| The oriental migratory locust, Locusia migratoria manifensis, is a major insect pest in China, which seriously threatens the agriculture production. In the south of Shanxi province, the locust occurred two generations every year, which was eruptive locust disaster.Till now, the chemical controls are the major measures taken in locust managements. The vast use of insecticides has caused a series of problems like the development of the locust resistance to organophosphate compounds, which has been focused on by the local plant protection agencies.Enhanced metabolic detoxification and reduced sensitivity of insecticide target-sites are the two major mechanisms in resistance development. The former included metabolic enzymes of esterases and glutathione-S-transferases (GSTs). The latter contained acetylcholinesterase (AChE) which is the target-site of organophosphate insecticides. The resistance mechanisms have been widely studied in fruit fly and mosquitoes.This dissertation studied biochemical characters of enzymes associated with organophosphate compounds resistance in field populations of Locusta migratoria manilensis (Meyen) from Yongji and Linyi both in Shanxi Province, where the insecticide selection pressures are significantly different. The habitat of the Yongji population belongs to an inland plain flood locust area, and insecticides are often used in locust control, whereas that of Linyi population belongs to a flood river locust area and insecticides are seldom used for locust control. The selection pressure of organophosphate insecticiedes was higher in Yongji than in Linyi.Significant difference in general esterases activities was observed between the two populations. In the whole, Yongji population showed the higher general esterase activities than Linyi population. The esterases activities of the females were 2.30-, 2.09-, and 0.66- fold higher in Yongji population than in Linyi population using a-NA, a-NB, and B-NA as substrates; and the esterases activities of the males were 3.24-, 2.56-, and 1.56-fold higher in Yongji population than in Linyi population by using the same substrates: a-NA, a-NB, and B-NA. The distributing spectrum of general esterases activities showed significant difference among two populations. Yongji population had more individuals with high esterase activities than Linyi population. Kinetic studies demonstrated that general esterases in two populations all could hydrolyze a-NA, a-NB, and B-NA as substrate. Among the three substrates, a-NB seemed to be the most favorable substrate for Yongji population; and a-NA is a preferred substrate for Linyi population. The Kmax values were higher in Yongji population than in Linyi population, using a-NA, -NB, and -NA as substrates. Inhibition studies of the esterases using four inhibitors (i. E., paraoxon, malaoxon, eserine, and carbaryl) indicated that most of general esterases in the two populations were B-type. Non-denaturing PAGE analyses of general esterases from Yongji and Linyi samples showed similar band patterns. Increased esterase activity in Yongji population appeared to be due to some additional esterases as shown on the nondenaturing PAGE of the esterases in individual locusts.Between the two populations, there was no significant difference in ghitathione-S-ttansfetase activities. The activities of glutathione-S-transferase in Yongji population were 1.03-fold higherfor females; and 0.86-fold higher for males than those in Linyi population. In the spectrum of glutathione-S-transferase activities, there was also no significant difference. It indicated that the glutathione-S-transferase seemed not to be associated with organophosphate compounds sensitivity.Acetylcholinesterase (AChE) was compared. The Km value was higher in Yongji population than in Linyi population, but the K,nax value was lower in Yongji population than in Linyi population, using ATC as substrate. The inhibition of AChE activity by selected substrate at high concentration was found both in Yongji and Linyi populations. The sensitivity...
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