Submitted to: International Society of Chemical Ecology Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 5/30/2002
Publication Date: N/A
Technical Abstract: The adult beetles, Aphthona lacertosa and Aphthona nigriscutis, used as biocontrol agents for leafy spurge, had a complex mixture of hydrocarbons on their cuticular surface consisting of alkanes, methylalkanes, alkenes and alkadienes as determined by gas chromatography-mass spectrometry. A trace amount of wax esters were present. In both species, the hydrocarbons were the major cuticular lipid class and the gas chromatographic profiles of the total hydrocarbons were similar. However, the profiles for the saturated hydrocarbon fraction were distinct for each species. Alkanes (n-alkanes and methyl-branched alkanes), alkenes and alkadienes comprised 26%, 44% and 30%, respectively, for A. lacertosa, and 48%, 26% and 26%, respectively, for A. nigriscutis, of the total hydrocarbons. The major methyl-branched hydrocarbons were 2-methylalkanes: 2-methyloctacosane and 2-methyltriacontane. The major monoene was hentriacontene and the major diene was tritriacontadiene. The species were unique in that a number of di- and tri-methyl-branched alkanes were present in minor quantities in which the first methyl branch was on carbon 2 or 3. Examples of structures were 2,10-and 2,12-dimethylalkanes, 2,6- and 2,4-, and 3,7-dimethylalkanes. 2,10,12-Trimethylalkanes with one methylene between adjacent methyl branch points were identified. The adjacent methyl branch points appear to cause an additional fragmentation in their mass spectra. Methylalkanes with an odd number of carbons in the backbone of the molecule were identified as 2,23-dimethylnonacosane and 2,25-dimethylhentriacontane; their mass spectra also corresponded to mass spectra for a 2,6 branching sequence. However, a 2,6 branching sequence is not biosynthetically feasible because such a structure has a straight-chain tail with an odd number of carbon atoms beyond the last methyl branch point. The 2,23 and 2,25 branching sequences could be synthesized starting with a primer derived from the amino acid leucine.