Study On Ogranophosphorus Resistances Of Spodoptera Litura And Clone And Sequence Analysis Of Acetylcholinesterase Gene

Spodoptera litura is one of the most important pests of vegetables, plants and many crops. It abounds in the world recently and causes serious damages. Because of the large-scale adoption and irrational application of chemical pesticides, the level of drug resistance of Spodoptera litura increase obviously, which results in the difficulties of pest control. In order to understand the different resistance level of commonly used organophosphorus pesticides to the different regions of Spodoptera litura, the effect of three kinds of pesticides, such as Acephate, to the 3rd instar larvae of Suzhou's and other places' Spodoptera litura were determined by leaf - dipping method. The results showed that the order of toxicity from high to low was Lorsban, Phoxim, Acephate 24 hour later. We found that the LC50 of Acephate is generally high for the four regions of Spodoptera litura populations, and their resistance ratio to achieve 56.23-109.46 fold, so this pesticidesshouldbe useless in these area. The LC50 of Lorsban is 43.93-236.64 mg?L-1 and the resistance ratio is 1.03-5.57 fold, and the LC50 and the resistance ratio of Phoxim is 131.71-880.75 mg?L-1 and 3.10-20.74 fold, both of which can be used continuously. In addition, the paper analyze the different causes of the resistance of different populations of Spodoptera litura, and relevant measures are put forward to improve efficiency and control the rising of the resistance.Insect acetylcholinesterase (AChE, EC3.1.1.7)is the target of Organophosphorus and Carbamate Insecticides. Using RT-PCR, the partial cDNA sequence of the acetylcholinesterase gene (GenBank accession number is FJ959384) in the Spodoptera litura was cloned by designing degenerate primer. After restricting enzyme digestion, sequencing and sequence analysis of results showed that AChE fragment is 1 191 bp in length with an open reading frame encoding a 397 amino acid protein which includes the characteristic regions of acetylcholinesterase. The alignment analysis showed high postional identities in several conserved regions. AChE is a useful model for studying the enzyme degrdation and a credible phylogenetic tree was constructed based on ME method in MEGA 4.The results provide an important theoretical reference for further study of AchE enzyme characteristics. The similarity of Spodoptera litura AchE nucleotide sequence and of amino acids was over 68% and 80% compared with Spodoptera exigua, Bombyx mori, Plutella xylostella, Helicoverpa assulta, Chilo suppressalis, Helicoverpa armigera and Blattella germanica AchE genes. The results provide an important theoretical reference for further study of acetylcholinesterase's structure and function and also provide basis for the further study of the molecular mechanism research on the insecticide resistance of AChE.