Both adult and third instar larval Heliothis virescens were examined for nerve insensitivity to cis-cypermethrin using a rapid and robust neurophysiological method. Two laboratory strains BRC susceptible and PEG resistant and a pyrethroid resistant field strain from Red River Louisiana were compared. Nerve insensitivity was present in a proportion of the individuals in both the PEG and Red River strain, at both life stages, and absent in the BRC strain. Frequencies of nerve sensitive and nerve insensitive individuals in each strain were not significantly different at the two life stages examined.