ABSTRACT.The larviposition of adult apterousMyzus persicaepreviously entrained to LD 18:6 showed a marked rhythm both under LD 12:12 (on plants reared in LD 18:6) and under LL (on plants reared in LL). No rhythm was detectable in larviposition by adults reared in LL. Larviposition peaked towards the end of the photophase in LD 12:12. Fresh‐weight gain also showed a circadian rhythm with the greatest weight increases during the photophase. Re‐entrainment from LD 12:12 to DL 12:12 was not complete after 10 days. It is concluded that the changes in the light cycle did not affect the aphids through the pl