Lyophilization of lepidopteran midguts: a preserving method for Bacillus thuringiensis toxin binding studies

Binding assays with brush border membrane vesicles (BBMV) from insect midguts are commonly used in the study of the interactions between Bacillus thuringiensis Cry toxins and their receptors. Collaboration between laboratories often require that frozen insect samples are sent in dry ice. Because of customs restrictions and delays, sample thawing is always a risk and often the biological material becomes ruined during shipping. We have tested lyophilization as an alternative method for preserving insect midguts for binding studies with B. thuringiensis Cry toxins. For this purpose, BBMV were prepared from both frozen and lyophilized midguts from three lepidopteran species: Spodoptera exigua, Manduca sexta, and Helicoverpa armigera. Higher membrane protein recovery was always obtained from lyophilized midguts compared to frozen midguts, and similar membrane marker enzyme activities were found in BBMV from either treatment. Comparable equilibrium dissociation constants and binding site concentrations, calculated from binding experiments with labeled (125)I-Cry1Ab toxin, were found using BBMV from either method. In the light of these results, lyophilization is a good preserving method of lepidopteran midguts to study binding of B. thuringiensis Cry toxins.

Physiological and molecular interaction in the host-parasitoid system Heliothis virescens-Toxoneuron nigriceps: current status and future perspectives

Toxoneuron nigriceps (Viereck) (Hymenoptera, Braconidae) is an endophagous parasitoid of the tobacco budworm Heliothis virescens (F.) (Lepidoptera, Noctuidae). Parasitized H. virescens larvae are developmentally arrested and show a complex array of pathological symptoms ranging from the suppression of the immune response to an alteration of ecdysone biosynthesis and metabolism. Most of these pathological syndromes are induced by the polydnavirus associated with T. nigriceps (TnBV). An overview of our recent research work on this system is described herein. The mechanisms involved in the disruption of the host hormonal balance have been further investigated, allowing to better define the physiological model previously proposed. A functional genomic approach has been undertaken to identify TnBV genes expressed in the host and to assess their role in the major parasitoid-induced pathologies. Some TnBV genes cloned so far are novel and do not show any similarity with genes already available in genomic databases, while others code for proteins having conserved domains, such as aspartic proteases and tyrosine phosphatases. Sequencing of the entire TnBV genome is in progress and will considerably contribute to the understanding of the molecular bases of parasitoid-induced host alterations.

Effect of exposure method to Beauveria bassiana and conidia concentration on mortality, mycosis, and sporulation in cadavers of Chilo partellus (Lepidoptera: Pyralidae)

The effects of exposure methods, conidial concentrations, and temperature on mortality, mycosis and sporulation in second instar Chilo partellus cadavers infected by Beauveria bassiana was investigated in laboratory studies. Larvae directly sprayed with conidia, exposed to conidia-treated leaves, and dipped into conidial suspension resulted in high mortality (98-100%). The longest LT50 (3.5 days) and days to mortality (2.6 days) were observed in the treated-leaves exposure method. The shortest LT50 (1 day) and days to mortality (1 day) were recorded for the dipping method. With increasing conidial concentrations, there were decreasing LT50 and days to mortality. Larvae exposed to treated leaves and larvae directly sprayed with conidial suspensions produced high mycoses in cadavers. Exposure of larvae to treated-leaves resulted in high sporulation. At lower concentrations of conidia, both mycosis and sporulation in cadavers were high. The optimum temperature for mycosis was 20 and 15 degrees C for sporulation.

Wasp parasitoid disruption of host development: implications for new biologically based strategies for insect control

Wasp parasitoids use a variety of methods to commandeer their insect hosts in order to create an environment that will support and promote their own development, usually to the detriment of the host insect. Parasitized insects typically undergo developmental arrest and die sometime after the parasitoid has become independent of its host. Parasitoids can deactivate their host's immune system and effect changes in host hormone titers and behavior. Often, host tissues or organs become refractory to stimulation by tropic hormones. Here we present an overview of the manipulative capabilities of wasp-injected calyx fluid containing polydnaviruses and venom, as well as the parasitoid larva and the teratocytes that originate from the serosal membrane that surrounds the developing embryo of the parasitoid. Possibilities for using regulatory molecules produced by the parasitoid or its products that would be potentially useful in developing new, environmentally safe insect control agents are discussed.

Juvenile hormone synthesis, metabolism, and resulting haemolymph titre in Heliothis virescens larvae parasitized by Toxoneuron nigriceps

Last instar larvae of the tobacco budworm, Heliothis virescens F., fail to pupate and have little 20-hydroxyecdysone when parasitized by Toxoneuron nigriceps (Viereck). In this paper, we extend these observations to juvenile hormone (JH) to determine if parasitism by this wasp affects other endocrine systems. To this end, we compared the production of JH by corpora cardiaca-corpora allata complexes (CC-CA), the metabolism of JH by haemolymph enzymes, and the haemolymph titre of JH in parasitized and non-parasitized control larvae of H. virescens during the last larval instar. CC-CA from parasitized and control larvae had similar peaks of JH synthesis on day 1 of the fifth instar, with JH II accounting for more than 90% of total JH in both groups. On subsequent days, JH synthesis dropped to undetectable levels more quickly in non-parasitized controls than in parasitized larvae. JH metabolism by haemolymph of parasitized and control animals increased from low levels on day 1 of the fifth instar to high levels on days 2 and 3 of the instar. JH metabolism was significantly higher in control larvae than in parasitized larvae. After day 3, JH metabolism decreased in both groups, but was significantly higher in parasitized larvae. The major metabolite of JH in both groups was JH acid, though traces of JH diol and JH acid diol were also detected. The haemolymph titre of JH in both groups peaked on day 1 of the fifth instar and, similar to the synthesis of JH by CC-CA, decreased more rapidly in control larvae. As a result, non-parasitized animals had significantly lower JH titres on day 2. The higher JH titres observed in parasitized larvae during the early fifth instar may contribute to their developmental arrest. The possible role of these JH alterations in the host developmental and metabolic redirection is discussed and a more comprehensive physiological model accounting for host-parasitoid interactions is proposed.

Morphological and genomic characterization of the polydnavirus associated with the parasitoid wasp Glyptapanteles indiensis (Hymenoptera: Braconidae)

Glyptapanteles indiensis polydnavirus (GiPDV) is essential for successful parasitization of the larval stage of the lepidopteran Lymantria dispar (gypsy moth) by the endoparasitic wasp Glyptapanteles indiensis. This virus has not been characterized previously. Ultrastructural studies of GiPDV showed that virions had a rod-like or rectangular form and each contained as many as ten nucleocapsids enclosed by a single unit membrane envelope. Field inversion gel electrophoresis (FIGE) analysis of the virus genomic DNA revealed that GiPDV had a segmented genome composed of 13 dsDNA segments, ranging in size from approximately 11 kb to more than 30 kb. Four genomic segments were present in higher molar concentration than the others. Further characterization of the GiPDV genome yielded several cDNA clones which derived from GiPDV-specific mRNAs, and Northern blot analysis confirmed expression of isolated cDNA clones in the parasitized host. Each was present on more than one GiPDV genomic DNA segment, suggesting the existence of related sequences among DNA segments. It has been proposed previously that in polydnavirus systems, genome segmentation, hypermolar ratio segments and segment nesting may function to increase the copy number of essential genes and to increase the levels of gene expression in the absence of virus replication. The present data support this notion and suggest that GiPDV morphology and genomic organization may be intrinsically linked to the function and evolutionary strategies of the virus.

Interactions of two idiobiont parasitoids (Hymenoptera: Ichneumonidae) of codling moth (Lepidoptera: Tortricidae) with the entomopathogenic nematode Steinernema carpocapsae (Rhabditida: Steinernematidae)

Simultaneous use of parasitoids and entomopathogenic nematodes for codling moth (CM) control could produce an antagonistic interaction between the two groups resulting in death of the parasitoid larvae. Two ectoparasitic ichneumonid species, Mastrus ridibundus and Liotryphon caudatus, imported for classical biological control of cocooned CM larvae were studied regarding their interactions with Steinernema carpocapsae. Exposure of M. ridibundus and L. caudatus developing larvae to infective juveniles (IJs) of S. carpocapsae (10 IJs/cm2; approximately LC(80-90) for CM larvae) within CM cocoons resulted in 70.7 and 85.2% mortality, respectively. However, diapausing full grown parasitoid larvae were almost completely protected from nematode penetration within their own tightly woven cocoons. M. ridibundus and L. caudatus females were able to detect and avoid ovipositing on nematode-infected cocooned CM moth larvae as early as 12h after treatment of the host with IJs. When given the choice between cardboard substrates containing untreated cocooned CM larvae and those treated with an approximate LC95 of S. carpocapsae IJs (25 IJs/cm2) 12, 24, or 48h earlier, ovipositing parasitoids demonstrated a significant preference for untreated larvae. The ability of these parasitoids to avoid nematode-treated larvae and to seek out and kill cocooned CM larvae that survive nematode treatments enhances the complementarity of entomopathogenic nematodes and M. ridibundus and L. caudatus.

Seasonal variation and infestation incidence by Marmara gulosa (Lepidoptera: Gracillariidae) on grapefruit in the Coachella Valley, California

The population dynamics of citrus peelminer, Marmara gulosa Guillén and Davis, were investigated in 1996-1999 in commercial grapefruit groves in the Coachella Valley, CA. The first generation of the peelminer on new fruit was observed in early June 1998; larval densities of peelminer increased at the beginning of summer and peaked in late July to early August in most years, then decreased, remaining low by the end of the summer and rest of the year. Three parasitoids were identified, with Cirrospilus coachellae Gates in highest numbers in all groves and years. Numbers of larvae parasitized by C. coachellae increased by midsummer in most groves, coinciding with the decline in densities of the citrus peelminer. Miners continued to develop on fruit left from previous harvest in June. Miners preferred the lower half canopy of the trees. Parasitism and availability of fruit for development are major components in the dynamics of the citrus peelminer.

Effects of GNA transgenic sugarcane on life history parameters of Parallorhogas pyralophagus (Marsh) (Hymenoptera: Braconidae), a parasitoid of Mexican rice borer

Parallorhogas pyralophagus (Marsh) is the principal parasitoid of the Mexican rice borer [Eoreuma loftini (Dyar)], the primary pest of sugarcane in south Texas. Insect resistant transgenic sugarcane producing Galanthus nivalis agglutinin (GNA) was developed to improve control of E. loftini. The present laboratory study addressed whether over two consecutive generations transgenic sugarcane delivered via artificial diet has adverse host-mediated effects on P. pyralophagus life history parameters. The results of this study showed that a number of life history parameters were affected by transgenic sugarcane, whereas others were not affected, and that effects varied between generations. In the first generation, adult longevity was increased by approximately 2 d, and cocoon to adult and egg to adult developmental times were prolonged by approximately 1 d in parasitoids exposed to transgenic sugarcane, whereas effects were not evident on adult size; egg load; egg to cocoon developmental time; rates of gain of longevity and egg load with adult size; and egg, larval, and pupal mortality. However, in the second generation, adult longevity was reduced by approximately 3 d, adult size by approximately 5%, egg load by approximately 24%, and rate of gain of longevity with adult size by approximately 21%, whereas effects were not evident on the rate of gain of egg load with adult size. It was concluded that although GNA transgenic sugarcane, ingested via E. loftini tissues, was not acutely toxic to P. pyralophagus, the sublethal effects on life history parameters measured in this study must be considered in a broader context to determine their possible ecological significance.

Interactions between parasitized and unparasitized conspecifics: parasitoids modulate competitive dynamics

Parasitism influences many aspects of a host's behavior and physiology. Therefore, parasitism is also likely to influence the competitive ability of the host. Field populations of phytophagous insects are often a mix of parasitized and unparasitized conspecifics and the inclusion of parasitism in their competitive dynamics may alter expected outcomes. We investigated the influence of parasitism by the hymenopteran parasitoid Phanerotoma franklini Gahan on the competitive interactions among larvae of its host Acrobasis vaccinii Riley. We found that parasitized larvae were poorer competitors and required less food to complete development compared to unparasitized larvae. To examine the influence of parasitism on the competitive dynamics of this system, we constructed an individual-based model parameterized with our laboratory data. The model examined the role of resource availability and parasitism rate on larval survival. The model suggests that parasitized larvae (and, hence parasitoids) experience higher levels of mortality from competition than unparasitized larvae. Further, the model also suggests that the decreased consumption of resources by parasitized larvae results in a decline in the occurrence of competition as the parasitism rate increases. We suggest that these observations may be general to many parasitoid-host systems.

The characterization of microsporidian isolates (Nosematidae: Nosema) from five important lepidopteran pests in Taiwan

Microsporidian isolates from five lepidopteran pests-Spodoptera litura, Spodoptera exigua, Helicoverpa armigera, Plutella xylostella, and Pieris spp.-were compared by spore morphology, infectivity to S. litura, Western-blot banding patterns, the sequences of small subunit rRNA gene (SSUrRNA sequence), and random amplified polymorphic DNA polymerase chain reaction (RAPD-PCR). All the isolates could infect experimentally and multiply in the larvae of S. litura. The S. exigua isolate showed the highest virulence to the larvae of S. litura while the P. xylostella isolate showed the lowest. No significant differences either in spore morphology or in SSUrRNA sequences of these isolates were found. The SSUrRNA sequences of these isolates confirmed they are members of the genus Nosema. Based on the result of Western-blot hybridization with the rabbit anti-Nosema spodopterae spore antiserum, three serotypes could be distinguished: N. spodopterae (S. litura isolate) and Pi. spp. isolate; S. exigua and H. armigera isolates; and P. xylostella isolate. The amplicons of RAPD-PCR with 60 primers yielded clear patterns that were selected and used for identification and also for phylogenic analysis of these five isolates. Based on analysis by the computer, isolates could be clearly divided into three groups that were coincident with the serotypes; therefore we suggest that N. spodopterae and isolates of Pi. spp., S. exigua, and H. armigera are more closely related in phylogenesis. In addition, in the amplification with the Nosema bombycis specific primer set, only DNAs from P. xylostella isolate and N. bombycis yielded amplicons. Therefore, we suggest that four isolates, excluding the P. xylostella isolate, are N. spodopterae, and the taxonomic position of P. xylostella isolate needs to be elucidated.

What determines host range in parasitoids? An analysis of a tachinid parasitoid community

Despite the vast diversity of parasitic insects and their importance in natural and agricultural communities, our knowledge of what determines their patterns of association with hosts remains sparse. Unlike most parasites that tend to be specialized, parasitoid flies in the family Tachinidae exhibit a broad spectrum of host-specificity, with many species attacking a wide range of hosts. This variability in host-specificity makes them a useful model for examining the ecological and historical factors that determine host associations. We analyzed data collected from a 5-year rearing program of Lepidoptera in southern Arizona to investigate the factors that influence tachinid-host associations. After controlling for a strong effect of sample size, a significant portion of the remaining variance in host range was explained by differences among phylogenetic groups of tachinids and/or their correlated reproductive strategies. Relatively specialized tachinids tended to be associated with monophagous or narrowly oligophagous hosts and attacked them at relatively high frequencies, a pattern we suggest is related to host location efficiency. Cluster analysis indicated that host abundance, gregariousness, food-plant type, and morphology are all important determinants of tachinid host use. Little concordance was found between how tachinid species cluster according to characteristics of their hosts and their estimated phylogenetic relationships. Together, the results of this study suggest that ecological factors are important determinants of host use in these parasitoids and although phylogenetic history may influence the range of hosts used, its power to explain the ecological or taxonomic character of hosts used appears limited.

Passive evasion of encapsulation in Macrocentrus cingulum Brischke (Hymenoptera: Braconidae), a polyembryonic parasitoid of Ostrinia furnacalis Guenée (Lepidoptera: Pyralidae)

The hymenopteran Macrocentrus cingulum usually deposits one egg into the larval body cavity of lepidopteran Ostrinia furnacalis, and the egg subsequently splits into several dozens of embryos during its development. How the parasitoid eggs and embryos avoid encapsulation by the host's immune response remains unknown. We compared hemocyte counts, morphologies and behaviors between unparasitized O. furnacalis larvae, and larvae parasitized by M. cingulum. No distinct differences were observed. Sephadex A-25 beads elicited a strong encapsulation response when injected into the parasitized host larvae, which indicates that parasitism by M. cingulum does not affect host's cellular immunity. However, there were significant differences in the host's encapsulation reactions towards injected eggs from different sources. Injected M. cingulum mature eggs excised from the lateral oviducts of the female wasps were not encapsulated, while immature eggs or driselase treated mature ones provoked an encapsulation response within 2 h after injection. Inspection of eggs by transmission electron microscopy revealed that the driselase collapsed the surface fibrous layer of the eggs, indicating that surface fibrous layer may play a role in protecting eggs from host's immune attack.

Toxoneuron nigriceps polydnavirus encodes a putative aspartyl protease highly expressed in parasitized host larvae

Toxoneuron nigriceps (Viereck) (Hymenoptera: Braconidae) is an endophagous parasitoid of larval stages of the tobacco budworm, Heliothis virescens (F.) (Lepidoptera: Noctuidae). This parasitoid is associated with a polydnavirus (TnBV), injected at oviposition along with the egg, and involved in the disruption of host immune reaction and endocrine balance. This paper reports the molecular characterization of TnBV2, one of the most abundant genes in the TnBV genome. TnBV2 expression produces a mature 0.6 kb transcript in fat body, prothoracic glands and haemocytes, as early as 6 h after parasitoid oviposition. Only in haemocytes a specific longer transcript of 2.5 kb is found 24 h after parasitization. The putative translation product of TnBV2 contains a retroviral type aspartyl protease domain. The possible origin and functional role of this TnBV gene are discussed.

Impact of a novel species of Nosema on the southwestern corn borer (Lepidoptera: Crambidae)

A study was undertaken to elucidate the impact of an undescribed Nosema sp. on the southwestern corn borer (SWCB; Diatraea grandiosella Dyar). The Nosema sp. (isolate 506) included in the study was isolated from an overwintering SWCB larva in Mississippi. It was highly infectious per os, with a median infective dose of 2.0 x 10(3) spores per larva. Even at the highest dosage tested (10(7) spores per larva), minimal mortality (< or = 3%) was observed in infected larvae, pupae, and adults reared in the laboratory on an artificial diet. However, infected pupae (0- and 7-d-old) were smaller, and the time to adult eclosion from pupation was slightly increased. Furthermore, the number of eggs produced by infected SWCB female moths substantially decreased (32%), and this effect was most pronounced on day 2, when the greatest number of eggs were oviposited by infected and noninfected moths. For eggs produced by infected females mated with infected males, hatch was slightly decreased by 16 and 15% for eggs laid on days 2 and 3, respectively. In addition, egg hatch was reduced in eggs oviposited by noninfected females mated with infected males on day 3. A low prevalence of infection (< 6%) was observed in the F1 generation originating from infected females mating with noninfected males, from noninfected females mating with infected males, and from infected females mating with infected males. Nosema 506 spores were observed in the proximity of reproductive tissues of infected female and male moths. Spores also were detected on the chorion surface and within eggs laid by infected females. Furthermore, 1-11% of larvae hatching from surface-sterilized eggs were infected by Nosema 506 indicating a transovarial mechanism of transmission.

[Parasitic systems of Microsporidia: descriptions and terminology questions]

Three parasitic systems of Microsporidia are described: the system of monoxenic Vairimorpha mesnili with paraxenic hosts presented lepidopteran and hymenopteran species; the system of dixenic Amblyospora sp. with metaxenic hosts presented bloodsucking mosquitoes and crustaceans and the system of Metchnikovella sp. as parasite of other obligate parasite. The last case is characterized by very intimate interrelations between hyperparasite (microsporidian species), obligate parasite--host of Microsporidia (gregarine) and hyperhost--host of gregarine (polychaeta). This hyperparasite system is exclusive case of parasitic systems. Parasitic and hyperparasitic systems reflects a population level of host-parasite interactions. On biocenotic level many other organisms such as predators, vectors and reservators of invasion stages of Microsporidia affect parasitic systems giving a chance to one of the members of the system (to the host or to the parasite). These organisms form epiparasitic system. In all cases of the parasitic systems there are two-way communications between parasites and their hosts. In systems on biocenotic level--parasitic consortium--members of epiparasitic systems acts on parasitic systems, but members of parasitic systems don't affect epiparasitic systems.

Gustatory sensilla sensitive to protein kairomones trigger host acceptance by an endoparasitoid

Proteins isolated from the host cocoon of Acrolepiopsis assectella (Lepidoptera: Yponomeutoidea) act as kairomones for host acceptance by the endoparasitoid wasp Diadromus pulchellus Wesmael (Hymenoptera: Ichneumonidae). In this study, morphological, ultrastructural and electrophysiological studies were carried out in order to identify the contact chemoreceptive sensilla on the parasitoid antennae that perceive the protein kairomones. Three types of sensillum on the antennae of the females were found to have a chemosensory function. The receptor cell(s) of one sensillar type were shown to give a positive electrophysiological response to protein kairomones. This sensillar type is apically multiporous and female specific. Consequently, this sensillum could be the one implicated in the perception of the protein kairomone that triggers the host-acceptance behaviour of D. pulchellus females.

Hormonal implication in Bracon-venom-induced paralysation of the host larva of Corcyra cephalonica (Lepidoptera: Pyralidae)

To facilitate oviposition, the ectoparasite Bracon hebetor, injects its venom, a paralysing toxin, to the host Corcyra larva that ultimately dies without showing any metamorphic change, even if allowed to remain unparasitised. At the initial stage of venom injection the rate of heartbeat of the host becomes abruptly high. This has been explained from the synergistic action of the substances of poison gland and calyx. The paralysed larvae subsequent to envenomization die within 240 hr. Application of hydroprene as single dose or with a booster dose after paralysation mostly increases the survival period considering heart beat as the index. The predicted value of survival period (714.4 hr), determined from a fitted equation obtained from the relationship between heart beat and survival period, indicates that a 100 microg treatment/larva with a booster dose of 50 microg/larva most effectively lengthens the period. It is concluded that the venom-induced physiological dysfunction of the immobilised larvae, as indicated in the rate of heart beat and survival period, though can be recovered to some extent after the application of juvenoids, there cannot occur any metamorphic change of these larvae. The parasitoid, therefore, succeeds in completing its development and metamorphosis by arresting the development of its host through an indirect hormonal suppression. The findings indicate an endocrine implication in host-parasite relationship in insect.

Induced parasitoid attraction by Arabidopsis thaliana: involvement of the octadecanoid and the salicylic acid pathway

Plants can use indirect defence mechanisms to protect themselves against herbivorous insects. An example of such an indirect defence mechanism is the emission of volatiles by plants induced by herbivore feeding. These volatiles can attract the natural enemies of these herbivores, for example, parasitoid wasps. Here, it is shown that the octadecanoid and the salicylic acid pathways are involved in the induced attraction of the parasitoid wasp Cotesia rubecula by Arabidopsis thaliana infested with the herbivore Pieris rapae. Besides exogenous application of jasmonic acid or salicylic acid, use is also made of transgenic Arabidopsis that do not show induced jasmonic acid levels after wounding (S-12) and transgenic Arabidopsis that do not accumulate salicylic acid (NahG). Treatment of Arabidopsis with jasmonic acid resulted in an increased attraction of parasitoid wasps compared with untreated plants, whereas treatment with salicylic acid did not. Transgenic plants impaired in the octadecanoid or the salicylic acid pathway were less attractive than wild-type plants.

Inheritance of an oviposition behavior by an egg parasitoid

A quantitative genetic study revealed genetic and environmental sources of variance in percentage parasitism of European corn borer egg masses and secondary sex ratios by Trichogramma nubilale. Full and half-sib groups of T. nubilale were obtained from a nested mating design, which permitted the partitioning of the variance of T. nubilale parasitism of European corn borer egg masses into additive genetic variance, maternal/dominant variance and environmental variance. A mother-daughter regression of the percentage of an egg mass parasitized allowed a determination of the direction of a potential response to selection in the event of maternal effects. No or very little additive genetic effects were associated with the percentage of eggs within a mass parasitized and secondary sex ratios, but a significant amount of the variance for both traits had a maternal and/or dominant genetic source. The relationship between mothers and daughters in egg mass parasitism was positive, and 55.4% of the progeny of a given mother had behaviors that resemble their mother. Most of the variance had an environmental and/or unknown genetic source implying potentially high phenotypic plasticity associated with all these traits. The presence of maternal effects and phenotypic plasticity could have multiple and complex effects on progeny characters and potential responses to selection.

Visual control of host pursuit in the parasitoid fly Exorista japonica

The tachinid fly Exorista japonica is a parasitoid of many kinds of lepidopterous larvae. After encountering a suitable host, the fly pursues the crawling larva on foot using visual cues to guide it. To investigate the visual control of host pursuit, we observed and videotaped pursuits of a host, the common armyworm Mythimna separata, for frame-by-frame analysis. Observation was performed in sunlight and under illumination from a fluorescent lamp. The fly pursued hosts discontinuously with a repeated stop-and-run motion. During a run, its movements consisted of rotation, forward translation and sideways translation. Rotation during a run was positively correlated with the angular position of the host’s head. The direction of translation depended on the angular position of the host’s head. Forward translation was negatively correlated with the visual angle subtended by the host. These results suggest that the fly orients and walks towards the leading edge of a moving target. There was little difference in the results between sunlight and illumination from a fluorescent lamp.

Herbivore-induced volatile production by Arabidopsis thaliana leads to attraction of the parasitoid Cotesia rubecula: chemical, behavioral, and gene-expression analysis

Many plant species defend themselves against herbivorous insects indirectly by producing volatiles in response to herbivory. These volatiles attract carnivorous enemies of the herbivores. Research on the model plant Arabidopsis thaliana (L.) Heynh. has contributed considerably to the unraveling of signal transduction pathways involved in direct plant defense mechanisms against pathogens. Here, we demonstrate that Arabidopsis is also a good candidate for studying signal transduction pathways involved in indirect defense mechanisms by showing that: (1) Adult females of Cotesia rubecula, a specialist parasitic wasp of Pieris rapae caterpillars, are attracted to P. rapae-infested Arabidopsis plants. (2) Arabidopsis infested by P. rapae emits volatiles from several major biosynthetic pathways, including terpenoids and green leaf volatiles. The blends from herbivore-infested and artificially damaged plants are similar. However, differences can be found with respect to a few components of the blend, such as two nitriles and the monoterpene myrcene, that were produced exclusively by caterpillar-infested plants, and methyl salicylate, that was produced in larger amounts by caterpillar-infested plants. (3) Genes from major biosynthetic pathways involved in volatile production are induced by caterpillar feeding. These include AtTPS10, encoding a terpene synthase involved in myrcene production, AtPAL1, encoding phenylalanine ammonia-lyase involved in methyl salicylate production, and AtLOX2 and AtHPL, encoding lipoxygenase and hydroperoxide lyase, respectively, both involved in the production of green leaf volatiles. AtAOS, encoding allene oxide synthase, involved in the production of jasmonic acid, also was induced by herbivory.

Selfish element maintains sex in natural populations of a parasitoid wasp

Genomic conflicts between heritable elements with different modes of inheritance are important in the maintenance of sex and in the evolution of sex ratio. Generally, we expect sexual populations to exhibit a 1:1 sex ratio. However, because of their biology, parasitoid wasps often exhibit a female-biased sex ratio. Sex-ratio distorters can further alter this optimum, sometimes leading to the complete loss of sexual reproduction. In the parasitoid wasp Trichogramma kaykai ca. 4-26% of females in field populations are infected with a bacterial sex-ratio distorter, Wolbachia, allowing virgin mothers to produce daughters. In some micro-Hymenoptera these infections have led to the complete loss of sex, but in field populations of T. kaykai the proportion of individuals infected remains relatively stable. We tested several hypotheses to explain this low infection level, including inefficient and horizontal transmission of Wolbachia, suppressor genes negating the effect of Wolbachia and the presence of male-biasing sex-ratio distorters. Here, a male-biasing sex-ratio distorter, a parasitic B chromosome, causing females to produce only sons, keeps the frequency of Wolbachia low. The male-biasing factor of T. kaykai is the second known case of a B chromosome manipulating the reproduction of a parasitoid wasp.

Effects of Glyptapanteles liparidis (Hym.: Braconidae) parasitism, polydnavirus, and venom on development of microsporidia-infected and uninfected Lymantria dispar (Lep.: Lymantriidae) larvae

Effects of parasitism, polydnavirus, and venom of the endoparasitoid Glyptapanteles liparidis on Lymantria dispar larvae infected with the microsporidium Vairimorpha sp. and uninfected hosts were studied. We tested the impact on growth and development of hosts, as well as on microsporidian infection. Both parasitism and polydnavirus/venom treatment alone caused a slight increase in growth rate and relative growth rate in uninfected fourth instar hosts. This effect was more pronounced with the addition of Vairimorpha infection. With no parasitism, however, infection reduced host growth markedly. Microsporidiosis delayed larval molts of L. dispar, and additional polydnavirus/venom treatment or parasitization induced significantly earlier molting. Polydnavirus/venom treatment of uninfected L. dispar resulted in prolonged larval development due to supernumerary molts and in higher pupal mortality. Infected larvae treated with polydnavirus/venom died earlier than infected larvae that were not treated and produced more Vairimorpha spores per unit fresh mass of the host.

Effect of dietary cowpea trypsin inhibitor (CpTI) on the growth and development of the tomato moth Lacanobia oleracea (Lepidoptera: Noctuidae) and on the success of the gregarious ectoparasitoid Eulophus pennicornis (Hymenoptera: Eulophidae)

Cowpea trypsin inhibitor (CpTI) was shown to have a deleterious effect on the growth and development of larvae of the tomato moth, Lacanobia oleracea, when incorporated in artificial diet (2.0% of soluble protein) and expressed in transgenic potato leaf (up to 1.0% of soluble protein). The effect of CpTI on parasitism of L oleracea by the ectoparasitoid Eulophus pennicornis was investigated. The parasitic success of the wasp was reduced by the presence of CpTI in the diet of the host and, in the case of transgenic potato leaves expressing the transgene protein, was collated with the length of time the host fed on the diet prior to parasitism. In all cases the proportion of hosts parasitised when fed CpTI-containing diets was reduced when compared with controls, although these differences were only significant when hosts were fed from the third instar on the transgenic potato leaves. Parasitoid progeny that developed on L oleracea reared on CpTI-containing diets, however, were not adversely affected. These results show that, whilst expression of CpTI in transgenic potato plants confers resistance to the lepidopterous pest L oleracea, adverse effects on the ability of the ectoparasitoid E pennicornis to parasitise this moth species successfully may also occur. These results are discussed in relation to the potential impact of transgenic crops on beneficial biological control agents.

[Lifetable of cotton bollworm under different control condition]

The lifetables of 3rd and 4th generation of cotton bollworm Helicoverpa armigera Hubner were established by action factors under four different control conditions. The results showed that under natural control, the egg parasitic rates of 3rd and 4th cotton bollworm were 4.39% and 1.19%, the predatory rates were 21.11% and 15.80%, and the larvae parasitic rates were 19.34% and 16.20% respectively. The indexes of population trend were only 0.0032 and 0.0014 respectively, after using selective pesticides IKI and Bt to control cotton bollworm. Though the index of population trend decreased to 48.66% and 61.67% after contantly praying chemical pesticides, the number of predators also decreased to 23.48% and 41.26% respectively. Transgenic Bt cotton could inhibit the population increase of cotton bollworm, but had no effect on predators. The parasitic rates of 3rd and 4th cotton bollworm on Transgenic Bt cotton were 51.14% and 0% respectively, as compared to control.

[Study on the biology feature and pathogenicities to silkworm of a microsporidium isolated from Barathra brassicae L]

A microsporidium (called as Bab-M) was isolated from Barathra brassicae L. captured from suburban vegetable plot of Guang Zhou. The spores were long-ovoid in shape and 4.02 +/- 0.36 microns x 1.99 +/- 0.36 microns in size. Immunologically the microsporidium shared spore surface specific antigen(s) with N. bombycis. The ultrastructure and life cycle of Bab-M were similar to that of N. b.. The rate of transovarian transmission was high. The initial conclusion was that Bab-M should be referred to as Nosema bombycis, but there was variation between them.

Environmental factors affecting sexual differentiation in the entomopathogenic nematode Heterorhabditis bacteriophora

The present study was aimed at determining the influence of various environmental factors on sex differentiation (SD) in the entomopathogenic nematode Heterorhabditis bacteriophora HP88 strain, under in vivo and in vitro culture conditions. Injection of individual nematodes into last instars of Galleria mellonella resulted in development of a similar number of females and hermaphrodites (35-40%) and 20-25% males. Increasing the number of nematodes injected into the insect did not change these proportions. In smaller insects (0.7-1.5 cm long), an increase in the proportion of hermaphrodites was recorded as compared with larger size cadavers (2.4-2.7 cm long). When individual hermaphrodites were placed on NGM, the proportion of hermaphrodites, females and male progeny was 63%, 31%, and 6%, respectively. Rearing on richer medium ("Dog-food" agar) resulted in reduction in the proportion of hermaphrodites. Nematodes introduced to the symbiotic bacterium obtained from other nematode strains (IS-5 and IS-33) developed similarly to the culture reared on the HP88 bacteria. Rearing the nematodes at a temperature range between 21 degrees C to 30 degrees C also did not have a significant effect on the sexual differentiation among nematodes cultured on NGM. The proportion of hermaphrodites increased as the starvation period of hatching nematode juveniles lengthened (>6 hr). The data obtained in the present study strongly suggest that the main factor affecting sex differentiation in H. bacteriophora is the nutrition source. The practical and biological implications of the results are discussed.

The karyotype of the parasitoid Chelonus insularis Cresson (Hymenoptera, Braconidae, Cheloninae)

The karyotype of Chelonus insularis (Hymenoptera, Braconidae, Cheloninae) is described. The males show an haploid number of seven chromosomes and the females a diploid number of fourteen chromosomes, confirming haplo-diploid sex determination. Comparisons of these results with karyotypes of other species of the same family were done and a possible mechanism involved in the karyotype evolution of this species is discussed.

Changes of haemolymph protein profile in the larva of Pericallia ricini (Fabricius) parasitised by the Braconid Wasp, Apanteles taragamae Viereck (Hymenoptera: Braconidae)

Parasitism by the braconid wasp, A. taragamae caused alterations in the haemolymph polypeptides of woolly bear larvae of P. ricini. Analysis of haemolymph proteins by SDS-PAGE and densitometry showed that the quantities of haemolymph proteins were reduced dramatically in the parasitised larvae. Simultaneously, parasitism induced large amount of 95 kDa polypeptides in the haemolymph of the parasitised larvae. Also, a remarkable induction of 43 and 45 kDa polypeptides which are not detectable in non-parasitised larvae appeared in the parasitised larvae.

Influence of insect larvae and seedling roots on the host-finding ability of Steinernema feltiae (Nematoda: Steinernematidae)

The ability of nematode foragers to locate appropriate insect hosts is essential to their performance as successful biological control agents. We investigated the host-finding ability and chemotaxis of Steinernema feltiae in the presence of cues from Galleria mellonella larvae and tomato and radish seedling roots, given individually and in combination, over 120 min. In agar arena tests, infective juveniles of S. feltiae responded positively to unsterilized and sterilized larvae and tomato seedling roots and negatively to unsterilized radish seedling roots. This negative response changed following surface sterilization of these seeds. The response of the infective juveniles to a combination of larva and seedling roots depended on the nature of the individual cues and their proximity to each other. For example, the response of the nematodes to a combination of cues from a sterilized larva and an unsterilized tomato seedling root placed adjacent to each other was intermediate to the separate responses to cues from a sterilized larva and an unsterilized tomato seedling root given individually. However, the response of the nematodes to a combination of adjacent cues from a sterilized larva and an unsterilized radish seedling root was not significantly different from that to cues from an unsterilized radish seedling root given individually. When the cues from the larva and seedling roots were separated by a distance, the response of the nematodes favored the larva. However, this positive effect was lessened when the larva was surface sterilized as compared with the response to the unsterilized larva. The altered responses of the infective juveniles to target cues following surface sterilization suggest that cues from the larval cuticle and seedling roots, such as those associated with their surface microflora, may significantly influence their host-finding ability. The use of entomopathogenic nematodes as biological control agents under field applications can be improved by careful consideration of the application protocols and by the recognition that chemical alterations of the soil rhizosphere may influence their host-finding ability.

Vairimorpha imperfecta n.sp., a microsporidian exhibiting an abortive octosporous sporogony in Plutella xylostella L. (Lepidoptera: Yponomeutidae)

The microsporidian genus Nosema is characterized by development in direct control with host cell cytoplasm, diplokaryotic nuclei throughout development and disporous sporogony. The genus Vairimorpha exhibits the same features plus an octoporous sporogony producing uninucleate spores in a sporophorous vesicle. A microsporidium from diamondback moth, Plutella xylostella, falls between Nosema and Vairimorpha in that it initiates but fails to complete the octosporous sequence in this host. The name Vairimorpha imperfecta n.sp. is proposed. Merogony is mainly by formation of buds from multinucleate meronts, the buds remaining attached in chains. Diplokaryotic spores measure 4.3 x 2.0 microns (fresh) and have 15.5 coils of the polar tube in 1 rank. The octosporous sporogony is aborted owing to irregular formation of nuclear spindles, incomplete cytoplasmic fission and bizarre deposition of electron-dense episporontal secretions. Phylogenetic analyses of the sequences of the small subunit rRNA genes of V. imperfecta and of several Nosema and Vairimorpha spp. place V. imperfecta in a clade with Nosema spp. from Lepidoptera rather than in the clade containing the more typical species of Vairimorpha. It is suggested that the ancestors of the Vairimorpha/Nosema complex of species exhibited both disporous and octosporous sporogonies, as does the type species of Vairimorpha, Vairimorpha necatrix. It would follow that true Nosema spp. have lost the ability to express an octosporous sequence and that V. imperfecta is in the process of losing it. It is proposed that the genera Nosema and Vairimorpha be placed in the same family Nosematidae Labbé 1899, rather than in separate families and orders as at present.

Presence of polydnavirus transcripts in an egg-larval parasitoid and its lepidopterous host

The parasitoid Chelonus inanitus (Braconidae, Hymenoptera) oviposits into eggs of Spodoptera littoralis (Noctuidae, Lepidoptera) and, along with the egg, also injects polydnaviruses and venom, which are prerequisites for successful parasitoid development. The parasitoid larva develops within the embryonic and larval stages of the host, which enters metamorphosis precociously and arrests development in the prepupal stage. Polydnaviruses are responsible for the developmental arrest and interfere with the host's endocrine system in the last larval instar. Polydnaviruses have a segmented genome and are transmitted as a provirus integrated in the wasp's genome. Virions are only formed in female wasps and no virus replication is seen in the parasitized host. Here it is shown that very small amounts of viral transcripts were found in parasitized eggs and early larval instars of S. littoralis. Later on, transcript quantities increased and were highest in the late last larval instar for two of the three viral segments tested and in the penultimate to early last larval instar for the third segment. These are the first data on the occurrence of viral transcripts in the host of an egg-larval parasitoid and they are different from data reported for hosts of larval parasitoids, where transcript levels are already high shortly after parasitization. The analysis of three open reading frames by RT-PCR revealed viral transcripts in parasitized S. littoralis and in female pupae of C. inanitus, indicating the absence of host specificity. For one open reading frame, transcripts were also seen in male pupae, suggesting transcription from integrated viral DNA.

Physiological host specificity of microsporidia as an indicator of ecological host specificity

For most groups of biological control agents the relationship between laboratory (physiological) host range and the host range in the field (ecological host range) has not been explored empirically. The objective of our study was to investigate this relationship using the North America gypsy moth, Lymantria dispar, as a model nontarget host for microsporidia from native North American Lepidoptera. The gypsy moth, L. dispar, a native of Europe, has been established in North America for nearly 130 years and presumably exposed to many species of microsporidia from sympatric native Lepidoptera. Nevertheless, microsporidia have never been observed in North American populations of L. dispar. We conducted traditional laboratory feeding experiments using microsporidia from 20 lepidopteran host species and 1 coleopteran host species against L. dispar. Microsporidia from 18 native hosts infected L. dispar larvae. Although some of the infections were not typical of infections in the indigenous natural hosts, mature spores were produced in most of these infections. Horizontal transmission experiments, based on exposure of uninfected L. dispar larvae to infected L. dispar larvae, demonstrated that the microsporidia were far more host specific than the direct feeding experiments suggested. Of the three microsporidian biotypes that were horizontally transmitted between the nontarget L. dispar larvae, all were transmitted at very low levels. The results of our experiments provide additional evidence that the ecological host specificity of terrestrial microsporidia is much narrower than the physiological host specificity. Our studies establish the validity of using nonindigenous insect species with long-term data sets on natural enemies associated with them as a tool for testing hypotheses about host specificity.

Influence of culture method on Steinernema glaseri lipids

Entomopathogenic nematodes can be mass produced in artificial media for use as biological insecticides. Nematode in vitro media have been primarily developed on the basis of yield without fully considering nematode nutritional requirements. We investigated the quality and quantity of lipids in the entomopathogenic nematode Steinernema glaseri when grown in vivo in Popillia japonica (a natural host), Galleria mellonella (a factitious host), and in solid and liquid media. Nematode yield (infective juveniles per mg dry organic material) was 4 times higher in the in vivo compared with the in vitro cultures. Nematodes produced in vivo using P. japonica accumulated a significantly higher amount of lipids compared with nematodes grown using G. mellonella or in vitro solid and liquid methods, respectively. Fractionation of S. glaseri total lipids revealed that nematodes produced using P. japonica accumulated significantly higher phospholipids and sterols compared with other methods. C:18 fatty acids were the predominant class of lipids in S. glaseri irrespective of production method. In vivo-produced nematodes had oleic 18:1 acid as the major fatty acid, whereas in vitro-produced S. glaseri had a mixture of oleic 18:1 and linoleic 18:2 acids as the predominant fatty acids. We conclude that the lipid composition of entomopathogenic nematode is host or medium dependent. We suggest that adjusting the in vivo medium by addition of components similar to a natural host nutritional composition should improve nematode production.

Isolation, inoculation to insect host, and molecular phylogeny of an entomogenous fungus Paecilomyces tenuipes

A parasitic fungus to moth larvae and pupae, Paecilomyces tenuipes, was isolated and cultured on liquid and agar media. Fruit bodies, or synnemata, with characteristics of P. tenuipes were successfully formed on the agar medium. When pupae of wax moth, Galleria mellonella, were incubated with the conidia, all the pupae were infected and the synnemata were formed out of them. Almost the entire length of 18S rDNA of P. tenuipes was amplified by PCR and directly sequenced. Molecular phylogenetic analysis demonstrated that it belongs to the subphylum Ascomycotina, the class Pyrenomycetes, the order Clavicipitales. This result is compatible with the suggestions that P. tenuipes may be the anamorph of an entomogenous fungus of the genus Cordyceps.

Pathogenicity of axenic Steinernema feltiae, Xenorhabdus bovienii, and the bacto-helminthic complex to larvae of Tipula oleracea (Diptera) and Galleria mellonella (Lepidoptera)

The pathogenicity of the nematode-bacterium complex Steinernema feltiae-Xenorhabdus bovienii to larvae of Tipula oleracea and Galleria mellonella was investigated by injection of dauer juvenile nematodes carrying their bacterial symbiont cells (monoxenic nematodes). Axenic nematodes (free of bacteria) and the symbiotic bacteria themselves were tested. The LC50 of X. bovienii in T. oleracea was 15,700 colony forming units (CFU)/larva compared to < or = 8 CFU in G. mellonella. Xenorhabdus bovienii is apparently removed from the tipulids hemolymph, possibly by cellular defense mechanisms. Axenic nematodes were less pathogenic than monoxenic nematodes for both insects. The difference was less pronounced in G. mellonella larvae: one axenic nematode was sufficient to kill 80% in 1 day. The remaining insects found dead after 50 days were developmentally arrested. In T. oleracea 20 axenic nematodes caused 39% whereas 20 monoxenic dauer juveniles caused 90% mortality within 8 days. The data indicate that the virulence of the S. feltiae/X. bovienii complex is greater than the additive effect of the nematodes and their bacteria, further evidence for the synergistic activity of the symbiotic bacto-helminthic complex during pathogenesis.

Horizontal transmission of parthenogenesis-inducing microbes in Trichogramma wasps

Complete parthenogenesis (thelytoky) in species of the parasitic wasp Trichogramma is usually caused by the cytoplasmically inherited bacterium Wolbachia. This symbiont induces gamete duplication, which, in these haplodiploid organisms, results in all-female broods. Antibiotic treatment "cures' this condition, restoring normal sexual reproduction. Phylogenetic analysis of Wolbachia has shown that, in contrast with the strains in other host organisms (where the symbiont also induces different reproductive alterations), those in Trichogramma form a monophyletic group. This might be an indication of symbiont-host cocladogenesis. To test this, we performed comparative molecular phylogenetics on 20 parthenogenetic Trichogramma cultures and their Wolbachiae. We conclude that there is, in fact, little evidence for cocladogenesis. Instead, the phylogenetic distribution of the symbionts appears to result from occasional horizontal transmission, which probably takes place inside the hosts of Trichogramma parasitoids (usually lepidopteran eggs). This study therefore suggests that parthenogenesis is not only curable, it can sometimes be contagious also.

Natural occurrence of Bacillus thuringiensis on cabbage foliage and in insects associated with cabbage crops

Bacillus thuringiensis was isolated from the phylloplane of organically grown cabbage in one field during two growth seasons (1992-93). The frequency of B. thuringiensis varied between 0.02 and 0.67 of the total B. cereus/B. thuringiensis population, with an average of 0.11. Characterization of the B. thuringiensis isolates from foliage showed that the majority (64% of 150 isolates) belonged to serovar kurstaki, had bipyramidal crystals and toxicity towards Pieris brassicae and/or Trichoplusia ni. Other serovars were also found on the foliage but occurred at very low frequencies (one to three isolates of each serovar). Bacillus thuringiensis was also isolated from insects associated with the cabbage crop (Pieris rapae (Lep.), Delia radicum (Dip.), Syrphidae ribesii (Dip.) and Aleochara bilineata (Col.)), which were collected alive at different developmental stages in the same field. Serologically these isolates were assigned to the serovars kurstaki, aizawai, tochigiensis, colmeri and indiana/colmeri.

Use of nucleotide sequence data to identify a microsporidian pathogen of Pieris rapae (Lepidoptera, Pieridae)

Nucleotide sequence was determined for a portion of genomic DNA which spans the V4 variable region of the small subunit ribosomal RNA gene of an unidentified microsporidium from the cabbage white butterfly, Pieris rapae (174 base pairs). Comparison with equivalent sequence data obtained here for two other microsporidian species, Nosema bombycis (240 base pairs) and Nosema bombi (200 base pairs), and from the GenBank database for 11 other microsporidian species suggests that the unidentified species from P. rapae is most closely related to some Vairimorpha species. Light and electron microscopic observations of the developmental stages of this parasite were in accord with this. Infection experiments conducted at 20 and 26 degrees C demonstrated temperature-dependent dimorphism, with the production of both binucleate free spores (mean dimensions: 3.8 x 1.8 microns; 10-13 polar filament coils) and membrane-bound uninucleate octospores (mean dimensions: 3.1 x 1.9 microns). Macrospores (mean dimensions 8.0 x 2.1 microns) were also observed. Sites of infection were the gut epithelium, the Malpighian tubules, the salivary glands, and the fat body. Infections were found in all insect life stages, including the egg. This microsporidium was found to be indistinguishable from both Nosema mesnili (Paillot) and Microsporidium (Thelohania) mesnili (Paillot) and we propose that these species be combined and transferred to the genus Vairimorpha Pilley.

Microplitis demolitor polydnavirus induces apoptosis of a specific haemocyte morphotype in Pseudoplusia includens

Microplitis demolitor polydnavirus (MdPDV) is associated with Microplitis demolitor, a parasitic wasp that attacks the larval stage of the lepidopteran Pseudoplusia includens. Previously, we observed that MdPDV induced several alterations in the granular cells and plasmatocytes of P. includens, the primary haemocytes involved in regulating the cellular immune response toward M. demolitor and other parasites. In examining the mechanisms underlying immunosuppression of this host, we found that MdPDV induced apoptosis of granular cells. Granular cells underwent apoptosis both when virus was injected into the haemocoel of P. includens larvae and after infection with MdPDV in vitro. Characteristics of MdPDV-induced apoptosis included condensation of chromatin, cell surface blebbing and fragmentation of DNA into a 200 bp ladder. Although MdPDV induced changes in the ability of plasmatocytes to adhere to foreign surfaces, apoptosis of this morphotype was not observed. Examples from the literature suggest that some viruses promote their own survival by suppressing apoptosis of host cells. However, since polydnaviruses are likely to be transmitted vertically, we suggest that MdPDV promotes its own survival by inducing apoptosis of host immune cells which would otherwise kill the developing M. demolitor egg.

Polydnavirus infection inhibits synthesis of an insect plasma protein, arylphorin

The wasp Campoletis sonorensis injects a segmented, double-stranded DNA polydnavirus (CsPDV) along with its egg during parasitization of Heliothis virescens larvae. After parasitization, CsPDV protects the wasp egg and larva by selectively disabling the host's cellular immune response. Other host physiological systems including growth and development are affected to the apparent benefit of the parasite. To begin the characterization of the biochemical effects and mode of action of CsPDV on host growth, the titre of a developmentally regulated insect storage protein, arylphorin, was studied. Parasitized or virus-infected insects had substantially less circulating arylphorin than control insects. Fat bodies from parasitized larvae also synthesized less arylphorin in vitro. However, Northern blots of total RNA from parasitized and non-parasitized, control insects showed that the arylphorin transcript level was unaffected by parasitization suggesting a biochemical block at the translational level. In vitro translation followed by immunoprecipitation of arylphorin indicated that the mRNA was present and translatable at equal levels in both parasitized and control insects. Injection of purified virus elicited the response observed in naturally parasitized larvae, demonstrating that the effect on arylphorin synthesis is mediated, either directly or indirectly, by polydnavirus gene product(s).

Glucose metabolism in an insect Manduca sexta and effects of parasitism

The metabolism of [1-13C]glucose was examined during the last larval stadium of an insect Manduca sexta (Lepidoptera: Sphingidae) parasitized by Cotesia congregata (Hymenoptera: Braconidae). Following injection, the isotopically substituted glucose was metabolized at a significantly lower rate by parasitized larvae than by normal, control insects. 13C enrichment was principally observed in [1-13C]trehalose in both groups. Randomization of the label at the triose phosphate step was evidenced by incorporation of 13C into C6 of trehalose. Parasitized and control larvae both synthesized [1,6-13C]glycogen but the relative amount of label observed in parasitized larvae was greater. The ratio of C6/C1 enrichment in trehalose and glycogen was significantly less in parasitized larvae. The rate of labelled trehalose and glycogen synthesis was relatively high when compared with the estimated rate of glycolytic glucose oxidation, and the difference in C6/C1 enrichment ratio between normal and parasitized insects was, therefore, not reflective of a difference in the rate of substrate cycling, but rather, was due to the increased synthesis of [1-13C]glycogen in parasitized larvae when compared with controls. Inhibition of glycolysis by administration of iodoacetate to normal larvae resulted in an increase in the incorporation of 13C into glycogen relative to glucose metabolized, suggesting that inhibition of glycolysis may be responsible for the higher level of glycogen synthesis observed in parasitized insects. In control larvae, significant 13C enrichment from [1-13C]glucose was observed in fat, but no evidence of lipogenesis was observed in parasitized insects. Iodoacetate had no observable effects on the relative amount of 13C incorporated into fat. Malonic acid and cyanide resulted in accumulation of 13C from [1-13C]glucose in several TCA cycle intermediates of normal larvae, but had little effect on the relative enrichments of trehalose, glycogen and fat.

Cellular immunosuppressive protein in the plasma of parasitized insect larvae

Evidence that endoparsitoid wasps may suppress the host cellular defense reaction in order to survive within the hemocoel of their host insects was obtained by isolating a cellular immunosuppressive factor from the larval plasma (hemolymph without cells) of the armyworm Pseudaletia separata parasitized with the wasp Cotesia kariyai. The purified proteinaceous factor suppresses hemocyte degranulation and subsequent immune reactions such as nodule formation and encapsulation in the armyworm larvae. The immunosuppressive protein exists not only in the plasma of parasitized larvae but also in the plasma of unparasitized larvae. However, its concentration is much less in unparasitized than in parasitized larvae. Purification procedures involved gel exclusion, ion exchange, and reversed phase high performance liquid chromatography (HPLC). Gel exclusion HPLC and SDS-polyacrylamide gel electrophoresis suggest an approximately 470-kDa hexamer composed of identical subunits of 82 kDa. Aryl amino acids such as tyrosine and phenylalanine comprise about 20% of the total protein amino acid. The sequence of 28 amino acid residues at the amino terminus of the factor was determined to be as follows: Ser-Val-Val-Pro-Thr-Lys-His-Glu-Ile-Lys-Val-Lys-Ala-Val-Glu- Pro-Gln-Tyr-Ile-Xaa-Tyr-Gln-Arg-Lys-Ile-Leu-Ala-Leu-Phe.

Expression of polydnavirus genes from the parasitoid wasp Cotesia kariyai in two noctuid hosts

DNA purified from polydnavirus particles isolated from the parasitoid wasp Cotesia kariyai contained double-stranded closed circular molecules which were polydisperse in molecular weight. 2 days after viral injection into the host armyworm larvae viral DNA was detected in all tested larval tissues, including haemocytes, fat body, nerve cord and brain. Viral transcripts were also observed in all the tissues of virus-injected larvae. The most specific tissue was haemocytes because more viral DNA and RNA was detected than in the other tissues. Viral transcripts were not detected in haemocytes of virus-injected larvae of common cutworm. The present data suggest that C. kariyai virus (CkV) gene expression occurs species-specifically, although viral DNA can be detected in all tested tissues of the habitual host armyworm.

Characterization of a novel protein associated with the parasitization of lepidopteran hosts by an endoparasitic wasp

We report basic biochemical characteristics of a parasitism-specific protein (PSP) expressed in hosts (Trichopluisa ni) of a parasitic wasp (Chelonus near curvimaculatus). Size exclusion HPLC and SDS-PAGE analysis of cross-linked products indicated the native conformation of the protein is as a monomeric polypeptide with an estimated M(r) of 185,000. Resolution by non-denaturing PAGE revealed two major PSP bands with different charges, PSP-1 and PSP-2, each of which corresponded to several isoforms on native IEF with a pl range of 4.57-5.45. Sequences for the N-terminus region and internal peptides after fragmentation of purified preparations of PSP-1 and PSP-2 did not resemble the sequence of any reported protein. Immunological characterization of PSP using antibodies generated against virus proteins from C. near curvimaculatus female wasps revealed that PSP shares a common epitope(s) with some structural components of the wasp polydnavirus.

Structure and evolutionary implications of a "cysteine-rich" Campoletis sonorensis polydnavirus gene family

For successful parasitization, the female Campoletis sonorensis endoparasitic wasp injects a polydnavirus into its host, Heliothis virescens, during oviposition. Viral gene expression induces immunosuppression and alters development of the host. We report here that three abundantly expressed genes, VHv1.1, WHv1.0, and WHv1.6, describes a polydnavirus "cysteine-rich" gene family which may be important in inducing these host manifestations. These genes have a similar primary gene structure and their proteins contain cysteine motifs characteristic of snail ion-channel ligands, the omega-conotoxins. Like the omega-conotoxins, the intercysteine amino acid residues are hypervariable with only three identical amino acids in all motifs. The conservation of this domain in the three viral genes may reflect an important functional role for these viral proteins in the parasitization of H. virescens. The three genes also contain introns similar in sequence at comparable positions in their 5' untranslated leaders and coding sequences. VHv1.1 contains two cysteine motifs, and each motif is interrupted by an intron at the same position as in the cysteine motifs of WHv1.0 and WHv1.6. Intron 2 sequences of WHv1.0 and WHv1.6 are 92% identical, while the immediately flanking exon sequences encoding the cysteine motifs are only 76% identical. This provides an example of nuclear pre-mRNA introns which are more conserved than flanking exons among members of a gene family.

Structure of a growth-blocking peptide present in parasitized insect hemolymph

Last instar larvae of the insect armyworm, Pseudaletia separata, parasitized with the parasitoid wasp, Apanteles kariyai, do not initiate metamorphosis and, ultimately, the wasp larvae emerge from the host larvae about 10 days after parasitization (Tanaka, T., Agui, N., and Hiruma, K. (1987) Gen. Comp. Endocrinol. 67, 364-374). It is necessary for the parasitoid wasp to perturb the armyworm's endocrinological processes that control normal metamorphosis from larvae to pupae. This endocrinological perturbation allows the parasitoid to complete its larval growth before emerging from the host larvae. It is obligatory for the parasitoid larvae to emerge while the host is still in a larval stage because the sclerotized pupal cuticle is impenetrable for the parasitoid larvae. A growth-blocking peptide with repressive activity against juvenile hormone esterase has been proven to exist in the parasitized host larval plasma (Hayakawa, Y. (1990) J. Biol. Chem. 265, 10813-10816). Here, I describe the detailed structure of this peptide and also the corresponding synthetic peptide to confirm this structure.

Electrophoretic characterization of chromosomal DNA from two microsporidia

Spores of two microsporidia, Nosema pyrausta (from the European corn borer, Ostrinia nubilalis) and N. furnacalis (from the Asian corn borer, O. furnacalis) were harvested from laboratory-reared O. nubilalis caterpillars and purified by centrifugation through Percoll. Conditions permitting in vitro germination were defined for both species and found to be different. N. pyrausta spores were incubated in 0.1 N KOH for 30 min, recovered by centrifugation, and resuspended in 1 ml of an equal mixture of 1% low melting point (LMP) agarose and L-15B medium at 37 degrees C to induce germination. N. furnacalis spores were first washed in 10 mM Na2EDTA in 1 mM Tris base, pH 7.5, exposed to 0.01 N KOH in 0.17 M KCl for 30 min, centrifuged, and germinated in 1 ml of an equal mixture of 1% LMP agarose and 0.17 M KCl in 10 mM Na2EDTA (pH 8), at 37 degrees C. Eighty to 90% of the spores of each species germinated. Germinated spores were pipetted into a casting mold. Before electrophoresis, agarose blocks were incubated 48 hr at 50 degrees C in 10 mM Tris base/100 mM Na2EDTA, pH 7.8, with 1 mg/ml proteinase K and 1% N-laurylsarcosine to release the chromosomal DNA from sporoplasms. After pulsed-field electrophoresis, ethidium bromide staining revealed 13 chromosomal bands ranging in size from 1390- to 440-kb pairs and 1360- to 440-kb pairs in N. pyrausta and N. furnacalis, respectively. The difference in size estimates of corresponding chromosomes in the two species was not more than 60-kb pairs.