Some agronomic and environmental factors were studied under field conditions to determine their effect on the insecticide susceptibility of the cotton aphid, Aphis gossypii Glover. In all experiments, a rapid petri-dish bioassay technique was used to characterize the aphid response to Capture 2E (bifenthrin), Lorsban 4E (chlorpyrifos), Phaser 50W (endosulfan), Furadan 4F (carbofuran), and Provado 1.6F (imidacloprid). Dark aphids were less susceptible to most insecticides (Capture, Lorsban, Furadan, and Provado) than the light morphs. Aphids from late-planted cotton were less susceptible to all five insecticides than the aphids from the early planting, however, the difference in their response to Capture was not statistically significant. Nitrogen levels significantly affect the insecticide response for cotton aphids. Aphids from high nitrogen plots were less susceptible to Capture and Provado but more susceptible to endosulfan than the aphids from low nitrogen plots. Nitrogen also affected the population dynamics of naturally occurring aphids with higher densities in plots with higher levels of nitrogen. These changes in susceptibility may explain in part the erratic control with insecticides observed in the field.