JUVENILE HORMONE CHANGESASSOCIATED WITH DIAPAUSEINDUCTION, MAINTENANCE,AND TERMINATION IN THE BEETWEBWORM, Loxostege sticticalis(LEPIDOPTERA: PYRALIDAE)

摘要

At 22 deg C and under a long-day photoperiod of L:D 16:8, all the last fifthinstar Loxostege sticticalis larvae undergo prepupal stage and pupatewithout diapause. Under a short-day photoperiod of L:D 12:12, incontrast, they all enter diapause with approximately 36 days diapausemaintenance and then terminate diapause spontaneously, although only44% of the larvae terminated diapause successfully. Changes inhemolymph juvenile hormone (JH I) titers of diapause-destined larvaeacross diapause induction, maintenance and termination were examinedusing HPLC, and were compared with those of non-diapause-destinedlarvae from the fifth instar through pupation. JH I titer of the earliestfifth instar diapause-destined larvae remained at a high level with a peakof 220.4 ng/ml, though it decreased continuously to a minimum of69.0 ng/ml on day 5 in the fifth instar when the larvae stopped feeding toenter diapause. During the diapause maintenance, JH I titer of themature larvae increased significantly and maintained a high level untilday 31 in prepupae. JH I titer declined and fluctuated at low level from5 days before pupation. In contrast, JH I titer of both the fifth instar non-diapause-destined larvae and prepupae remained and fluctuated at low level consistently, as well as decreased before pupation. These resultsindicate that diapause induction and maintenance in this species mightbe a consequence of high JH, whereas diapause termination can beattributed to low JH titer, which was in agreement with the hormonalregulation observed in many other larval-diapausing insects.