Parasitized Host Larvae Research Articles

Shaping the Microbial Landscape: Parasitoid-Driven Modifications of Bactrocera dorsalis Microbiota

Koinobiont endoparasitoids regulate the physiology of their hosts through altering host immuno-metabolic responses, processes which function in tandem to shape the composition of the microbiota of these hosts. Here, we employed 16S rRNA and ITS amplicon sequencing to investigate whether parasitization by the parasitoid wasps, Diachasmimorpha longicaudata (Ashmaed) (Hymenoptera: Braconidae) and Psyttalia cosyrae (Wilkinson) (Hymenoptera: Braconidae), induces gut dysbiosis and differentially alter the gut microbial (bacteria and fungi) communities of an important horticultural pest, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae). We further investigated the composition of bacterial communities of adult D. longicaudata and P. cosyrae to ascertain whether the adult parasitoids and parasitized host larvae share microbial taxa through transmission. We demonstrated that parasitism by D. longicaudata induced significant gut perturbations, resulting in the colonization and increased relative abundance of pathogenic gut bacteria. Some pathogenic bacteria like Stenotrophomonas and Morganella were detected in both the guts of D. longicaudata-parasitized B. dorsalis larvae and adult D. longicaudata wasps, suggesting a horizontal transfer of microbes from the parasitoid to the host. The bacterial community of P. cosyrae adult wasps was dominated by Arsenophonus nasoniae, whereas that of D. longicaudata adults was dominated by Paucibater spp. and Pseudomonas spp. Parasitization by either parasitoid wasp was associated with an overall reduction in fungal diversity and evenness. These findings indicate that unlike P. cosyrae which is avirulent to B. dorsalis, parasitization by D. longicaudata induces shifts in the gut bacteriome of B. dorsalis larvae to a pathobiont-dominated community. This mechanism possibly enhances its virulence against the pest, further supporting its candidacy as an effective biocontrol agent of this frugivorous tephritid fruit fly pest.

Parasitoid-induced changes in metabolic rate and feeding activity of the emerald ash borer (Coleoptera: Buprestidae): implications for biological control

Parasitoid-host interactions form the foundation of biological control strategies against many agriculture and forest insect pests. The emerald ash borer (EAB), Agrilus planipennis (Coleoptera: Buprestidae), is a serious invasive pest of ash (Fraxinus spp.) trees in North America. Tetrastichus planipennisi (Hymenoptera: Eulophidae) is a gregarious, koinobiont endoparasitoid, attacking late (3rd to 4th) instars of EAB larvae, which feed in the live phloem of ash trunks or branches, making serpentine-like galleries filled with larval frass. In the present study, we tested the hypothesis that T. planipennisi regulates the host metabolism and feeding activity to optimize its offspring development and fitness. We first compared the respiration rate of parasitized and unparasitized host larvae at different times after parasitism, and then measured feeding activity of both parasitized and unparasitized host larvae inside their feeding galleries. Although parasitized host larvae increased metabolic rate and feeding activity in the first few days of parasitism, T. planipennisi parasitism induced an overall reduction of the metabolic rate and decrease in feeding activity of parasitized host larvae over their development period. In addition, there was a negative relationship between feeding activity of parasitized hosts and brood sizes of the parasitoid progeny—i.e., the more parasitoid progeny a host larva received, the less feeding activity the host had. These findings suggest that T. planipennisi has limited ability to optimize its offspring development and fitness through regulations of the host metabolism and feeding activity and its parasitism reduces feeding damage of parasitized EAB larvae to infested ash trees.

Host trehalose metabolism disruption by validamycin A results in reduced fitness of parasitoid offspring

The general cutworm, Spodoptera litura (Lepidoptera: Noctuidae) is a worldwide destructive omnivorous pest and the endoparasitoid wasp Meteorus pulchricornis (Hymenoptera: Braconidae) is the dominant endoparasitoid of S. litura larvae. Trehalase is a key enzyme in insect trehalose metabolism and plays an important role in the growth and development of insects. However, the specific function of trehalase in parasitoid and host associations has been less reported. In this study, we obtained two trehalase genes (SlTre1 and SlTre2) from our previously constructed S. litura transcriptome database; they were highly expressed in 3rd instar larvae. SlTre1 was mainly expressed in the midgut, and SlTre2 was expressed highest in the head. SlTre1 and SlTre2 were highly expressed 5 days after parasitization by M. pulchricornis. Treatment with the trehalase inhibitor validamycin A significantly inhibited the expression levels of SlTre1 and SlTre2, and the trehalase activity. Besides, the content of trehalose was increased but the content of glucose was decreased 24 h after validamycin A treatment in parasitized S. litura larvae. In addition, the immune-related genes in phenoloxidase (PO) pathway and fatty acid synthesis-related genes in lipid metabolism were upregulated in parasitized host larvae after validamycin A treatment. Importantly, the emergence rate, proportion of normal adults, and body size of parasitoid offspring was decreased in parasitized S. litura larvae after validamycin A treatment, indicating that validamycin A disrupts the trehalose metabolism of parasitized host and thus reduces the fitness of parasitoid offspring. The present study provides a novel perspective for coordinating the application of biocontrol and antibiotics in agroecosystem.

Kairomone-induced changes in foraging activity of the larval ectoparasitoid Holepyris sylvanidis are linked with an increased number of male parasitoid offspring

Interactions between stored product pest insects and their parasitoids are well known to be mediated by infochemicals. However, little knowledge is available about the extent to which parasitoid responses to host kairomones improve host search and parasitization success. Here, we tested whether the release of host-specific kairomones of the confused flour beetle, Tribolium confusum, improves host finding of the larval ectoparasitoid Holepyris sylvanidis. Previous studies revealed that volatiles from host larval feces [i.e., (E)-2-nonenal and 1-pentadecene] attract the parasitoid. To determine the most attractive concentration of these two key components, we conduced Y-tube olfactometer bioassays. Most female parasitoids were attracted to a mixture of (E)-2-nonenal and 1-pentadecene at the lowest concentration, while the highest concentration was repellent. Volatiles from host adults (methyl-p-benzoquinone and 4,8-dimethyldecanal) did not attract the parasitoid females at any of the concentrations tested. In flight cage experiments, we analyzed the host finding success of H. sylvanidis by offering host larvae in a Petri dish for 3 days (i) with additionally applied host larval kairomones in the most attractive concentration (test) or (ii) without additional kairomones (control). In test cages, the parasitoids removed a significantly higher number of paralyzed host larvae from the initial population within 48 h than in control cages. After 72 h, significantly more host larvae were parasitized in test cages than in the control. The offspring of parasitoids in test cages differed from the one in control cages by total numbers and especially the number of males. Significantly more parasitoids emerged from the parasitized host larvae in test cages, with enhanced male offspring. Our study demonstrates that the parasitoid’s response to host-associated volatiles can improve parasitization success but also affects the number of males in the parasitoids’ progeny.

Seasonal abundance of Cotesia ruficrus (Hymenoptera: Braconidae) and its host tea looper, Hyposidra talaca (Lepidoptera: Geometridae) in tea ecosystem

Investigations were undertaken for a better understanding of seasonality, interaction with tea ecosystem, and parasitic impact of an endoparasitoid Cotesia ruficrus (Haliday) (Hymenoptera: Braconidae) on the destructive tea looper Hyposidra talaca (Walker) (Lepidoptera: Geometridae). The population abundance of C. ruficrus was noticed as high in the months of pre-winter and spring seasons which was coincided with the population increase of H. talaca. C. ruficrus found to foraging and collecting nectar from the flowers of Lantana camera L., Moringa oleifera Lam., and Clerodendron infortunatum L. associated with the tea ecosystem. The life table parameters including intrinsic rate of natural increase (rm ) and net reproductive rate (Ro) of C. ruficrus were 0.203 per day and 41.11 female offspring/female, respectively, with the gross reproductive rate (∑mx) 50.09 eggs/female. The parasitic impact of C. ruficrus has significantly affected the food consumption and development of H. talaca. Resultantly, a drastic reduction in body weight, changes in differential hemocyte count (DHC), and morphology of hemocytes were observed in parasitized host larvae. Toxic effect of quinalphos and thiamethoxam on C. ruficrus showed 100% mortality followed by bifenthrin > deltamethrin > emamectin benzoate > flubendiamide > fenpyroxymate after 72 h of the application.

Symbiotic bracovirus of a parasite manipulates host lipid metabolism via tachykinin signaling.

Parasites alter host energy homeostasis for their own development, but the mechanisms underlying this phenomenon remain largely unknown. Here, we show that Cotesia vestalis, an endoparasitic wasp of Plutella xylostella larvae, stimulates a reduction of host lipid levels. This process requires excess secretion of P. xylostella tachykinin (PxTK) peptides from enteroendocrine cells (EEs) in the midgut of the parasitized host larvae. We found that parasitization upregulates PxTK signaling to suppress lipogenesis in midgut enterocytes (ECs) in a non-cell-autonomous manner, and the reduced host lipid level benefits the development of wasp offspring and their subsequent parasitic ability. We further found that a C. vestalis bracovirus (CvBV) gene, CvBV 9–2, is responsible for PxTK induction, which in turn reduces the systemic lipid level of the host. Taken together, these findings illustrate a novel mechanism for parasite manipulation of host energy homeostasis by a symbiotic bracovirus gene to promote the development and increase the parasitic efficiency of an agriculturally important wasp species.

CLP gene family, a new gene family of Cotesia vestalis bracovirus inhibits melanization of Plutella xylostella hemolymph.

Polydnaviruses (PDVs) are obligatory symbionts of parasitoid wasps and play an important role in suppressing host immune defenses. Although PDV genes that inhibit host melanization are known in Microplitis bracovirus, the functional homologs in Cotesia bracoviruses remain unknown. Here, we find that Cotesia vestalis bracovirus (CvBV) can inhibit hemolymph melanization of its host, Plutella xylostella larvae, during the early stages of parasitization, and that overexpression of highly expressed CvBV genes reduced host phenoloxidase activity. Furthermore, CvBV-7-1 in particular reduced host phenoloxidase activity within 12 h, and the injection of anti-CvBV-7-1 antibody increased the melanization of parasitized host larvae. Further analyses showed that CvBV-7-1 and three homologs from other Cotesia bracoviruses possessed a C-terminal leucine/isoleucine-rich region and had a similar function in inhibiting melanization. Therefore, a new family of bracovirus genes was proposed and named as C-terminal Leucine/isoleucine-rich Protein (CLP). Ectopic expression of CvBV-7-1 in Drosophila hemocytes increased susceptibility to bacterial repression of melanization and reduced the melanotic encapsulation of parasitized D. melanogaster by the parasitoid Leptopilina boulardi. The formation rate of wasp pupae and the eclosion rate of C. vestalis were affected when the function of CvBV-7-1 was blocked. Our findings suggest that CLP genes from Cotesia bracoviruses encoded proteins that contain a C-terminal leucine/isoleucine-rich region and function as melanization inhibitors during the early stage of parasitization, which is important for successful parasitization.

Effect of Temperature on the Immature Developmental Time and Adult Longevity of Apanteles Galleriae Wilkinson (Hym. Braconidae)

The greaterwax moth, Galleria mellonella (L.), is a known pest of the Egyptian and worldwide beekeeping. The solitary endoparasitoid, Apanteles galleriae Wilkinson is one of important natural enemies of the pest. The study aimed to determine the effect of temperatures under near-continuous darkness on the immature developmental time, growth of parasitized larvae and adult longevity of A. galleriae. The duration of developmental period of male was less than that of female irrespective of temperatures. At 20°C temperature and 75% RH, the duration ranged from 21.7 days for males and 23.8 days for females, decreased to 18.1 and 19.2 days at 25°C,17.1 and 18.1 days at 27°C and 16.0 and 17.3 days at 30°C, respectively. Parasitism by A. galleriae retards the growth of G. mellonella larvae. The initial weight of wax moth larva at the time of parasitization was 3.5±0.2 mg and was significantly lower (9.9±0.7 mg) prior to parasitoid egression than that of the non-parasitized larva (89.5±5.2 mg). The parasitized host larvae eventually weighed up to 70 to 88% less than the non-parasitized larvae. The adults survived starvation, water- or one -day honey feeding for few days, while they lived for significantly longer periods when they provided daily with pure honey. Longevity of females fed on pure honey was significantly longer than males at all tested temperatures. The results may be of value for developing mass rearing techniques and biological control of wax moths by A. galleriae.

Effects of temperature on the activity of antioxidant enzymes in larvae of Bactrocera dorsalis (Diptera: Tephritidae) parasitized by Diachasmimorpha longicaudata (Hymenoptera: Braconidae): Optimizing the mass rearing of this braconid by varying the temperature

Diachasmimorpha longicaudata is the most widely used endoparasitoid in biocontrol programmes against various species of tephritids and is continuously mass-reared under laboratory conditions at a constant temperature; however, little is known about how varying the temperature might affect the effectiveness of the mass rearing of immature D. longicaudata. This study aimed to determine the optimum temperature for the development of larvae D. longicaudata the larvae of its host, Bactrocera dorsalis. Third-instar B. dorsalis were exposed for 4 h to five pairs of parasitoids, and then they were kept at one of six temperatures ranging from 19°C to 34°C. The activities of three major antioxidant enzymes (CAT, POX, SOD) were individually measured 4, 24, 48 and 72 h after exposure to each of the six temperatures. The results were as follows: for CAT the highest CAT activities were recorded at 25°C (intervals 5-24 h and 25-48 h), at 28°C (interval 0-4 h) and at 31°C (interval 49-72 h), and for POX and SOD identically at 25°C (intervals 0-4 h, 5-24 h) and at 31°C (intervals 25-48 h, 49-72 h), respectively. Subsequently, the effects keeping the parasitized larvae at these different temperatures on the biological attributes of D. longicaudata reared under laboratory conditions were investigated. The percentage of their eggs that hatched, percentage of adults that emerged, pupal weight and longevity were significantly greater than that recorded for the control when the parasitized host larvae were kept at 28°C for 4 h, 25°C for 5 and 48 h and 31°C for 49 and 72 h.

Oviposition strategy for superparasitism in the gregarious parasitoid Oomyzus sokolowskii (Hymenoptera: Eulophidae).

Superparasitism is an adaptive strategy in solitary parasitoids, yet insufficient evidence confirms this in gregarious ones. We here ask whether the gregarious parasitoid Oomyzus sokolowskii is able to discriminate in attack and progeny allocation between parasitized and unparasitized Plutella xylostella larvae, and how the parasitoid allocates brood size and sex to superparasitized hosts due to some circumstances. We found that female parasitoids preferred unparasitized to parasitized host larvae, and allocated a smaller brood with more males in the later than in the former host. Brood size and sex ratio decreased from superparasitized hosts with a 48 h interval since a previous attack compared with one without an interval; they also declined from the host superparasitized by the parasitoid with oviposition experience compared with one without it. Brood size and sex ratio did not differ between the host superparasitized by the same parasitoid as in the first attack and that by a different one. Our findings suggest that O. sokolowskii females may adjust their oviposition decisions on progeny allocation in response to parasitized P. xylostella larvae to maximize their fitness gains from superparasitism.

Effects of Storage at Suboptimal Temperatures on the In Vitro-Reared Parasitoid Exorista larvarum (Diptera: Tachinidae).

Exorista larvarum (L.) is a tachinid parasitoid native to the Palearctic region, known as an antagonist of lepidopterous defoliators. This species is suitable to be cultured in vitro, and yields of fecund adults, approaching those usually attained in host larvae, have been previously achieved on artificial media. Direct oviposition by E. larvarum on media has not yet been obtained, and the eggs for the in vitro rearing are routinely removed from parasitized host larvae. However, many eggs are usually laid throughout the cage by captive females and can be retrieved by placing them on artificial media. Storage at low temperatures provides a method for prolonging the development of insects and stockpile them when not needed immediately. We studied the effects of storage at 20 °C (for 5 d or until pupation) or 15 °C (for 5 d or until egg hatching) on the in vitro development of E. larvarum. Lower temperatures were excluded, because previous studies showed a strong negative impact on hatching when the eggs were stored at 5 °C or 10 °C. For the experiments, eggs were removed from hosts and placed on an artificial medium. The results suggested that it is possible to delay the development of the in vitro-reared E. larvarum, which eventually reached the adult stage, although some negative effects on fly quality (i.e., longevity and fecundity) were also observed. Because quality is not an absolute concept, all the situations tested in this study could be appropriate according to the current requirements.

Intra- and interspecific competition in two congeneric parasitoids of the diamondback moth

In solitary parasitoids, a host can only support the complete development of a single parasitoid. For this reason, intraspecific or interspecific competition takes place whenever two or more individuals of the same or different species parasitize the same host. The exotic Diadegma semiclausum (Hellen) (Hymenoptera: Ichneumonidae) was introduced into Kenya in 2002 for the control of the diamondback moth, Plutella xylostella L. (Lepidoptera: Plutellidae), and led to the competitive displacement of its indigenous congeneric species Diadegma mollipla (Holmgren) in some areas but not in others. In an attempt to understand this process, superparasitism in D. mollipla and multiparasitism involving both species were investigated in the laboratory through exposure of non-parasitized and parasitized host larvae to D. mollipla. Hosts were exposed to the two congeners both simultaneously and sequentially. The study revealed that D. mollipla minimizes parasitism and superparasitism in the presence of hosts containing a larva of a conspecific female. When the two parasitoid species competed for non-parasitized hosts simultaneously, there were no significant differences in the total progeny produced under intraspecific vs. interspecific competition. Under simultaneous interspecific competition, D. semiclausum produced 74% of total progeny. Under sequential exposure, the species that attacked first always dominated with 85–96% of the resultant progeny, irrespective of the exposure interval. Offspring sex ratio was significantly more female-biased when the larvae were exposed to D. mollipla first. Overall, our results indicate that D. semiclausum dominates under simultaneous competition and D. mollipla dominates in terms of female progeny, but under delayed exposure to the other species, the first attacker is always the winner. On the basis of our results, D. semiclausum may not completely displace D. mollipla from diamondback moth in the field.

VENOM FROM THE ECTOPARASITIC WASP Habrobracon hebetor ACTIVATES CALCIUM-DEPENDENT DEGRADATION OF Galleria mellonella LARVAL HEMOCYTES.

Ectoparasitoids inject venom into hemolymph during oviposition. We determined the influence of envenomation by the parasitoid, Habrobracon hebetor, on the hemocytes of its larval host, Galleria mellonella. An increase in both intracellular Са(2+) content and phospholipase C activity of the host hemocytes was recorded during 2 days following envenomation by the parasitoid. The decreased hemocyte viability was detected 1, 2, and 24 h after the envenomation. Injecting of the crude venom (final protein concentration 3 μg/ml) into the G. mellonella larvae led to the reduced hemocyte adhesion. The larval envenomation caused a decrease in transmembrane potential of the hemocytes. These findings document the suppression of hemocytic immune effectors in the parasitized host larvae.

The performance of Oomyzus sokolowskii (Hymenoptera: Eulophidae) parasitizing Plutella xylostella (Lepidoptera: Plutellidae) on different host plants

Oomyzus sokolowskii Kurdjumov is a larval endoparasitoid of the diamondback moth, Plutella xylostella L., which is one of the most destructive pests of cruciferous vegetables worldwide. The performance of O. sokolowskii parasitizing P. xylostella on cauliflower (Brassica oleracea var. botrytis), Chinese cabbage (Brassica pekinensis), pakchoi (Brassica chinensis), cabbage (Brassica oleracea var. capitata), and broccoli (Brassica oleracea var. italica) was determined under laboratory conditions. Our results showed that O. sokolowskii performed best on cauliflower compared with the others, with the greatest net reproductive rate (R o = 34.99), intrinsic rate of increase (r m = 0.196), offspring emerged/host larva (9.0), percentage of parasitized host larvae with adults emerged (67.6 %), adults produced (43.6/female), and the shortest developmental time from egg to adult (15.8 days). Chinese cabbage-, pakchoi-, cabbage-, and cauliflower-adapted O. sokolowskii performed the best in percentage of parasitized host larvae with adults emerged, offspring adults produced per female, and offspring produced per host larva when parasitizing fourth instar P. xylostella larvae on cauliflower. The percentage of host-adapted female O. sokolowskii parasitizing different host-adapted fourth instar P. xylostella larvae was similar. Based on our results, we suggest that O. sokolowskii had performed best on cauliflower, which might be the best host plant to rear O. sokolowskii.

Estimating effect of augmentative biological control on grain yields from individual pearl millet heads

AbstractPearl millet is the principal staple food crop in large portions of Western Sub‐Sahelian Africa and the millet head miner (Heliocheilus albipunctella) is one of its most devastating insect pests. Since 2006, augmentative mass releases of the larval ectoparasitoid, Habrobracon hebetor, have been conducted in Mali, Burkina Faso and Niger as part of minimizing pearl millet grain losses imposed by millet head miners. These ongoing mass releases are based on low‐cost mass‐rearing of both host larvae and parasitoids. A release of parasitoids consists of placing jute bags containing pearl millet grain and flour and parasitized host larvae near pearl millet fields. The total production costs of a single jute bag with parasitized rice moth larvae are US$ 3–4. Based on a study of 6634 individual pearl millet heads collected at harvest in 12 farmers' fields in southern Niger in 2010, we demonstrated (i) a strong negative correlation between pearl millet head damage (mining) and grain yield and (ii) that parasitism by H. hebetor reduced grain losses by, on average, 34% (comparison of infested millet heads with/without parasitism) within the given growing season. Additional benefits may include reduction in millet head miners in subsequent generations. Data from 900 pearl millet heads collected in nine farmers' fields in 2011 were used to confirm data trends observed in the 2010 data and to characterize the dispersal of parasitoids in upwind and downwind directions from a release site. This study provided a quantitative description of the negative impact of millet head miner infestations on pearl millet grain yields and of benefits on grain yield of parasitism by H. hebetor. Our findings strongly support (i) intensification of mass‐rearing of H. hebetor, (ii) expansion of educational activities to increase local empowerment and understanding of the potential of augmentative biological control and (iii) optimization of H. hebetor mass release programmes among smallholders in Sub‐Sahelian Africa.

Influence of the herbivore host’s wild food plants on parasitism, survival and development of the parasitoid Diadegma insulare

Uncultivated feral host plants of insect pests often serve as reservoirs of the herbivores during temporal periods when crops are not grown, and as a consequence, understanding responses of herbivore biocontrol agents to these hosts is important when formulating strategies for pest management. Sinapis arvensis L., Erysimum cheiranthoides L. and Capsella bursa-pastoris (L.) Medicus are among the most common brassicaceous weeds in crucifer-growing areas worldwide, and can serve as hosts for the diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae). We evaluated the cascading effects of these weeds on fitness of the parasitoid Diadegma insulare (Cresson) (Hymenoptera: Ichneumonidae) reared on host larvae of P. xylostella that consumed weed leaves. Percentage parasitism of host larvae by D. insulare was highest on S. arvensis and lowest on C. bursa-pastoris in both the free-choice and no-choice situations. Values of several fitness correlates for D. insulare differed when parasitized host larvae fed on different weed species. Egg to adult development was fastest on S. arvensis and slowest on C. bursa-pastoris. Relative growth rates of pupae and adults were highest on S. arvensis whereas relative consumption rates were highest on E. cheiranthoides. Female wasps reared on hosts that consumed S. arvensis and E. cheiranthoides lived longer in the absence of food than those reared on C. bursa-pastoris. Potential impacts of these wild brassicaceous species on D. insulare populations and their role in pest management are discussed.

稻纵卷叶螟绒茧蜂对寄主的搜索行为

稻纵卷叶螟绒茧蜂是稻纵卷叶螟幼虫的重要天敌。以Y形嗅觉仪测定了稻纵卷叶螟2-3龄幼虫虫粪、4-5龄幼虫虫粪、健康水稻、稻纵卷叶螟幼虫为害后水稻在纵卷叶螟绒茧蜂对寄主的搜索过程中的作用。结果表明已交配的雌蜂显著趋向稻纵卷叶螟2-3龄幼虫虫粪和4-5龄幼虫虫粪,不趋向健康水稻、稻纵卷叶螟幼虫为害后的水稻。雄蜂、处女雌蜂不显著趋向健康水稻、稻纵卷叶螟幼虫为害后水稻、稻纵卷叶螟2-3龄幼虫虫粪、稻纵卷叶螟4-5龄幼虫虫粪。利用固相微萃取(SPME)及气相色谱/质谱(GC/MS)联用分析稻纵卷叶螟2-3龄幼虫虫粪的化学成分,并通过Y-形嗅觉仪测试已交配雌蜂对稻纵卷叶螟2-3龄幼虫虫粪化学成分标准品的嗅觉反应,结果表明已交配的雌蜂显著趋向1-十一烯和异缬草醛,稻纵卷叶螟幼虫虫粪中的1-十一烯和异缬草醛可能是稻纵卷叶螟绒茧蜂搜索寄主的利他素。;<em>Apanteles cypris</em> Nixon is one of the most important natural enemies of the larvae of rice leaf folder, <em>Cnaphalocrocis medinalis</em> Guenée. Through parasitizing their larvae, <em>A. cypris</em> wasps play a major role in biological control of <em>C</em>.<em> medinalis</em>; parasitized host larvae consume less rice leaf than non-parasitized counterparts, thus causing less damage. Previous studies suggest that some parasitoids using chemical cues to locate their hosts. In a tritrophic interaction system consisting of plants, herbivores, and their parasitoids, chemicals released from plants after herbivory are known to help many female parasitoids find their hosts efficiently. Chemical information associated with herbivory can act as an indirect defense for the plant by attracting natural enemies of the host herbivores. There are several potential sources of infochemicals used by parasitoids: the host plant, direct or indirect cues from the host. This study aims to determine if the host searching behavior of <em>A</em>. <em>cypris</em> is affected by volatiles from <em>C</em>.<em> medinalis</em>-infested and uninfested rice plants and frass produced by larvae of <em>C</em>. <em>medinalis</em>. We found that mated female <em>A</em>. <em>cypris</em> were attracted by the frass of 2nd/3rd or 4th/5th instar <em>C</em>. <em>medinalis</em> larvae but not by <em>C</em>. <em>medinalis-</em>infested and uninfested rice plants. In contrast, male and virgin female <em>A</em>. <em>cypris</em> did not respond significantly to any of the stimuli. These results indicate that the mating status of <em>A</em>. <em>cypris</em> females clearly influences their host-searching behavior in response to herbivory-associated chemical information, and we suggest that female parasitoids forage for hosts depending on their own physiological condition in a tritrophic system. To elucidate which chemicals are used by <em>A. cypris</em> to locate their hosts, we analyzed the chemical composition of frass produced by 2nd/3rd instar <em>C</em>.<em> medinalis</em> larvae using solid-phase micro-extraction (SPME) combined with gas chromatography/mass spectrometry (GC/MS). We collected 23 volatiles from the frass, including terpenoids, alcohols, ketones, amines, aldehyde. Chemical standards of the determined frass components are then tested for the chemotactic effect on mated female <em>A</em>. <em>cypris</em> using Y-tube olfactometer. We found that mated female <em>A</em>. <em>cypris</em> were significantly attracted by 1-undecene and 3-methylbutanal, and suggest that these compounds in the frass of <em>C</em>.<em> medinalis</em> larvae are the kairomones that attract endoparasitoid <em>A</em>. <em>cypris</em>. Our results may prove to be helpful for the agricultural industry through use of these kairomones as control agents for <em>C</em>. <em>medinalis</em>, and are the basis of further study into the tritrophic system of rice -<em>C</em>. <em>medinalis</em>-<em>A. cypris</em> and development of new control methods.

Effects of the mixed biocide Bacillus thuringiensis-abamectin on the development of the parasitoid Microplitis mediator and its host Helicoverpa armigera

The effects of the mixed biocide Bacillus thuringiensis Berliner with abamectin (BtA) on the development of the parasitoid Microplitis mediator (Haliday) (Hymenoptera: Braconidae) and its cotton bollworm host, Helicoverpa armigera (Hubner) (Lepidoptera: Noctuidae), were evaluated in the laboratory. Weight gain in larvae of H. armigera was initially delayed, but larval developmental period increased and pupal weight increased when they were fed on a diet containing BtA. Due to increased longevity of the host larvae, the susceptible period to parasitization of H. armigera by M. mediator increased when the host larvae were reared on diets containing BtA at concentrations of 0.5, 1, 2, and 4 μg g -1 . The longevity of female and male parasitoids significantly decreased when newly emerged wasps were fed a honey solution containing 200 μg ml -1 BtA in comparison with those fed only a honey solution. Mean longevity was significantly prolonged when parasitoids were fed a honey solution and BtA-honey solution in comparison with those fed BtA-distilled water, distilled water, or nothing. There were no significant differences compared with the control in any biological characteristics for the offspring of female parasitoids fed the honey solutions containing BtA at concentrations of 50, 100, and 200 μg ml -1 ; characteristics measured include the egg-larval period, pupal weight, male and female pupal periods, adult fresh weight, and adult longevity. When female parasitoids parasitized host larvae that had been fed the diet containing BtA, their male and female pupal periods were significantly prolonged compared with the control (without BtA).

Compatibility of Heterorhabditis indica (Rhabditida: Heterorhabditidae) and Habrobracon hebetor (Hymenoptera: Braconidae) for biological control of Plodia interpunctella (Lepidoptera: Pyralidae)

The potential for integrating the application of Heterorhabditis indica Poinar, Karunakar, and David (Homl strain) and release of Habrobracon hebetor (Say) in the management of the Indianmeal moth, Plodia interpunctella (Hübner), was investigated in the laboratory. A combination of the nematode and the parasitoid was observed to increase the mortality of P. interpunctella. The interaction between the nematodes and parasitoids was not antagonistic but could possibly be additive or synergistic. Release of parasitoids or application of nematodes alone generated between 62.25% and 71.25% mortality of the P. interpunctella larvae whereas combination of the two resulted in 98.0–99.25% mortality. The nematode was found to be virulent to the larvae of the parasitoid but not to the pupae and the adults. Adult female parasitoids that were exposed to both uninfected and nematode-infected P. interpunctella larvae in a free-choice arena were unable to distinguish between the two. In contrast, infective juvenile nematodes preferentially infected parasitized host larvae compared with healthy non-parasitized host larvae. Nematode reproduction was not significantly different in parasitized and non-parasitized host larvae. The combined application of H. indica and H. hebetor for the control of P. interpunctella may be beneficial if the detrimental effects of the nematode on the parasitoid can be minimized through optimum timing.

The effects of parasitism by the ectoparasitoid Bracon hebetor Say (Hymenoptera: Braconidae) on host hemolymph proteins in the Mediterranean flour moth Ephestia kuehniella Zeller (Lepidoptera: Pyralidae)

Parasitism of lepidopteran larvae by braconid wasps has significant effects on host hemolymph proteins and the physiology of the host insect. In this study the post-parasitism effects of a gregarious idiobiont ectoparasitoid (Bracon hebetor) on hemolymph plasma proteins in the final instar larvae of the host (Ephestia kuehniella) were investigated. Hemolymph plasma proteins were analyzed using spectrophotometry and sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). Total quantity of plasma proteins in the host's hemolymph decreased slightly 24 and 48 h after parasitization; however, SDS-PAGE analysis showed that the quantity of 12 proteins decreased, whereas that of 5 proteins increased in concentration in the hemolymph of parasitized host larvae 24 and 48 h post-parasitism. Therefore, we conclude that host regulation of E. kuehniella by B. hebetor involves only quantitative changes in host plasma proteins and does not lead to upregulation of novel proteins.