| The swarming locusts represent a group of prominent worldwide agriculture pests. Due to the extended high temperature, long-lasting drought and the consequent alternations in locust breeding environment the destructive outbreaks of locust had been increasing in China since 1990s, especially in the north, which seriously threaten the agriculture production. So far the chemical controls are still the major measures taken in locust abatement programs in China. In spite of the effectiveness and convenience, the frequent use of insecticides both in quantity and variety has caused a series of problems like locust resistance development, increased control difficulty and rising cost. Recently, the Chinese plant protection agencies reported the growing hardships in controlling some field populations of oriental migratory locust with organophosphate (OP) compounds.Up to now there are more than 600 arthropod species with documented resistance to one or more insecticides and/or acaricides since resistance phenomenon was first described in San Jose scale to lime-sulfur in Washington in 1908. Enhanced metabolic detoxification and reduced sensitivity of insecticide target-sites are the two major mechanisms in resistance development, involving three primary metabolic enzymes of esterases, glutathione S-transferases and cytochrome P450 polysubstrate monooxygenases. Resistance would be developed when the activities of any of these three enzymes are increased. The three insecticide target-sites are acetylcholinesterase (AChE) for organophosphate and carbamate insecticides, voltage-gated sodium channels: knockdown resistance (kdr or kdr-type) for DDT & pyrethroids and y-aminobutyric acid (GABA) receptors for cyclodienes. The resistance mechanisms have been particularly studied in fruit fly, housefly, cotton bollworm, diamond back moth and mosquitoes, which have rendered abundant references for the research in this field.This dissertation studied biochemical characters of enzymes associated to OP resistance in field populations of Locusta migratoria manilensis (Meyen) from Huanghua-Hebei, Pingshan-Hebei, Beidagang-Tianjin and Wudi-Shandong, where the insecticide selection pressures are considered different. Huanghua-Hebei, Beidagang-Tinjin and Wudi-Shandong are close to Bohai Bay, classified in sea-coast locust area with the similar ecological characteristics. Pingshan-Hebei, on the other hand is at the verge of Gangnan reservoir, classified in river-flood area. The two areas are important in locust control in China because of the frequent massive outbreaks of Locusta migratoria manilensis (Meyen). The selection pressure of OP was found higher in Huanghua-Hebei and Beidagang-Tianjin than in Pingshan-Hebei and Wudi-Shandong. LD50 values for malathion of Huanghua-Hebei and Beidagang-Tianjin are higher than those of Pingshan-Hebei and Wudi-Shandong. LD50 values for malathion of Beidagang-Tianjin, Huanghua-Hebei andPingshan-Hebei were each 1.96-, 1.8- and 1.02-fold higher than that of Wudi-Shandong.General esterases of oriental migratory locust collected from the four locations were compared. General esterases were most concentrated in the thorax and abdomen, which showed 46.1% and 36.1% of total esterase activity in females, and 42.7 and 36.0% in males, when using -NA as substrate. Kinetic studies demonstrated that general esterases in four oriental migratory locust populations hydrolyze -NA, -NB, P-NA and p-NA as substrate. Among the four substrates, -NA seemed to be the most favorable substrate for general esterases of the locust. In contrast, p-NA is not a preferred substrate for these esterases, with the lowest Vmax and the highest Km in both Huanghua-Hebei and Pingshan-Hebei populations. Inhibition studies of the esterases using four inhibitors (i. e., paraoxon, malaoxon, eserine, and carbaryl) indicated that most of general esterases in the four populations were B-type. Moreover, significant difference in general esterases activities was observed among four populations. Wudi-Shandong population...
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