STUDY ON THE RESURGENCE CAUSED BY INSECTICIDES FOR COTTON APHID, APHIS GOSSYPII
杀虫剂诱使棉蚜再猖獗的研究

Fenvalerate, omethoate and monocrotophos are the major pesticides for the chemical control of cotton aphid in Henan province. The experiment of application of these pesticides was done in cotton field in 1990, the result showed that plots by a successive three time spray with fenvalerate and four sprays with omethoate would induce the aphid population outbreak. The contrary was obtained in plots treated successively with monocrotophos. After the fourth time of using pesticide, population densities in two treatments with fenvalerate were 9.05 and 7.22 fold respectively compared to the control plots. The detection of resistance for the aphid indicated that as the times of applying insecticide increased, the level of resistance rose quickly, after the fourth time, the LD50 was 9.39 times that of early season before chemical control. Laboratory study found that pesticides were remarkably high toxic to nutural enemy such as Coceinella septempunctata and Leis axy-ridis. The analysis of life tables for adult and nymph treated respectively by the three pesticides pointed out that the rm value and other population parameters were not obviously different with the aphid untreated, there was no stimulating increase to the aphid fecundity.According to the result of experiment above, it is suggested that fenvalerate is unsuitable to control cotton aphid, the main reasons for inducing resurgence are the killing of natural enemies, destroying of cotton ecosystem, and making fast increase of insect pest resistance to insecticides.