The toxicities of two commonly used soil insecticides, fonofos and phorate, were compared among one larval population of the corn wireworm, Melanotus communis (Gyllenhal), from sugarcane fields and three populations from potato fields in southern Florida. Fonofos toxicity did not differ among most populations; however, phorate toxicity did. Phorate was consistently less toxic to one population from potato fields. The toxicities of these two compounds to the population from sugarcane fields did not differ from those from potato fields, despite differences in insecticide pressure between the two crops.