Submitted to: Entomology International Congress Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: March 1, 1999
Publication Date: N/A
A system of markers has been devised to track the development of 4th instar and pharate adult greenhouse (Trialeurodes vaporariorum) and silverleaf whiteflies (Bemisia argentifolii). Measurement of body length and depth as well as color of the developing adult eye were used to divide the instar into 9 stages. Maximum body thickness was attained in stage 5 whiteflies, and adult eye development commenced at stage six. The adult eye was fully developed by stage 8. An enzymeimmunoassay was used to measure ecdysteroid titers in whole body homogenates of greenhouse whiteflies. Titers ranged from 68 to 380 femtograms per whitefly. In the early part of the 4th instar, titers were relatively low. Titers increased as the body thickened, peaked at stage 5 and decreased during pharate adult development. Based on an external examination of developing 4th instars and the fluctuations in ecdysteroid titer, it appears that apolysis (the separation of the larval cuticle from the epidermis, i.e., the initiation of the molt to the pharate adult) probably occurs in stage-5 4th instars. Results from histological studies support this view. Stage-4 4th instars possessed eye and wing development characteristic of earlier, immature stages. By stage-5, adult eye and wing development had been initiated. In stage-6 4th instars, the wing buds were deeply folded, and by stage 7, spines were observed on the new cuticle, indicating that the adult cuticle was well-formed by this stage. Typically, in preparations of stage 6 or older 4th instars (actually pharate adults), the larval cuticle was either separated from the epidermis or had become detached during processing. Histological studies of B. argentifolii 4th instars/pharate adults yielded similar results.