum

Diachasma alloeum (Muesebeck) is a braconid parasitoid of Rhagoletis mendax Curran and Rhagoletis pomonella (Walsh). Laboratory choice tests using a Y-tube olfactometer compared behavioral responses of D. alloeum to various olfactory stimuli. More than 25% of naïve D. alloeum females, never having experienced R. mendax or blueberries, were ‘innately’ attracted to volatiles emitted from uninfested blueberry fruit. Experience with R. mendax -infested blueberry fruit approximately doubled the proportion of D. alloeum that subsequently responded to volatiles from uninfested blueberry fruit and decreased the time required to elicit this behavior compared with naïve wasps. Volatiles emanating from infested blueberry fruit, that were oviposited into by R. mendax 16–19 d prior to the assay, attracted four and two times more naïve and experienced D. alloeum , respectively, than uninfested fruit or fruit one day post- R. mendax oviposition. Although parasitoids were found to be attracted to blueberry volatiles in the lab, we hypothesized that insecticide applications targeting R. mendax could interfere with the wasps’ normal host-finding behavior. In field studies, blueberry fruit treated with the neonicotinoid insecticide imidacloprid (Provado 1.6 F) and the kaolin-clay particle film Surround WP, eliminated parasitization of R. mendax by feral D. alloeum . Blueberry fruit treated with the kaolin-clay particle film was equally attractive to D. alloeum as untreated and infested fruit. But, the use of kaolin clay prevented wasps from ovipositing into berries after alighting. The results of this study imply that current management tools for R. mendax may negatively impact the importance of D. alloeum as a biocontrol agent of Rhagoletis flies.

Behavioral evidence for host fidelity among populations of the parasitic wasp, Diachasma alloeum (Muesebeck)

The concept of "host fidelity," where host-specific mating occurs in close proximity to the oviposition site and location of larval development, is thought to impart a pre-mating isolation mechanism for sympatric speciation (sensu members of the genus Rhagoletis). The apple maggot fly, Rhagoletis pomonella, and the blueberry maggot fly, R. mendax, are morphologically similar sibling species thought to have speciated in sympatry by divergence of host plant association. Both of these fly species are attacked by the specialist braconid parasitoid, Diachasma alloeum. The current study demonstrates that both male and female D. alloeum exhibit a behavioral preference for the odor of the fruit of their larval Rhagoletis host species. Specifically, those D. alloeum emerging from puparia of R. pomonella are preferentially attracted to hawthorn fruit and those emerging from puparia of R. mendax are preferentially attracted to blueberry fruit. However, male D. alloeum reared from either R. pomonella or R. mendax were equally attracted to females originating from both Rhagoletis species. We suggest that the data herein present evidence for "host fidelity," where populations of D. alloeum exhibit a greater tendency to mate and reproduce among the host plants of their preferred Rhagoletis hosts. Furthermore, host fidelity may have resulted in the evolution of distinct host races of D. alloeum tracking the speciation of their larval Rhagoletis prey.

FIELD OBSERVATIONS QUANTIFYING ATTRACTION OF THE PARASITIC WASP, DIACHASMA ALLOEUM (HYMENOPTERA: BRACONIDAE) TO BLUEBERRY FRUIT INFESTED BY THE BLUEBERRY MAGGOT FLY, RHAGOLETIS MENDAX (DIPTERA: TEPHRITIDAE)

Abstract The host foraging behavior of the larval parasitoid Diachasma alloeum (Muesebeck) (Hymenoptera: Braconidae) from natural populations was directly observed in a highbush blueberry, Vaccinium corymbosum L., plantation. More D. alloeum were observed alighting on blueberry fruit clusters infested with Rhagoletis mendax Curran larvae than were observed alighting on uninfested blueberry fruit clusters 80 cm away. Approximately equal numbers of D. alloeum alighted on uninfested blueberries that were mechanically damaged versus undamaged. The majority of D. alloeum females were attracted to host-infested blueberries 15 to 21 days after R. mendax females had oviposited into fruit. Female D. alloeum spent more time alighting on R. mendax-infested blueberry fruit clusters than on uninfested blueberry clusters 80 cm away. There was no difference in the duration of time spent by D. alloeum on mechanically damaged versus undamaged uninfested blueberries. The data herein are an initial step toward elucidating t...

Host-Habitat Location and Host Location By Diachasma Alloeum Muesebeck (Hym.; Braconidae), a Parasitoid of Rhagoletis Pomonella Walsh (Dipt.; Tephritidae)

Three laboratory experiments were designed to elucidate some of the stimuli that are involved in host micro-habitat searching, the stimulation of host-searching behaviour and in host location by Diachasma alloeum. Visual orientation was found to play an important role in the location of fruits (Crataegus mollis) by D. alloeum. Equal numbers of landings were obtained on host-infested and uninfested haws. A description is presented of the host-searching behaviour by D. alloeum on haws. It was found that probing activity and duration of stay on the fruit are strongly influenced by the presence of a Rhagoletis pomonella larva in the fruit. A quantification was made of the accuracy with which D. alloeum probes the fruit in search of hosts. It is concluded that host movement is the prime stimulus for the location of hosts. Females on haws containing a moving larva exhibited non-random probing. It was found that parasitization of the host by D. alloeum is preceeded by paralyzation of the host. When paralyzed larvae were offered in the same set-up, D. alloeum exhibited random probing.

PARASITOIDS EMERGING FROM PUPARIA OF RHAGOLETIS POMONELLA (DIPTERA: TEPHRITIDAE) INFESTING HAWTHORN AND APPLE IN CONNECTICUT

AbstractBiosteres melleus (Gahan), Diachasma alloeum (Muesebeck), D. ferrugineum (Gahan), Opius canaliculatus Gahan, O. downesi Gahan (all Braconidae), and an undescribed Psilus sp. (Diapriidae) emerged from puparia of Rhagoletis pomonella (Walsh) collected in Connecticut during 1977 and 1978. Percentage parasitism ranged from 7.9 to 36.8% in flies on hawthorn and from 0.0 to 23.9% in flies on apple. It exceeded 5.0% in only 5 (22.7%) of 22 samples from apple. Higher rates of parasitism usually occurred at sites where other hosts of apple maggot parasitoids probably infested fruits on nearby plants.