Hybrids were obtained by crossing males of the turnip moth Agrotis segetum, which has a period of arrested development in the larval stage, with females of the migrant and nondiapausing black cutworm, Agrotis ipsilon. No progeny were obtained by crossing females of A. segetum with males of A. ipsilon. Backcrosses were successful only by crossing hybrids with both sexes of A. ipsilon. No larval oligopause occurred when hybrid larvae were reared under conditions inducing arrest in A. segetum (12L:12D, 21°C). Wind tunnel tests showed interattractiveness of F1 hybrids with A. ipsilon but not with A. segetum. Single sensillum recordings of pheromone-sensitive hairs on the antennae of males of the parent species revealed differences in the distribution of sensilla. F1 and F2 hybrids exhibited the same receptor cell types and distribution as A. ipsilon. Gas chromatographic analysis of female pheromone gland extracts revealed that F1 hybrids were also very close to A. ipsilon.