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 Cotesia plutellae (Hymenoptera: Braconidae) was investigated. Short photoperiods induced prepupal diapause in the Kuroishi population but did not produce any developmental arrest in the Kobe population. The difference in the photoperiodic response in these populations reflects life-cycle adaptations to local environmental conditions. In the Kuroishi strain the critical daylength fell between 12.5 h and 13 h hours of light per day, Under 11L-13D conditions, high temperatures tended to decrease the occurrence of the diapause: as the temperature increased from 17-degrees-C to 20-degrees-C the diapause incidence diminished, ceasing altogether at 25-degrees-C. Parasite larvae of second and third instar stages were sensitive to diapause-inducing stimuli, whereas egg and first instar larval stages were not. The diapause termination depended not on the photoperiod but on the temperature: high temperature hastened termination of the diapause.