Seasonal dynamics of the cotton aphid, Aphis gossypii Glover, the entomopathogenic fungus Neozygites fresenii (Nowakowski) Batko, the parasite Lysiphlebus testaceipes (Cresson), and key environmental factors were investigated for two years in the Mississippi Delta. A. gossypii populations peaked in mid-July and in mid- to late-August in l991 and 1992. A. gossypii populations were concentrated in the lower plant canopy throughout the 1991 and 1992 growing season. Parasitism peaked only in mid-July, coinciding with the early season aphid population peak. Parasitism was at or near zero during the August peak aphid population period. N. fresenii peak prevalence in 1992 was approximately six times lower than in 1991, but coincided with peak aphid population density during both years. Leaf wetness was positively correlated with fungal prevalence. It appears that host density and leaf wetness may be two of the more important factors regulating N. fresenii prevalence in A. gossypii. Levels of parasitism and fungal infection in A. gossypii indicate that additional factors contribute to its population regulation. Two A. gossypii and N. fresenii seasonal dynamics scenarios are described for the Mississippi Delta. This information should serve in part as a basis for development of a predictive model that will aid cotton growers in pest management decisions regarding cotton aphid.