Submitted to: Silverleaf Whitefly Research, Action and Technology Transfer Plan
Publication Type: Abstract Only
Publication Acceptance Date: March 27, 2002
Publication Date: February 26, 2002
Citation: Buckner, J.S., Hagen, M.M. 2002. The fatty acid composition of the internal lipids from silverleaf whitefly nymphs and adults [abstract]. Silverleaf Whitefly Research, Action and Technology Transfer Plan. p. 59. Technical Abstract: The cuticular lipids of Bemisia argentifolii Bellows and Perring (Homoptera: Aleyrodidae) nymphs (1) and adults (2, 3) have been characterized, but the identification and quantification of the internal lipids of whiteflies have not been determined. The assessment of the internal lipids as a source of nutrient reward is especially relevant to specific parasitoids of whiteflies since they consume their host from within. The identification and composition of the fatty acids associated with the major lipid classes (triacylglycerols, free fatty acids and phospholipids) within B. argentifolii nymphs were determined. Comparisons were made to the fatty acids present in the internal lipids of adult B. argentifolii. Feeding silverleaf whitefly nymphs were raised on young cantaloupe plants and adult whiteflies were maintained on hibiscus. Groups of 200-300 third and fourth instar nymphs were carefully removed from leaves, placed in glass vials, and their surface lipids were removed and discarded using hexane. The surface lipids from groups of pre-chilled adults were also removed with hexane. The internal lipids were then extracted by sonication for 45 min in 7-8 ml of chloroform/MeOH (2:1). The chloroform/MeOH homogenate was filtered through glass wool and partitioned twice between chloroform and water. The internal lipids of whiteflies were separated into neutral lipids, free fatty acids and phospholipids using a column of 80 - 180 mg of Porasil Prep silica (Waters Corp., Milford, MA). The separation was achieved using a modification of a novel solvent system containing tertiarybutylmethylether (t-BME) (4). Lipid samples were applied to the column in hexane and lipid fractions eluted using the following solvents: hydrocarbons, wax esters, aldehydes (99.5:0.5 hexane/t-BME); triacylglycerols (TAG), alcohols (96:4 hexane/t-BME); free fatty acids (FFA) (100:2 hexane/acetic acid); phosphatidylethanolamine (PE) (20:4:1 t-BME/MeOH/0.001M ammonium acetate, pH 8.6) and phosphatidylcholine (PC) (5:4:1 t-BME/MeOH/0.001M ammonium acetate, pH 8.6). The purity of lipid fractions was verified by silica HPTLC. Fatty acid methyl esters (FAME) were formed by alkaline hydrolysis of the triacylglycerol and phospholipid fractions followed by treatment of the free fatty acids with methanolic HCl. The FAME derivatives of fatty acids were separated by capillary gas chromatography (CGC) and analyzed using splitless injection at 200°C, a Supelco SP-2380 capillary column (30m x 0.25mm id.) in a Hewlett-Packard Model 5890 GC. The quantities of FAME were determined by converting integrated peak area data from the FID response using nonlinear regression slope data for increasing amounts (0.78-200 ng) of the authentic methyl esters of 14:0, 16:0, 16:1, 18:0, 18:1, 18:2, 18:3 and 20:0 fatty acids. All lipid classes contained variable distributions of 8 fatty acids: the saturated fatty acids, myristic acid (14:0), palmitic acid (16:0), stearic acid (18:0), arachidonic acid (20:0); the monounsaturated fatty acids, palmitoleic acid (16:1), oleic acid (18:1); the polyunsaturated fatty acids, linoleic acid (18:2), linolenic acid (18:3). Fourth instar nymphs had 5-10 times the quantities of fatty acids as compared to third instar nymphs and 1-3 times the quantities from adults. The quantity differences of fatty acids between fourth and third instar nymphs related to their size and weight differences: fresh weights of 19-28 mg/nymph and 5-9 mg/nymph, respectively. For nymphs and adults, TAG lipids were the major source of fatty acids, with oleic (18:1) and palmitic (16:0) acids as major components. For nymphs and adults, the majority of the polyunsaturated fatty acids, linoleic (18:2) and linolenic (18:3) were present in the phospholipid fractions (PE + PC).