Seasonal changes of methamidophos susceptibility in Plutella xylostella and its parasitoid Cotesia plutellae

摘要

Methamidophos resistance was monitored in field populations of Plutella xylostella and Cotesia plutellae collected on corresponding hosts from Fujian Province, China. Methamidophos resistance levels in two insect species were high during autumn and spring and low in summer. Resistance to methamidophos was 15. 3-and 12.6-fold higher in F0 parents of P. xylostella and C. plutellae than in their susceptible F,, progeny, respectively. The bimolecular rate constant (AJ values of acetylcholinesterase ( AChE) to methamidophos, dichlorvos, and carbofuran were 4. 6-, 6. 3-, and 7. 7-fold higher in F,, progeny of P. xylostella, and 3. 7-, 4.5-, and 3. 7-fold higher in Fn progeny of C. plutellae than those in their F0 parents, respectively. Compared with susceptible Fn progeny, the resistance ratios for methamidophos were 4. 2-29. 8 and 3. 8-13. 1 in 21 field populations of P. xylostella and C. plutellae, respectively. The molecular rate constant (A);) values of AChE to methamidohos, dichlorvos, and carbofuran were 2. 0-21. 6, 3. 6-9. 5-fold higher in F_n progeny of P. xylostella, and 1. 8-7. 6-, 1. 9-4. 6-, and 2. 2-7. 6-fold higher in F_n progeny of C. plutellae than those in 21 field populations, respectively. We found significant correlative variations of resistance as well as significant correlative variations of k_t values of AChE to organophosphorus insecticides between two species of insects in space and time. There were no obvious differences in K_m and V_(mm) of AChE between F_0 parents and F_1 progeny of P. xylostella and C. plutellae, respectively. But carboxylesterase activity was 1.6-fold higher in F_0 parents of C. plutellae than in F_n progeny, and glutathione S-transferase activity was 1.5-fold higher in F_0 parents of P. xylostella than in F_n progeny. From these results, insensitive AChE to methamidophos was thought to be the most important resistance mechanism in P. xylostella and C. plutellae.