Studies On Molecular Mechanism Of Resistance To Avermectin In Plutella Xylostella

Plutella xylostella (Linnaeus) is one of the most important pests on cruciferous vegetables. And it also was one of the most serious emergence and development of drug-resistant pests. Avermectins is the key insecticide which has been widely used to control this pest, Plutella xylostella has a serious resistant to avermectins. In order to reveal the resistance mechanism of Plutella xylostella to avermectins, In this article we use laboratory selection and studied the cross-resistance of Pmtella xytartala to avermectins. We cloned the full-length GluClαgene from the resistant and susceptible strains of Plutella xylostella, and the sequences were aligned and analyzed. The mRNA levels of the GluClαgene from resistant and susceptible strains were compared through the real-time PCR technique. The results were as follows.(1) The development of resistance to avermectins (AVMs) in diamondback moth, Plutella xylostella (L.) was evaluated from log dosage-probit mortality curves constructed from the resp-onse of DBM larvae to AVMs treatment. The insects used for the study were taken from laboratory selected resistant and laboratory reared susceptible strains. The results showed that Diamondback moth resistance to avermectins, was after a slow start and fast. The sensitivities of AVMs re-sistant strains to 5 insecticides had been tested. The results showed that the resistant strain had vary degree crosses-resistance to spinosad, Proclaim R and indoxacarb, with a dimension of the salt in multiples of the highest cross-resistance, amounting to 8.85 times; and it was no crosses-resistance on the resistance strain to Chlorfenapyr and Fiprronil.(2) For the first time, using RT-PCR and RACE technique, glutamate-gated chloride channel receptor gene subunit from susceptive and resistant strain of P. xylostella was cloned and sequenced. This gene was of 2167bp with open reading frame 1344bp encoding 447 amino acid. It had the conserved amino acids and typical features shared by the GluClαfamily and alpha-subunit. And the homology to the GluClαsubunit gene of other insects was 70%-80%. Seven nucleotides were found to be different between the resistant and susceptible strains. Three of them lead to three amino acids mutated. The positions of replaced amino acids were 186 C replacement of Y, 336 P replacement of S and 388 R replacement of Q in resistant strains. The similarity of nucleotides and identity of amino acids of sequences were 99.48% and 99.33%.(3) The mRNA expression levels of GluClαgene were compared between the resistant and susceptible strain of P.xylostella using real-time fluoro-genetic quantitative PCR. The results showed that the mRNA expression of GluClαin resistant strain was 3.31-fold higher than the susceptible strain. The mRNA expression levels preliminarily suggested that the over-expression of GluClαwas probably associated with high resistance to thiamethoxam.