Submitted to: Silverleaf Whitefly Research, Action and Technology Transfer Plan
Publication Type: Abstract only
Publication Acceptance Date: 3/25/2002
Publication Date: 2/26/2002
Citation: Buckner, J.S., Jones, W.A. 2002. Methyl-branched alkanes as possible marking pheromones for female Eretmocerus mundus, a parasitoid of Bemisia argentifolii [abstract]. Silverleaf Whitefly Research, Action and Technology Transfer Plan. p. 158. Interpretive Summary:
Technical Abstract: Previous studies with Bemisia argentifolii Bellows and Perring (Homoptera: Aleyrodidae) nymphs have shown that wax esters were the major components of the cuticular lipids with lesser amounts of hydrocarbons, long-chain aldehydes and long-chain alcohols (1). The hydrocarbon fraction was identified as a homologous series of odd-carbon-number n-alkanes, C31 (40%), C33 (31%), C35 (18%) and C29 (11%) and trace amounts of even-carbon-number n-alkanes (C28-C34). In a more recent study, the cuticular lipids from B. argentifolii nymphs parasitized by the whitefly parasitoid Eretmocerus mundus Mercet contained measurable quantities of two additional components in their hydrocarbon fraction (2). Capillary gas chromatography (CGC) and CGC-mass spectrometry (CGC-MS) analyses and comparisons with an authentic standard indicated that the two hydrocarbons were the monomethyl-branched alkanes, 2-methyltriacontane (31 carbons) and 2-methyldotriacontane (33 carbons). In parallel experiments, no appreciable changes in lipid composition were observed for the cuticular lipids of whiteflies parasitized by another parasitoid, Encarsia pergandiella. In contrast to Encarsia spp., Eretmocerus spp. oviposit externally (under the nymph), yet still readily avoid superparasitism suggesting that an external discrimination cue must be present (2). Previous behavioral observations with E. mundus showed that, following oviposition, females often make apparent "host marking movements" that may leave a chemical that enables the searching female to distinguish parasitized from unparasitized hosts (3). Those comparative findings suggest a possible function of 2-methylalkanes as marking pheromones for ovipositing female E. mundus. The following set of experiments decreased the possibility that the extra 2-methylalkanes on cuticular surfaces of E. mundus-parasitized nymphs arose from biosynthesis and surface deposition during growth and development of the parasitoid, and supported the possibility for transfer of these compounds onto the surface of the host (nymphs) by searching/ovipositing E. mundus females. B. argentifolii nymphs were exposed to E. mundus females for approximately 8 hr and then removed from leaves after 48 hr. Only those nymphs with visible signs of an oviposited egg beneath each nymph were removed and pooled for subsequent analysis of their cuticular lipids. The hydrocarbon fraction of nymph samples that had been exposed to ovipositing E. mundus females showed the same 2-methylalkanes that were also present on those parasitized B. argentifolii nymphs that had been held 10 days after exposure to E. mundus females. In addition to 2-methylalkanes, small quantities of 31- and 33-carbon dimethyl-branched-alkanes were also identified in the hydrocarbon fraction from those nymphs exposed to E. mundus for 48 hr. Preliminary CGC-MS analyses of the cuticular lipids from E. mundus females have revealed major quantities of the same 2-methylalkanes and dimethyl-branched-alkanes that were on the cuticular surfaces of E. mundus-exposed B. argentifolii nymphs. These findings clearly demonstrate that the origin of the 'extra lipids' on the surfaces of E. mundus-parasitized nymphs is from the ovipositing female and that these lipids could be playing a role as host marking chemicals. Current studies are focused on defining the process for transfer of these methyl-branched lipids from the ovipositing parasitoid to its host.