RELATIONSHIP BETWEEN SUSCEPTIBILITY TO INSECTICIDES AND FECUNDITY ACROSS POPULATIONS OF COTTON APHID (HOMOPTERA, APHIDIDAE)

We measured the relationship between susceptibility to 4 insecticides and fecundity across 15 populations of cotton aphid, Aphis gossypii Cl over, from Hawaii. Multiple regression showed that the relationship be tween the logarithm of LC(50) and mean daily progeny production in the absence of insecticide exposure was negative for esfenvalerate (a pyr ethroid), positive for methomyl (a carbamate), and not significant for endosulfan (an organochlorine) or oxydemeton-methyl (an organophospha te). The association between methomyl susceptibility and fecundity was not evident in a simple regression analysis, which suggests that majo r fitness costs of resistance to one insecticide can obscure relations hips between fitness and resistance to other insecticides.