Resistance Biochemical Mechanisms And Relative Fitness Of The Peach-Potato Aphid, Myzus Persicae (Homoptera: Aphididae) To Imidacloprid

The peach-potato aphid; Myzus persicae (Sulzer), is a cosmopolitan polyphagous species and an important pest of many crops. In addition, the species is a major vector of many economic plant viruses. For example, the tobacco populations of Myzus persicae are considered as the most important pest of tobacco in Yunnan Province, China, causing direct as well as indirect damage to the plants by transmitting important non-persistent viruses. The development of imidacloprid has provided growers with a new tool for managing some of the world's most destructive crop pests, primarily those of the order Hemiptera (aphids, whiteflies, and planthoppers) and Coleoptera (beetles). But, several insect pests have evolved the resistance to imidacloprid now in greenhouse and in field. In this paper, imidacloprid-resistant strain of the peach-potato aphid, Myzus persicae was selected under laboratory conditions, cross-resistance, biochemical mechanisms and relative fitness of resistance to imidacloprid in Myzus persicae were studied.The susceptiable strain of Myzus persicae, was selected with imidacloprid to determine if resistance would develop when maintained under continuous selection pressure by leaf-dip bioassay in a greenhouse. The imidacloprid-resistant strain with resistance ratio at 16.26-fold was developed after 18 gengrations selection. The cross-resistances of the imidacloprid-resistant strains to nine insecticides commonly used in the tobacco field were also measured. It appeared to have positive cross-resistance to pyrethroids including lambda-cyhalothrin and deltamethrin; It also had cross-resistance to organophosphates such as omethoate, phoxim, methamidophos and the mixture of imidacloprid and beta-cypermethrin. However, it had no cross-resistance to carbamate (methomyl), organochlorine (endosulfan) and the mixture of abamectin and phoxim.Biochemical mechanisms in Myzus persicae resistant to imidacloprid were investigated. Activities of resistance-related enzymes and their frequency distributions, the kinetic parameters, Vmax and Km of some enzymes were compared among different selection generations and susceptiable strain. A highermetabolic rate of imidaclopnd in the imidaclopnd-resistant strains can be expected by the fact that activities of glutathione S-transferase, carboxylesterase and acetylcholinesterase in resistant strains were significantly higher than these in the susceptible one. The activities enhancement of glutathione S-transferase would be the main metabolic mechanism in the resistance of Myzus persicae to imidaclopnd and the activities enhancement of carboxylesterase and acetylcholinesterase were relational to the resistance. There were also some changes in the quality of carboxylesterase in resistance strains. But we didn't find susceptibility decrease of acetylcholinesterase in resistant strains. Piperonyl butoxide (PBO) had a little synergism to imidaloprid in any of the strains. Considering there was no significant difference between the activities of mixed-function oxidase in the imidacloprid-resistant strain and susceptible strain. We presumed that the changes of mixed-function oxidase activity were not the mechanism in the resistance of Myzus persicae to imidaclopnd.The effects of resistance on the fitness of Myzus persicae were evaluated in terms of developmental and reproductive characteristics by constructing and comparing the life tables of imidacloprid-resistant and susceptible strain. The results revealed that the imidacloprid-resistant strain had no developmental disadvantages but obvious reproductive disadvantages compared to susceptible strain. The mean length generation time and life-span of adult apterae of the imidacloprid-resistant strain were 8.41 d and 20.57 d, and those of susceptible strain were 8.22 d and 21.75 d, respectively, but there were no significant difference. The mean progeny in entire generation and in every single day during fecundity stage of the imidacloprid-resistant strain were 67.67 aphid per apterae, 4.20 aphid per apterae per day, and those of susceptible stra...