Insecticide Resistance of the Cotton Bollworm Larvae (Heliothis armigera)

Abstract

Toxicological testing of resistance to insecticides by cotton bollworm larvae was studied. Larvae were collected from cotton growing areas in provinces of Nakon Sawan, Lopburi, Loei, Sukhothai, Chantaburi and Chiang Mai. During the 1986 and 1987 growing seasons. The insecticides tested were fenvalerate, deltamethrin, cypermethrin, sulprofos, triazophos and endosulfan. Median-lethal-dose (LD₅₀) and resistance ratio were used to determine resistance levels and relative toxicity of the insecticides to the bollworm larvae from different cotton growing areas.
The LD50 of the insecticides on the bollworm larvae differed, reflecting differences in insecticide use in the different locations. The general level of resistance to pyrethroids was greater than for the other insecticides tested in the study.