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 Glover, from Hawaii. Multiple regression showed that the relationship between the logarithm of LC₅₀ and mean daily progeny production in the absence of insecticide exposure was negative for esfenvalerate (a pyrethroid), positive for methomyl (a carbamate), and not significant for endosulfan (an organochlorine) or oxydemeton-methyl (an organophosphate). The association between methomyl susceptibility and fecundity was not evident in a simple regression analysis, which suggests that major fitness costs of resistance to one insecticide can obscure relationships between fitness and resistance to other insecticides.