Esterases present in the hemolymph of last instar Heliothis zea (Boddie) were separated by polyacrylamide gel electrophoresis. Four systems, all polymorphic, were observed. One system, Est-II, appeared especially suited for the study of some of the important population processes of this species; these include host–plant relations, migration, and the effects of environmental pressures such as pesticides on the species.
Est-II was classified as a carboxylesterase, being sensitive only to organophosphate inhibitors. Dichlorvos at 10−5M completely inhibited Est-II activity.
Populations collected from corn from Tifton, Ga., and in two locations in Illinois, at approximately the same time were very similar genetically when compared on the basis of Est-II allele frequencies. A population collected from leguminous hosts in Tifton, Ga., at the same time as the above three populations was different genetically.
Est-IIc, an allele normally rare or absent in the populations studied, was present at a high frequency in one Urbana population collection. Est-IIc may be useful in studying the long-range dispersal of H. zea.