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United States Department of Agriculture

Agricultural Research Service

Title: Transfer of Methyl-Branched Hydrocarbons from the Parasitoid, Eretmocerus Mundus, to Silverleaf Whitefly Nymphs During Oviposition

Authors
item Buckner, James
item Jones, Walker

Submitted to: Comparative Biochemistry and Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 1, 2004
Publication Date: January 1, 2005
Citation: Buckner, J.S., Jones, W.A. 2005. Transfer of methyl-branched hydrocarbons from the parasitoid, Eretmocerus mundus, to silverleaf whitefly nymphs during oviposition. Comparative Biochemistry and Physiology A. 140(1):59-65.

Interpretive Summary: The silverleaf whitefly, Bemisia argentifolii, has been 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. One of the most important natural enemies of whiteflies is the parasitic wasp, Eretmocerus mundus, and female wasps deposit their eggs beneath whitefly nymphs and not within them. Experiments were designed to determine whether ovipositing E. mundus females mark their nymphal host with recognition chemicals to enable searching females to discriminate parasitized from unparasitized hosts. Three experimental groups of B. argentifolii nymphs were collected and their cuticular lipids comparatively analyzed by gas chromatography-mass spectrometry. Parasitoid-exposed groups were designated as those nymphs that had an egg beneath them. Also collected were control treatment nymphs: nymphs not exposed to E. mundus and a third treatment condition of parasitized B. argentifolii nymphs that had been held 10 days after interaction with E. mundus females. Comparative chromatographic analyses indicated the presence of quantities of C31 and C33 dimethylalkanes only in the parasitoid-exposed groups of treated nymphs and not in the extracts from control nymphs and the parasitized nymphs that had undergone one or more nymphal molts. Furthermore, as a potential source for these marking lipids, the C31 and C33 dimethylalkanes were shown to be major lipid components of the hexane extracts from E. mundus females.

Technical Abstract: The parasitic wasp Eretmocerus mundus is a natural enemy of whiteflies. Female E. mundus deposit eggs beneath whitefly nymphs and not within them. Experiments were designed to determine whether ovipositing E. mundus females mark their nymphal host with recognition chemicals to enable searching females to discriminate parasitized from unparasitized hosts. Nymphs of the silverleaf whitefly Bemisia argentifolii that had interacted with ovipositing female wasps and had a parasitoid egg beneath them were collected from leaves and designated as parasitoid-exposed. Also collected were control treatment nymphs that were not exposed to E. mundus, and a third treatment condition of parasitized B. argentifolii nymphs that had been held 10 days after exposure to female wasps. Lipids were removed from the cuticular surfaces of the various treatment groups of B. argentifolii nymphs with hexane and the lipid components in the hexane extracts were characterized and quantified by gas chromatography-flame ionization detection and gas chromatography-mass spectrometry. Comparative chromatographic analyses indicated the presence of quantities of C31 and C33 dimethylalkanes only in the parasitoid-exposed groups of treated nymphs and not in the extracts from control nymphs or the parasitized nymphs that had been held 10 days after exposure. Furthermore, the C31 and C33 dimethylalkanes were shown to be major lipid components of the hexane extracts from E. mundus females. Since the cuticular lipids were removed from parasitoid-exposed nymphs before interaction with hatched parasitoid larvae, the findings indicated that the dimethylalkanes were transferred onto nymphal cuticles by ovipositing E. mundus females.

Last Modified: 7/22/2014