ABSTRACT

The study was conducted at the Texas Agricultural Experiment Station, Chillicothe, in the northern Texas Rolling Plains for four years from 1997 to 2000. The objective was to determine the relationship between nonstructural carbohydrates (glucose, fructose, sucrose) in cotton leaves and change in cotton aphid, Aphis gossypii Glover, numbers during late summer. The two whole plot treatments were cotton grown without irrigation (dryland) and irrigated cotton with last irrigation in late August. The two subplot treatments within each whole plot were an untreated check and a plot treated twice during the growing season with lambda-cyhalothrin to stimulate aphid population increase. The sugar ratio (glucose + fructose/sucrose concentrations) was higher in irrigated plots compared with levels in dryland plots. Regression analysis indicated that change in aphid numbers was influenced by numbers of aphids per leaf, temperature, leaf moisture, and sugar ratio. A negative linear relationship was observed between change in aphid numbers and sugar ratio; population growth was limited by high levels of glucose and fructose in cotton leaves, especially when temperatures were high and leaf moisture low.