Humidity-terminated diapause in the tropical braconid parasitoid Microplitis demolitor

1. Microplitis demolitor, a solitary braconid parasitoid of Helicoverpa arm igera and Helicoverpa punctigera, uses an increase in relative humidity to signal the end of diapause and the re-establishment of direct development. 2. Photoperiod and temperature changes appear not to have a direct influenc e on the duration or termination of diapause in this species. 3. Once diapause termination is signalled, the adult parasitoids emerge app roximately 38 days later. 4. The cue for diapause termination in M. demolitor is different from that used by its hosts and ensures that the parasitoid emerges to find a populat ion of nonmigrating hosts. 5. It appears that the cocoon surrounding the diapausing parasitoid plays a role in diapause termination; parasitoids emerge earlier from diapause if the cocoon is removed but the weight of the intact cocoon does not appear t o influence the length of time the parasitoid is in diapause.