Population development of the cotton aphid, Aphis gossypii Glover, was studied in dryland cotton planted in late April, late May, and late June for seven consecutive years, 1988-1994. 'Paymaster 145' cotton was grown each year at the Texas Agricultural Experiment Station at Chillicothe. Abiotic factors that were monitored included maximum daily temperature, solar radiation, and day length. Biotic factors included percentage leaf moisture and nitrogen, predator abundance, and the square/boll ratio. Multiple regression and correlation analyses were used to determine the most influential variables affecting population development. The timing of peak population densities and peak densities of aphids were governed primarily by abiotic factors. Average aphid densities were regulated by an interaction of abiotic and biotic factors, but rate of aphid population decline was regulated by biotic factors.