Abstract: The resistance level of cotton aphid Aphis gossypii to fenvalerate, omethoate and monocrotophos in Henan cotton growing areas was investigated during 1988 to 1990 and the result showed that there was a rapid increase of resistance to these three pesticides, especially to fenvalerate. A susceptible strain of the aphid wastreated for eight times with fenvalerate in the laboratory, the selection resuked in the increase of resistance level to 1393 fold and there was cross resistance of 2 to 4 fold to monocrotophos and omethoate. The life tables of experimental populations of four strains of different resistance levels were analyzed and the result indicated that there was no disadvantageous influence for resistance level of fenvalerate to the fitness of cotton aphids. Bioassays were carried out on the aphids resistant to fenvalerate with pyrethroids, organophosphates and amidines. The result showed that DDVP had a high toxicity, the mixtures of amidines and pyrethroids could have sig.Nificant synergism, but antogonism was found with the mixture containing DDVP.

Key words: Aphis gossypii——fenvalerate——intrinsic rate of natural increase ——insecticide resistance——synergism