|Blackburn, Michael - Mike|
Submitted to: Journal of Insect Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/20/2006
Publication Date: N/A
Interpretive Summary: The sweet potato whitefly (SPWF) and the greenhouse whitefly are tiny insects that attack many different kinds of plants in the field and in greenhouses. World-wide, whiteflies cause billions of dollars of damage in crop losses each year. Information concerning the regulation of physiological/biochemical processes in whiteflies is seriously lacking. In this paper, we present new data concerning an insect hormone, juvenile hormone, that regulates many different insect life functions. We found that the whitefly juvenile hormone is JH-III, the most common juvenile hormone of insects. We detected it in SPWF eggs and young nymphs. In SPWF eggs, JH levels were approximately 10 times greater in 2-3 day-old eggs than in 5 day-old eggs. It is probable that the relatively high level of JH in Day 2-3 eggs is associated with the differentiation of various whitefly tissues during egg development. This information should be useful to scientists and pest managers who want to develop new strategies of insect control based on altering or inhibiting whitefly hormones.
Technical Abstract: Ecdysteroids and juvenile hormones (JHs) regulate many physiological events throughout the insect life cycle, including molting, metamorphosis, ecdysis, diapause, reproduction and behavior. Fluctuation of whitefly ecdysteroid levels and the identity of the whitefly molting hormone have only been reported within the last few years. An ecdysteroid commitment peak that is associated with the reprogramming of tissues for a metamorphic molt in many insect species was not observed in either sweet potato whitefly, Bemisia tabaci (Biotype B), or greenhouse whitefly, T. vaporariorum, last nymphal instars. Ecdysteroids reach peak levels prior to the initiation of the nymphal-adult metamorphic molt. Adult eye and wing differentiation begin earlier (Stages 4 and 5) in the 4th instar greenhouse whitefly than in the sweet potato whitefly (Stage 6), and the premolt peak is 3 – 4 times greater in B. tabaci (~400 fg/µg protein) than in T. vaporariorum (~120 fg/µg protein). The JH of B. tabaci nymphs and eggs was found to be JH-III supporting the view that JH-I and JH-II are only present in lepidopteran insects. In B. tabaci eggs, JH levels were approximately 10 times greater on day 2/3 (0.44 fg/egg) than on Day 5 (0.04 fg/egg) post-oviposition. Approximately 1.4 fg/2nd-3rd instar nymph was detected. It is probable that the relatively high level of JH in Day 2/3 eggs is associated with the differentiation of various whitefly tissues during egg development.