Submitted to: Journal of Insect Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/17/2001
Publication Date: N/A
Interpretive Summary: Whiteflies attack more than 500 species of food, fiber and ornamental plants causing crop losses that total hundreds of millions of dollars. Concern about the development of pesticide resistance in whiteflies as well as the need to reduce pesticide usage because of environmental considerations has resulted in increased emphasis on the use of cost-effective biological control strategies in IPM programs. These includ the enhanced use of natural enemies such as parasitic wasps and the development of environmentally safe biopesticides that interfere with whitefly growth and function. However, although there is a growing body of literature concerning the biology of whiteflies and the physiology of feeding, little information is available concerning the regulation of development, information that is essential to the enhancement of existing, as well as the development of new biological control technology. In this work, we present a precise staging system for identifying physiologically synchronous whiteflies, describe the internal and external structural changes that accompany the molt from the nymph to the adult and determine the changes in molting hormone titer that occur during maturation. Now available, is a useful system of markers for tracking whitefly development and marking important physiological events in the whitefly life cycle. Results clarify the mechanism by which molting and metamorphosis are controlled. Information generated should be useful to other scientists whose focus is the discovery of new biopesticides and the mode of action of these control agents as well as the artificial production of large numbers of natural enemies to control whitefly damage.
Technical Abstract: A system of markers has been devised to track the development of 3rd and 4th instar/pharate adult greenhouse whiteflies (GHWFs). Based on measurements of body width and body length. The product of the two measurements was useful in distinguishing between instars. Body depth was used to divide the 3rd instar into eight stages. Body depth and color, appearance of the developing adult eye were used to divide the 4th instar/pharate adult into 9 stages. When expressed as fg/whitefly, ecdysteroid titers peaked in Stage-4 3rd instars (approx. 550 fg) and Stage 4/5 4th instars (approx. 300 fg). When expressed as fmg/microgram protein, ecdysteroid levels of 3rd instars were highest in Stages 1 and 2, decreased during Stages 3 and 4 and dropped to lower levels in Stages 5 and 6. Hormone levels of 4th instars/pharate adults were similar during Stages 1 - 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 the initiation of the molt to the pharate adult probably occurs in Stage-4 or -5 4th instars. Results from histological studies support this view. In Stage-4 nymphs, subtle changes observed in the eye's corneagenous cells indicated that adult eye development had been initiated. In a few Stage-4 and all Stage-5 nymphs, the early stages of wing development were evident. In stage-6 whiteflies, 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. Our study is the first to investigate the timing and regulation of the molt, ecdysteroid titers and the internal anatomical changes associated with metamorphosis in these insects.