Longest insect dormancy: Yucca moth larvae (Lepidoptera : Prodoxidae) metamorphose after 20, 25, and 30 years in diapause

Fully grown larvae of Prodoxus y-inversus (Riley) undergo diapause in harde ned cysts in the sterile tissue of Yucca baccata Torrey fruits. Dormancy no rmally lasts from early summer until the following May, but when optimal cl imatic ones, particularly winter chilling, are Dot received, the diapause i s maintained. Larvae of the 1969 generation were collected in April 1970 in southern Nevada and held in winter conditions that varied but were warmer than those to which the population wits adapted in Nevada. More than 180 in dividuals emerged synchronously following the 16th and 17th winters. Temper ature data suggested that the intensity of winter chilling is the primary f actor initiating diapause development and that after many years in diapause larvae are conditioned to respond to temperature regimes that A ere not ac ceptable for development in the early years of diapause. To test these hypo theses, larvae were held in constant warm temperatures for 4-5 yr, then exp osed to it variety of winter conditions. Additional large groups eclosed fo llowing their 20th (151 adults) and 25th (125 adults) winters. X-rays befor e the 30th winter indicated that few larvae remained, and 14 moths emerged following 30 yr in diapause.