Bt rice does not disrupt the host-searching behavior of the parasitoid Cotesia chilonis.
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ABSTRACT:
SUBMITTER: Liu Q
PROVIDER: S-EPMC4606804 | biostudies-other | 2015 Oct
REPOSITORIES: biostudies-other
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Project description:The parasitoid wasp Ampulex compressa envenomates the brain of its host the American cockroach (Periplaneta americana), thereby making it a behaviorally compliant food supply for its offspring. The target of venom injection is a locomotory command center in the brain called the central complex. In this study, we investigate why stung cockroaches do not respond to injuries incurred during the manipulation process by the wasp. In particular, we examine how envenomation compromises nociceptive signaling pathways in the host. Noxious stimuli applied to the cuticle of stung cockroaches fail to evoke escape responses, even though nociceptive interneurons projecting to the brain respond normally. Hence, while nociceptive signals are carried forward to the brain, they fail to trigger robust nocifensive behavior. Electrophysiological recordings from the central complex of stung animals demonstrate decreases in peak firing rate, total firing, and duration of noxious-evoked activity. The single parameter best correlated with altered noxious-evoked behavioral responses of stung cockroaches is reduced duration of the evoked response in the central complex. Our findings demonstrate how the reproductive strategy of a parasitoid wasp is served by venom-mediated elimination of aversive, nocifensive behavior in its host.
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Project description:Vitellogenin receptor (VgR) is essential to vitellogenin uptaking and dominates ovary maturation in insects. However, the function of VgR in parasitoid wasps is largely unknown. Here, we applied the Drosophila parasitoid Leptopilina boulardi as a study model to investigate the function of VgR in parasitoids. Despite the conserved sequence characteristics with other insect VgRs, we found L. boulardi VgR (LbVgR) gene was highly expressed in head but lower in ovary. In addition, we found that LbVgR had no effects on ovary development, but participated in host-searching behavior of female L. boulardi and mating behavior of male L. boulardi. Comparative transcriptome analysis further revealed LbVgR might play crucial roles in regulating the expression of some important chemoreception genes to adjust the parasitoid behaviors. These results will broaden our knowledge of the function of VgR in insects, and contribute to develop advanced pest management strategies using parasitoids as biocontrol agents.
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Project description:Neonicotinoids are widely used insecticides, but their use is subject of debate because of their detrimental effects on pollinators. Little is known about the effect of neonicotinoids on other beneficial insects such as parasitoid wasps, which serve as natural enemies and are crucial for ecosystem functioning. Here we show that sublethal doses of the neonicotinoid imidacloprid impair sexual communication and host finding in the parasitoid wasp Nasonia vitripennis. Depending on the dose, treated females were less responsive to the male sex pheromone or unable to use it as a cue at all. Courtship behaviour of treated couples was also impeded resulting in a reduction of mating rates by up to 80%. Moreover, treated females were no longer able to locate hosts by using olfactory cues. Olfaction is crucial for the reproductive success of parasitoid wasps. Hence, sublethal doses of neonicotinoids might compromise the function of parasitoid wasps as natural enemies with potentially dire consequences for ecosystem services.
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Project description:BackgroundTransgenic Bt rice line T2A-1 expresses a synthesized cry2A gene that shows high resistance to Lepidoptera pests, including Cnaphalocrocis medinalis (Guenée) (Lepidoptera: Pyralidae). Plant volatile orientation cues and the physical characteristics of the leaf surface play key roles in host location or host-plant acceptance of phytophagous insects. These volatile compounds and physical traits may become altered in Bt rice and it is not known whether this influences the behavior of C. medinalis when searching for oviposition sites.ResultsThe results of electronic nose analysis showed that the Radar map of Bt rice cultivars was analogous to the non- Bt rice cultivars at each growing stage. PCA analysis was able to partly discriminate between some of the Bt vs. non-Bt rice sensors, but could not to separate Bt cultivars from non-Bt cultivars. The total ion chromatogram between Bt and non-Bt rice cultivars at the seedling, booting and tillering stages were similar and 25 main compounds were identified by GC-MS. For most compounds, there was no significant difference in compound quantities between Bt and non-Bt rice cultivars at equivalent growth stages. The densities of the tubercle papicles and the trichomes on the upper and lower surfaces were statistically equal in Bt and non-Bt rice. The target pest, C. medinalis, was attracted to host rice plants, but it could not distinguish between the transgenic and the isogenic rice lines.ConclusionsThere were no significant differences between the Bt rice line, T2A-1 and the non-Bt rice for volatiles produced or in its physical characteristics and there were no negative impacts on C. medinalis oviposition behavior. These results add to the mounting evidence that Bt rice has no negative impact on the target insect oviposition behavior.
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Project description:The area planted with insect-resistant genetically engineered crops expressing Bacillus thuringiensis (Bt) genes has greatly increased in many areas of the world. Given the nearby presence of non-Bt crops (including those planted as refuges) and non-crop habitats, pests targeted by the Bt trait have a choice between Bt and non-Bt crops or weeds, and their host preference may greatly affect insect management and management of pest resistance to Bt proteins. In this study, we examined the oviposition preference of the target pest of Bt rice, Chilo suppressalis, for Bt versus non-Bt rice plants as influenced by previous damage caused by C. suppressalis larvae. The results showed that C. suppressalis females had no oviposition preference for undamaged Bt or non-Bt plants but were repelled by conspecific-damaged plants whether Bt or non-Bt Consequently, C. suppressalis egg masses were more numerous on Bt plants than on neighbouring non-Bt plants both in greenhouse and in field experiments due to the significantly greater caterpillar damage on non-Bt plants. We also found evidence of poorer performance of C. suppressalis larvae on conspecific-damaged rice plants when compared with undamaged plants. GC-MS analyses showed that larval damage induced the release of volatiles that repelled mated C. suppressalis females in wind tunnel experiments. These findings suggest that Bt rice could act as a dead-end trap crop for C. suppressalis and thereby protect adjacent non-Bt rice plants. The results also indicate that the oviposition behaviour of target pest females should be considered in the development of Bt resistance management strategies.
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Project description:BackgroundDiachasmimorpha longicaudata is a hymenopteran fruit fly endoparasitoid. Females of this species find their hosts for oviposition by using complex sensorial mechanisms in response to physical and chemical stimuli associated with the host and host habitat. Ecological and behavioral aspects related to host-seeking behavior for oviposition have been extensively studied in D. longicaudata, including the identification of volatile organic compounds acting as attractants to females. In this sense, molecular mechanisms of chemoreception have been explored in this species, including a preliminary characterization of odorant-binding proteins (OBPs), chemosensory proteins (CSPs) and odorant receptors (ORs), among other proteins. Functional assays on OBP and CSP have been conducted as a first approach to identify molecular mechanisms associated with the female host-seeking behavior for oviposition. The aims of the present study were to identify the D. longicaudata sensory gene repertoire expressed in the antenna of sexually mature and mated individuals of both sexes, and subsequently, characterize transcripts differentially expressed in the antennae of females to identify candidate genes associated with the female host-seeking behavior for oviposition.ResultsA total of 33,745 predicted protein-coding sequences were obtained from a de novo antennal transcriptome assembly. Ten sensory-related gene families were annotated as follows: 222 ORs, 44 ionotropic receptors (IRs), 25 gustatory receptors (GRs), 9 CSPs, 13 OBPs, 2 ammonium transporters (AMTs), 8 pickpocket (PPKs) receptors, 16 transient receptor potential (TRP) channels, 12 CD36/SNMPs and 3 Niemann-Pick type C2 like proteins (NPC2-like). The differential expression analysis revealed 237 and 151 transcripts up- and downregulated, respectively, between the female and male antennae. Ninety-seven differentially expressed transcripts corresponded to sensory-related genes including 88 transcripts being upregulated (87 ORs and one TRP) and nine downregulated (six ORs, two CSPs and one OBP) in females compared to males.ConclusionsThe sensory gene repertoire of D. longicaudata was similar to that of other taxonomically related parasitoid wasps. We identified a high number of ORs upregulated in the female antenna. These results may indicate that this gene family has a central role in the chemoreception of sexually mature females during the search for hosts and host habitats for reproductive purposes.
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Project description:Host plants, pathogens and their herbivore vectors systems have complex relationships via direct and indirect interactions. Although there are substantial gaps in understanding these systems, the dynamics of the relationships may influence the processes of virus transmission and plant disease epidemics. Rice dwarf virus (RDV) is mainly vectored by green rice leafhoppers (GRLHs), Nephotettix cincticeps (Uhler) (Hemiptera: Cicadellidae) in a persistently circulative manner. In this study, host plant selection preferences of non-viruliferous and viruliferous (carrying RDV) GRLHs between RDV-free and RDV-infected plants were tested. Non-viruliferous GRLHs preferred RDV-infected rice plants over RDV-free rice plants, and viruliferous GRLHs preferred RDV-free rice plants over RDV-infected rice plants. In odor selection preference bioassay using a four-field olfactometer, non-viruliferous GRLHs preferred odors of RDV-infected rice plants over healthy rice and viruliferous GRLHs preferred odors of RDV-free rice plants over RDV-infected ones. In 6 h plant penetration behavior bioassay using electrical penetration graphs, non-viruliferous GRLHs spent shorter time in non-penetration and much longer time in xylem feeding on RDV-infected, compared to RDV-free rice plants. Viruliferous GRLHs exhibited more salivation and stylet movement on RDV-free rice plants than on RDV-infected rice plants. We infer from these findings that RDV influences these vector behaviors by altering host plant physiology to promote viral transmission.
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Project description:Transgenic rice producing insecticidal proteins from Bacillus thuringiensis (Bt) could help protect the plants from damage by lepidopteran pests. However, one concern is the potential of Bt rice to harm non-target natural enemies, which play a vital role in pest control. In the present study, the potential effects of Cry1C rice and Cry2A rice on different life-table parameters and population dynamics of Pseudogonatopus flavifemur, a parasitoid of rice planthoppers, were evaluated under laboratory and field condition. The exposure of P. flavifemur to plant-produced Bt proteins was also analyzed. Results indicated that direct feeding on rice plants was the main exposure pathway of P. flavifemur to the Cry1C and Cry2A proteins. No significant difference on the development, survival, longevity, fecundity, and prey consumption of P. flavifemur was detected over two generations between the Bt and non-Bt rice treatments. Furthermore, the population dynamics of P. flavifemur were not affected by Cry1C rice and Cry2A rice. In conclusion, the tested Cry1C rice and Cry2A rice do not appear to harm the parasitoid P. flavifemur.
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Project description:Bt proteins are the most widely used insecticidal proteins in transgenic crops for improving insect resistance. We previously observed longer nymphal developmental duration and lower fecundity in brown planthopper (BPH) fed on Bt rice line KMD2, although Bt insecticidal protein Cry1Ab could rarely concentrate in this non-target rice pest. In the present study, we performed microarray analysis in an effort to detect Bt-independent variation, which might render Bt rice more defensive and/or less nutritious to BPH. We detected 3834 and 3273 differentially expressed probe-sets in response to BPH infestation in non-Bt parent Xiushui 11 and Bt rice KMD2, respectively, only 439 of which showed significant differences in expression between rice lines. Our analysis revealed a shift from growth to defense responses in response to BPH infestation, which was also detected in many other studies of plants suffering biotic and abiotic stresses. Chlorophyll biosynthesis and basic metabolism pathways were inhibited in response to infestation. IAA and GA levels decreased as a result of the repression of biosynthesis-related genes or the induction of inactivation-related genes. In accordance with these observations, a number of IAA-, GA-, BR-signaling genes were downregulated in response to BPH. Thus, the growth of rice plants under BPH attack was reduced and defense related hormone signaling like JA, SA and ET were activated. In addition, growth-related hormone signaling pathways, such as GA, BR, and auxin signaling pathways, as well as ABA, were also found to be involved in BPH-induced defense. On the other side, 51 probe-sets (represented 50 genes) that most likely contribute to the impact of Bt rice on BPH were identified, including three early nodulin genes, four lipid metabolic genes, 14 stress response genes, three TF genes and genes with other functions. Two transcription factor genes, bHLH and MYB, together with lipid transfer protein genes LTPL65 and early nodulin gene ENOD93, are the most likely candidates for improving herbivore resistance in plants.
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Project description:The parasitoid wasp Ampulex compressa hunts down its host, the American cockroach (Periplaneta americana), and envenomates its brain to make it a behaviorally compliant food supply for its offspring. The primary target of the wasp sting is a locomotory command center called the central complex (CX). In the present study, we employ, for the first time, chronic recordings of patterned cockroach CX activity in real time as the brain is infused with wasp venom. CX envenomation is followed by sequential changes in the pattern of neuronal firing that can be divided into three distinct temporal phases during the 2 h interval after venom injection: (1) reduction in neuronal activity for roughly 10 min immediately after venom injection; (2) rebound of activity lasting up to 25 min; (3) reduction of ongoing activity for up to 2 h. Long-term reduction of CX activity after venom injection is accompanied by decreased activity of both descending interneurons projecting to thoracic locomotory circuitry (DINs) and motor output. Thus, in this study, we provide a plausible chain of events starting in the CX that leads to decreased host locomotion following brain envenomation. We propose that these events account for the onset and maintenance of the prolonged hypokinetic state observed in stung cockroaches.
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