Maternal photoperiod effect on and geographic variation of diapause incidence in Cotesia plutellae (Hymenoptera: Braconidae) from China

Effects of maternal photoperiod on the diapause trait of Cotesia plutellae in two populations, one from Hangzhou (30°14′ N), Zhejiang Province, and the other from Changchun (43°52′ N), Jilin Province, China, were examined in the laboratory by exposing the mother generation (G0) to 3 day-lengths (8L-16D, 12L-12D, and 16L-8D) at 25°C, and exposing their offspring (G1) to 2 day-lengths (8L-16D, 11L-13D) at 4 temperatures (13, 15, 17, 20°C). All three diapause-inducing factors had a significant influence on the incidence of diapause. Both populations could be induced to enter diapause under pertinent conditions. Long day length in G0 decreased the incidence of diapause and lowered the critical temperature for diapause-induction in G1. There were significant differences in the incidence of diapause between the two populations in almost all combinations. Compared to the southern Hangzhou population, the northern Changchun population produced a higher proportion of diapause individuals, and had higher critical temperatures for diapause-induction in all 6 photoperiod combinations used in G0 and G1 except for the one in which short day length (8L-16D) was used in both generations.