Induction of Diapause in Field Populations of the Pink Bollworm 1 in the Western United States 23

The pink bollworm, Pectinophora gossypiella (Saunders) overwinters as a diapausing larva in a hibernaculum in cotton seeds, bolls, ground trash, or in the soil. In tests conducted in Arizona and southern California during 1973–78, the 1st diapause larvae was found as early as Aug. 23, and as late as Sept. 10. When diapause larvae were found in late Aug. the incidence of diapause remained low (<15%)until mid-Sept; after mid-Sept, the incidence of diapause rose rapidly to 50% or more by Oct. 1 and to 80% or more by mid-Oct. When temperatures averaged 29°C (85°F) or less during early Sept., the incidence of diapause began earlier than when the temperatures were higher. However, if average temperatures remained > 29°C during mid to late Sept., the incidence of diapause was low and increased when temperatures decreased and photoperiod shortened. Early irrigation termination, chemical termination treatments and varieties did not significantly affect the initiation-or the incidence of diapause.