Triacylglycerol and phospholipid fatty acids of the silverleaf whitefly: Composition and biosynthesis

Abstract

The identification and composition of the fatty acids of the major lipid classes (triacylglycerols and phospholipids) within Bemisia argentifolii Bellows and Perring (Homoptera: Aleyrodidae) nymphs were determined. Comparisons were made to fatty acids from the internal lipids of B. argentifolii adults. The fatty acids, as ester derivatives, were analyzed by capillary gas chromatography (CGC) and CGC-mass spectrometry (MS). All lipid classes contained variable distributions of eight fatty acids: the saturated fatty acids, myristic acid (14:0), palmitic acid (16:0), stearic acid (18:0), arachidic 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 fatty acid quantity differences between fourth and third instar nymphs were related to their size and weight differences. The percentage compositions for fatty acids from each lipid class were the same for the pooled groups of third and fourth instar nymphs. For nymphs and adults, triacylglycerols were the major source of fatty acids, with 18:1 and 16:0 acids as major components and the majority of the polyunsaturated fatty acids, 18:2 and 18:3 were present in the two phospholipid fractions, phosphatidylethanolamine and phosphatidylcholine. Evidence was obtained that whiteflies indeed synthesize linoleic acid and linolenic acid de novo: radiolabel from [2-(14)C] acetate was incorporated into 18:2 and 18:3 fatty acids of B. argentifolii adults and CGC-MS of pyrrolidide derivatives established double bonds in the Delta(9,12) and Delta(9,12,15) positions, respectively.

Characterization of triacylglycerols from overwintering prepupae of the alfalfa pollinator Megachile rotundata (Hymenoptera: Megachilidae)

“…Reaction with 10% HCl in MeOH was used to convert fatty acids to their methyl ester derivatives. The methods for hydrolysis and esterification to yield fatty acid methyl esters (FAME) have been previously described (Buckner and Hagen, 2003). Fatty acids were converted to their trimethysilyl derivatives by reaction with BSA.…”

“…After cooling, the sample was diluted 10-fold using BSA/DMF/ benzene (20:20:60) and portions analyzed by CGC-MS. For determination of double bond location for the fatty acids, the FAMEs from the TAG fraction were converted to their pyrrolidine derivatives. Methods for reaction of FAME with pyrrolidine and recovery of the fatty acid pyrrolidides were as previously described (Buckner and Hagen, 2003).…”

“…Operating conditions for the GC-MS analysis for lipid identification and methods for using authentic standards for determination of lipid quantities have been previously described (Buckner et al, 1999;Buckner and Hagen, 2003). Fatty acid pyrrolidides were analyzed using a Hewlett-Packard 5970 GC-MS equipped with a Supelco SP-2380 capillary column (30 m × 0.25 mm × 0.2 µm film thickness) and splitless injector at 260°C.…”

“…Helium flow rate was 1 ml/min. Mass spectra data were compared to the mass spectra of the fatty acid pyrrolidides of authentic standards as previously described (Buckner and Hagen, 2003).…”

“…The position of double bonds in the unsaturated fatty acids from TAG was determined by GC-MS analysis of their pyrrolidine derivatives as previously described (Buckner and Hagen, 2003). For the mass spectrum of an unsaturated component, if an interval of 12 atomic mass units is observed between the most intense peaks of clusters of fragments containing n and n-1 carbon atoms Archives of Insect Biochemistry and Physiology Fig.…”