Submitted to: Journal of Insect Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 6, 2010
Publication Date: N/A
Interpretive Summary: The sweet potato whitefly can attack more than 600 species of plants, causing billions in crop losses annually. Heavy application of pesticides to control sweet potato whitefly has led to the development of pesticide resistance and has caused the decline of whitefly natural enemies. Therefore, finding environmentally friendly biological agents for farmers and greenhouse growers to use to cost-effectively control the sweet potato whitefly is a top priority. Results from experiments designed to develop improved artificial diets for sweet potato whitefly revealed that some simple sugars had an insecticidal effect on this whitefly. Therefore, experiments were conducted to evaluate the effects of 15 selected sugars for toxicity against the sweet potato whitefly. Four of these sugars were found to prevent immature whiteflies from maturing. The lifespan of the adult whitefly was also found to be shortened by these and other sugars. Many of these sugars are found naturally in plants, so this information will be of interest to scientists and plant breeders developing whitefly resistant plants.
Technical Abstract: The effects of 15 sugars on sweet potato whitefly (Bemisia tabaci) survival were determined using bioassays. Arabinose, mannose, ribose and xylose were strongly inhibitory to both nymphal and adult survival. When 10% mannose was added to the diet, 10.5%, 1.0% and 0% of nymphs developed to the 2nd, 3rd and 4th instars, respectively. When 10% arabinose was added, 10.8% and 0% of the nymphs molted to the 2nd and 3rd instars, respectively. Addition of 10% xylose or ribose completely terminated whitefly development, preventing the molt to the 2nd instar. In tests using whitefly adults, arabinose, inositol, lactose, maltose, mannitol, mannose, melibiose, ribose, sorbitol, trehalose and xylose significantly reduced mean day survival. Mortality rates were highest when arabinose, mannitol, mannose, ribose or xylose was added to the diet. Mode of action studies revealed that toxicity was not due to the inhibition of alpha glucosidase (converts sucrose to glucose and fructose) and/or trehalulose synthase (converts sucrose to trehalulose) activity. The result of agarose gel electrophoresis of RT-PCR products of bacterial endosymbionts amplified from RNA isolated from whiteflies fed with 10% arabinose, mannose or xylose indicated that the concentration of endosymbionts in sweet potato whitefly mycetomes were not affected by the toxic sugars. In experiments in which whiteflies were fed on diets that contained radiolabeled sucrose, methionine or inulin and one or none (control) of the highly toxic sugars, radioactivity (expressed in DPM) in the whitefly body, in excreted honeydew and/or carbon dioxide was significantly reduced as compared to controls. Thus, it appears that the ability of insecticidal sugars to act as antifeedants is responsible for their toxicity to B. tabaci.