The cotton aphid, Aphis gossypii Glover, has developed into a key pest of cotton in California during the 1990's. Studies were conducted to examine specific aspects of cotton aphid biology and the effects of cultural control measures on populations with the goal of incorporating these tools into robust IPM programs. Previous laboratory and small plot field studies have shown that high levels of nitrogen can increase aphid populations, therefore the possibility of using this as a cultural control measure was examined. Aphid populations in 1999 were characterized by overall low to moderate levels which developed fairly late in the season at a time when the soil nitrogen bank had likely largely been depleted/altered. Aphid levels were monitored in seven large plot grower field studies with four differential nitrogen regimes (50 to 200 lbs./A nitrogen). Low aphid populations developed late-season (Aug. and Sept.) in five of the seven fields. There was consistently a trend for more aphids in the 200 lbs./A nitrogen treatment compared with the 50 lb./A treatment with a 3-4X range across the treatments. Aphid densities in all cases were well below treatment thresholds. Detailed studies on cotton aphid population dynamics showed that generation times of aphids, from a laboratory colony placed into field cages, ranged from 12.3 to 9.3 days and the number of offspring per adult averaged 1.7 and 5.3 under 20 and 250 lbs./A nitrogen regimes, respectively. A negative effect of potassium on aphid fitness was seen and warrants further research. Finally, naturally-occurring aphid populations were monitored in plots with 0 (=20 lbs./A residual in soil), 50, 100, 150, and 200 lbs./A nitrogen. At the onset of aphid build-up, application of either a pyrethroid insecticide (Capture®) or a chloronicotinyl insecticide (Provado®) or no insecticide was superimposed. At 3 weeks following the insecticide application, in the untreated plots, aphid numbers increased slightly across the increasing nitrogen levels (10.9 to 24.8 aphids per leaf from 20 to 200 lbs./A N). Provado controlled the infestation as expected based on its activity spectrum. At 0 to 100 lbs./A N, the aphid population was 50-75% higher in the Capture-treated plots compared with untreated. However, at 150 and 200 lbs. N/A, there were 3 and 4 times, respectively, more aphids in the Capture plots compared with the untreated.