Activity patterns of fifth-instar tobacco budworms,Heliothis virescens(F.), and cabbage loopers,Trichoplusia ni(Hübner), were determined in the laboratory with an ultrasonic actograph and in the field by visual observations of marked larvae. Field data correlated well with laboratory data and showed that larvae of both species were active predominantly during periods of illumination. Activity patterns of larvae and timing of pesticide treatments for increased efficacy are discussed