Submitted to: Archives of Insect Biochemistry and Physiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/20/2000
Publication Date: 6/1/2000
Citation: Buckner, J.S., Poprawski, T.J., Jones, W.A., Nelson, D.R. 2000. Effects of whitefly parasitoids on the cuticular lipid composition of Bemisia argentifolii (Homoptera: Aleyrodidae) nymphs. Archives of Insect Biochemistry and Physiology. 44(2):82-89. Interpretive Summary: The silverleaf whitefly, Bemisia argentifolii, has become a very serious pest of agricultural crops in the southern U.S., including cotton, and a wide range of ornamentals, melons and vegetables. Whitefly nymphs and adults damage crops by extracting large quantities of phloem sap that causes wilting and decreased plant development. Feeding whiteflies also excrete "sticky" honeydew that contaminates the surroundings and serves as a medium for sooty mold, and they serve as vectors to transmit yield-limiting viruses and other plant disorders. Studies have been conducted on the effective implementation of beneficial insect predators and parasitoids for biological control of whiteflies. Two of the most important natural enemies of whiteflies are the parasitic wasps, Eretmocerus mundus and Encarsia pergandiella. We conducted experiments to determine the parasitic effects of these two wasps on the composition of cuticular lipids of B. argentifolii nymphs. Analysis by capillary gas chromatography-mass spectrometry revealed that no appreciable changes in lipid composition were observed for E. pergandiella-parasitized nymphs as compared to unparisitized nymphs. However, the cuticular lipids of E. mundus-parasitized nymphs contained measurable quantities of two additional hydrocarbon components, the methyl-branched alkanes, 2-methyltriacontane and 2-methyldotriacontane. The occurrences and functions of 2-methylalkanes as cuticular lipid components of insects are discussed and specifically, in regard to host (whitefly) recognition, acceptance and discrimination by parasitoids.
Technical Abstract: Experiments were conducted to determine the effects of whitefly parasitoids on the cuticular lipid composition of silverleaf whitefly, Bemisia argentifolii Bellows and Perring [=sweetpotato whitefly, Bemisia tabaci (Gennadius), Biotype B] nymphs. The cuticular lipids of B. argentifolii nymphs that had been attacked by parasitic wasps, either Eretmocerus mundus Mercet or Encarsia pergandiella Howard, were characterized by capillary gas chromatography (CGC) and CGC-mass spectrometry (CGC-MS) and the results compared with the cuticular lipids of unparasitized nymphs. Previous studies with B. argentifolii nymphs had shown that wax esters were the major components of the cuticular lipids with lesser amounts of hydrocarbons, long-chain aldehydes and long-chain alcohols. No appreciable changes in lipid composition were observed for the cuticular lipids of E. pergandiella-parasitized nymphs as compared to unparasitized controls. However, the cuticular lipids from nymphs parasitized by E. mundus contained measurable quantities of two additional components in their hydrocarbon fraction. CGC-MS analyses and comparisons with an authentic standard indicated that the two hydrocarbons were the even-numbered chain length methyl-branched alkanes, 2-methyltriacontane and 2-methyldotriacontane. The occurrences and possible functions of 2-methylalkanes as cuticular lipid components of insects are discussed and specifically, in regard to host recognition, acceptance and discrimination by parasitoids.