Submitted to: Archives of Insect Biochemistry and Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 30, 2002
Publication Date: N/A
Interpretive Summary: The silverleaf whitefly (SLWF) causes more than 500 hundred million dollars in crop losses each year by feeding on plant fluids, transmitting pathogenic viruses, and producing honeydew, a substance that supports the growth of sooty mold. The development of pesticide resistance and concern for environmental safety have made the reduction of pesticide use a primary ygoal for agriculture and has resulted in Integrated Pest Management programs putting more emphasis on cost-effective biological control strategies and the use of biopesticides/insect growth regulators to prevent whitefly damage. The development of insect-specific biopesticides as well as the development of artificial rearing systems for natural enemies such as insect parasites requires information concerning the regulation of physiological processes in whiteflies, information which is seriously lacking. In these investigations, we use the staging system that we developed for the greenhouse whitefly (GHWF) to track development in SLWFs to describe structural changes that occur during SLWF adult development and to determine the concentration of molting hormones in developing last stage and adult whiteflies. A comparison of developmental rates, timing and progress of metamorphosis to the adult and accompanying changes in molting hormone concentration between the SLWF and the GHWF revealed that there were important differences between the two species. Information generated concerning the progress, nature and regulation of SLWF molting and metamorphosis should contribute to: 1)the development of new biopesticides and the determination of the mode of action of these control agents, and 2) the development of artificial diets to support the production of parasitic wasps that are natural enemies of the SLWF.
The developmental progress of SLWF (Bemisia argentifolii) third instars and fourth instar/pharate adults were monitored using a tracking system which had been designed to identify synchronous individuals in a related species of whitefly, the GHWF, Trialeurodes vaporariorum. When reared on green beans under conditions of LD 16:8 and a temperature of 26 plus or minus 2 degrees C, the body depth of third instar SLWFs increased from approximately 0.04 mm (Stage 2) to 0.175 - 0.2 mm (Stage 7-8) and the body depth of the fourth instar increased from approximately 0.1 mm (Stage 1) to 0.25-0.30 mm (Stage 4-5). The durations of the third instar and the fourth instar/pharate adult were approximately three and seven days, respectively. Examination of horizontal sections of fourth instars revealed that adult eye and wing development are initiated during Stage 6, the stage in which an external examination showed that the eye has begun to undergo pigment diffusion. Ecdysteroid titers peaked at approximately 400 fg/ug protein during stages four through 6A of the fourth instar, i.e., just prior to and upon the initiation of the pharate adult stage. Although adult development is initiated later in the SLWF than in the GHWF, the same rapidity of metamorphosis is observed in both species. Within approximately 24 h, the simple bi-layered wing bud developed into a deeply folded wing of nearly adult proportions and within an additional 12 - 24 h, the nymphal eye and wing bud had been replaced by the well-differentiated eye and wing of the adult whitefly. Our study is the first to describe the regulation, timing, and progress of the nymphal - adult molt and of the structural changes that accompany nymphal-adult metamorphosis in the SLWF.