Patterns of Field Diapause in the Navel Orangeworm (Lepidoptera: Phycitidae) and Three Imported Parasites1

Variable percentages of field-collected larvae of the navel orangeworm, Amyelois transitella (Walker), and the parasites Pentalitomastix plethorica Caltagirone (Hymenoptera: Encyrtidae), Goniozus emigratus (Rohwer) (Hymenoptera: Bethylidae), and G. legneri Gordh (Hymenoptera: Bethylidae), required significantly longer developmental periods to the adult stage than those in laboratory control cultures. The difference indicates diapause in the host triggered by several seasonally varying factors, and a diapause in the parasites triggered by hormonal changes in the host. Possible latitudinal effects on diapause were observed. The ability of newly imported parasites to diapause with their host may enable their permanent establishment, and eventually the reduction of host population densities.