ENVIRONMENTAL-REGULATION AND GEOGRAPHICAL ADAPTATION OF DIAPAUSE IN COTESIA-PLUTELLAE (HYMENOPTERA, BRACONIDAE), A PARASITOID OF THE DIAMONDBACK MOTH LARVAE

Photoperiodic response in two different geographic populations of Cote sia plutellae (Hymenoptera: Braconidae) was investigated. Short photop eriods induced prepupal diapause in the Kuroishi population but did no t produce any developmental arrest in the Kobe population. The differe nce in the photoperiodic response in these populations reflects life-c ycle adaptations to local environmental conditions. In the Kuroishi st rain the critical daylength fell between 12.5 h and 13 h hours of ligh t per day, Under 11L-13D conditions, high temperatures tended to decre ase the occurrence of the diapause: as the temperature increased from 17-degrees-C to 20-degrees-C the diapause incidence diminished, ceasin g altogether at 25-degrees-C. Parasite larvae of second and third inst ar stages were sensitive to diapause-inducing stimuli, whereas egg and first instar larval stages were not. The diapause termination depende d not on the photoperiod but on the temperature: high temperature hast ened termination of the diapause.