Studies On The Molecular Mechanisms Of Target Site-Associated Insecticide Resistance In Dimondback Moth, Plutella Xylostella (L.)

Plutelia xylosteila (L.) (Lepidoptera: Yponomeutidae), a major cosmopolitan pest of brassicas, represents one of the extreme cases of insecticide resistance in arthropods, and has received much attention in the past decade in toxicological studies. However, up to now, little is known about the molecular mechanism of insecticide resistance in this insect, which retards the resistance management and effective control. In this study, resistance survey, special synergist tests and enzyme analysis have been conducted on one susceptible strain and another resistant field swain of the dimondback moth, with the result indicating that target insensitivity might be the principal resistance mechanism of diamondback moth to pyrethroid and organophosphorus insecticides. On the base of this information, the sodium channel and acetylcholinesterase gene, which are the targets of these two insecticides, respectively, have been cloned and analyzed. Though the development of resistance to the major classes of insecticides in diamondback moth were studied and discussed by researchers from many countries, the insecticide application patterns tend to vary among populations, and the resistance status of the diamondback moth changes over different regions and populations, so the resistance levels of the dimondback moth from Nanjing to 135 deltamethrin . cypermethrin ~ dichlorvos and Chlorpyrifos-methyl, were investigated. The results tested by topical applications showed that the Nanjing strain has developed high resistance to deltamethrin (>176. 64-fold) and cypermethrin (112.04-fold), and moderate resistance to chlorpyrifos-methyl (22.59-fold). To understand the mechanism for the high-level pyrethroid resistance in diamondback moth, synergist tests were done, and it was founded that both TPP, an inhibitor of esterases, and PB, a MFO inhibitor, exhibited little or small synergism to deltaniethrin and cypermethrin, so nerve insensitivity might be the principal mechanism of pyrethroid resistance in P. xylostella. To find substitute insecticides providing good control of resistant diamondback moth, five insecticides newly introduced were used to test their contact toxicity with topical application method. Among the insecticides tested, two insecticides, abamectic and fipronil, were highly insecticidal to pyrethroid-resistant diamondback moth, with their LD50 values being 0.003 and 0.0052 j.tg/larva, respectively. Two insecticides, cartap and monosultap, were moderately insecticidal to resistant diamondback moth, with their LD50 values being 0.122 and 0.19 ~g /larva. The other insecticide, acetamiprid, was only slightly insecticidal, with its LD50 values being 1.979 p.g /larva. Past experience in diamondback moth resistance management had reinforced the belief that single-component strategies will fail. So, resistance management usually includes a number of tactics, such as alternation of insecticides, and use of mixtures. In the point of view resistance management, mixtures should be theoretically extremely effective in preventing development of resistance. But up to now, most mixtures were developed to control cotton pests in China, and few studies have been designed to answer questions regarding the best mixtures for controlling resistant diamondback moth. In this paper, the joint actions of four insecticides had been researched. The study suggested that six insecticide mixtures with ingredient ratios bas...