A two year study monitoring fecundity and population density of cotton aphids, Aphis gossypii (Glover), was undertaken to determine if insecticides were stimulating aphid reproduction. In 1990, at the Plant Science Research Farm, Starkville, MS., aphid population density in Guthion 2L treated plots was significantly higher (ca. 36%) than in untreated plots. The highest population density was recorded at the middle canopy sampling level. Fecundity of aphids on Guthion 2L treated cotton was higher than that of the untreated check each week, but only significantly higher during week 5 (08/24-08/27). The average number of offspring produced per female per day was 1.90 and 1.25 in Guthion 2L treated plots and untreated check plots, respectively.

The 1991 study at the Black Belt Research Farm, Brooksville, MS., included 5 insecticides representing 4 classes. Aphid numbers in plots treated with Guthion 2L as well as plots treated with Ammo 2.5EC were significantly higher than untreated check plots on 22 August. On 29 August, aphid counts in Ammo 2.5EC, Guthion 2L and Thiodan 3.0EC treated plots were significantly higher than counts in check plots. The highest aphid population density was recorded for the lower canopy sampling level for the 1991 study. Significant differences in mean numbers of offspring/aphid/day were observed between some treatments each week except during week 4. Fecundity in Guthion 2L treated plots was statistically equal to or greater than all other treatments during the last 5 weeks, and was significantly different from the untreated check during the last 3 weeks. Aphids in most treated plots produced numerically more offspring day than those of check plots.