Scanning Electron Microscopy Of Antennal And Behavioral Responses Of Megalurothrips Usitatus(bagnall) To Host Volatile Compounds

The bean flower thrips, Megalurothrips usitatus(Bagnall) is considered as one of the main pests distributed throughout South China regions. Losses caused by thrips feeding and oviposition can significantly reduce the market value and hinder the development of agricultural economy. M. usitatus poses an economic threat to a wide range of leguminous plants such as snap, cowpea, adzuki bean, and soybean. The number of thrips is becoming very high in short time due to short lifecycle and high reproduction rate. In recent years, chemical stategy is a very important control for M. usitatus. In order to reduce the use of chemical insecticides, we have to research for alternative stategies based on the chemical ecology management. Therefore, we carried out the research from insects and plants aspects. The main results of the study were as follow:Nine types of sensilla were discovered on the antennae of M. usitatus by using scanning electron microscopy, including B?hm bristles, Sensilla placodea, Sensilla trichoid, Sensilla chaetica, Sensilla basiconic, Sensilla styloconica, Sensilla cavity, Sensilla spore, Microtrichia. The morphology, distribution and number of sensilla on antennae of both sexes in thrips were measured and compared. These sensilla were discovered on antennae of male M. usitatus, while Sensilla cavity and Sensilla spore were not present in female. Antennae sensilla were mainly distributed on the flagellum, but there were rare on the scape and pedicel. There were significantly different on morphology, number, and distribution on different antennae segements.The olfactory behavioral response of M. usitatus for host plants by “Y”-type olfactometer, the results of study revealed that cowpea was more attractive to thrips than snap. The further study olfactory behavioral response for different development stage of the cowpea flower, the study showed that cowpea flowers have positive trend, while flower IV bud and flower bud with pest feeding have negative trend to this thrips.We collected host volatiles from flowers using a dynamic headspace collection method followed by Tenax-TA sorben extraction and aqueous methnol, n-hexane immersion extraction in study. Volatiles were analyed by gas chromatography–mass spectrometry(GC-MS) to determine their emission through two methods. One hundred and senventy two compounds were identified in the volatiles, including alcohol, aldehyde, acid, esters, aromatic, alkene, and ketone. There was a quantitative difference between the two collection methods. There were 68 and 104 kinds of compound were identified using a dynamic headspace collection and immersion extraction, respectively. There were the same kinds of compounds of host volatile in n-hexane and aqueous methnol extraction, such as o-Xylene, Palmitic acid, Docosyl acetate and Methyl palmitate, Methyl linoleate, Methyl stearate, respectively. Linalol and Docosyl acetate were identified in host volatile by dynamic headspace collection method, while Methyl palmitate, Hexadecanoic acid, Methyl linoleate, Phytol, and Linoleic acid through immersion extraction. The species of compounds were identified more in n-hexane extraction than in aqueous methnol.The olfactory behavioral responses of M. usitatus for compounds of host volatiles and others were studied by “Y”-type olfactometer. The main results found that thrips female adults have different responses for different volatiles extraction methods. The crude extract of n-hexane extraction have negative trend, whereas aqueous methnol have positive response. The study also revealed that Linalool, Beta-caryophyllene, Phytol and o-Xylenewere attractive to females M. usitatus. Ocimene, Methyl linoleate, Methyl palmitate, and 3-Hydroxy-2-Methyl-4-Pyrone were repellent to thrips. Different concentrations of the compound were revealed different effects on thrips. High concentrations of Ethyl palmitate were negative trend to M. usitatu, while low concentrations were attractive trend.The attractive of individually combine attractive and repellent compounds were carried out. In this study, we found that the combination of attractant o-Xylene and Beta-caryophyllene have significant repellent. Besides, o-Xylene and Ethyl palmitate combined with each other have negative trend. The combination of repellent compounds were no significantly attractive or repellent to M. usitatus.