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Host Discrimination Mechanism Of Microplitis Pallidipes To Distinguish Between Nucleopolyhedrovirus (NPV)-infected And Noninfected Larvae Of Spodoptera Exigua

Posted on:2017-05-17Degree:MasterType:Thesis
Country:ChinaCandidate:J H YangFull Text:PDF
GTID:2283330509456175Subject:Biology
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Parasitoids and insect viruses are important biocontrol agents of lepidopteran pests, and the combined controlling effects of the two biocontrol agents have been widely reported. So far, behavior responses of parasitoids to viru- infected insects have been much documented, but how parasitoids change their behavior responses had no cases confirmed under the background of global warming and even the mechanism of parasitoids responding to these changes has rarely been explored. In case of this point, the paper took Spodoptera exigua, Microplitis pallidipes and nucleopolyhedrovirus(NPV) as study system, observed parasitoids’ behavior to discriminate S. exigua, analyzed the effects of parasitoids’ learning experiences on its discrimination behavior, confirmed the selection behavior of parasitoids to both S. exigua and the plants damaged by S. exigua, and revealed the olfactory mechanism of S. exigua; its purpose is to provide evidences for the combined controlling effects and the corresponding mechanism of parasitoids and insect virus. The main results are as follows:1. we observed the effects of parasitoids on the behavior of distinguishing healthy and NPV-infected S. exigua under five temperatures(19, 23, 27, 31 and 35 ℃), and the results indicated that when the dose of 5.33×107 OB·ml-1 was conducted, under the two lower temperatures, the discrimination behavior of parasitoids to S. exigua was significant differences in the 96 th hour after larvae fed with the Se NPV, while under the other three higher temperature s, this discrimination behavior appeared significant differences in the 84 th hour after larvae fed with the Se NPV; and the significance of difference in parasitoids’ discrimination behavior lagged behind as the increase of the virus concentrations. As the increase of temperatures, the search time and tentacles beat time of parasitoids identify host was shortened, the probing times and parasitism rate increased, the preferred attacking rate to healthy host enhanced; meanwhile, the significant differences in the time of parasitoids discriminating healthy and NPV- infected S. exigua was shortened as the increases of temperatures.2. The effects of M. pallidipes two learning experiences on the discrimination between healthy and NPV- infected Spodoptera exigua larvae were investigated. The results indicated that in the learning experience of the parasitoids whose breeding hosts were healthy larvae, there were differences in the searching time, beating time of antenna, probing times, preferred attacking rate and parasitism rate on 84 h after treatment when the parasitoids discriminated between healthy and NPV-infected larvae, and that there were differences in the five indices on 84 h, 72 h, 72 h, 72 h and 84 h after treatment for the discrimination of the parasitoids whose breeding hosts were NPV-infected larvae; as to the learning experience of adult parasitoids on healthy larvae, there were differences in the five indices on 48 h, 24 h, 24 h, 24 h and 72 h after treatment, while the learning experience of adult parasitoids on NPV-infected larvae led to the differences on 84 h, 84 h, 72 h, 84 h and 84 h after treatment.3. The chemotactic responses of parasitoids to S. exigua and its damaged plant were tested. The selection of parasitoids to healthy and NPV- infected S. exigua larvae did not appear significant differences within 24~84h after NPV treatment, but appeared significant differences in the 96 th hour after NPV treatment; parasitoids would be more likely to choose healthy S. exigua larvae. As to the frass of S. exigua larvae, parasitoids preferred to healthy S. exigua larvae in the 84 th hour after NPV treatment. Parasitoids can not distinguish between Ipomoea aquatica Forsk leaf damaged by healthy and NPV-infected S. exigua larvae. For the composites of S. exigua larvae + I. aquatica which were damaged by S. exigua larvae, parasitoids preferred to healthy S. exigua larvae + I. aquatica which were damaged by healthy S. exigua larvae in the 84 th hour after NPV treatment.4. We cloned parasitoids odorant binding protein gene Mp OBP8 and Mp OBP10 full- length c DNA, and the sequence analysis showed that, Mp OBP8 and Mp OBP10 and Microplitis mediator and Microplitis demolitor part OBP with high sequence identity, and other insect OBP with low sequence identity. Tissue expression analysis presented that parasitoids Mp OBP8 and Mp OBP10 mainly expressed in the antennae, while in other tissues not detected.In conclusion, parasitoids’ learning experiences affected its ability to discriminate the hosts, this result tell us that when we used parasitoids and insect viruses tn control pests in the field, parasitoids learning experiences should be appropriately adjusted, so as to increase the controlling effects of parasitoids and insect viruses. Meanwhile, the temperature is an important ecological factor; the ability of parasitoids’ discrimination was enhanced with the increase of temperatures. This might predicted that with global warming, the behavioral response of parasitoids to host might be changed, the joint controlling ability of parasitoids and insect viruses might be promoted, which might reduce the damaging risk of S. exigua populations. In addition, the study also showed that after spraying insect viruses in the field, chemical communication changed between parasitoids and moths, crops and moths, and that such changes might influence the model of crops damaged by moths.
Keywords/Search Tags:Microplitis pallidipes, Spodoptera exigua, Spodoptera Exigua Nuclear Polyhedrosis Virus(Se NPV), host recognition, learning experiences, plant volatiles, odorant binding protein
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