Submitted to: Comparative Biochemistry and Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 29, 2002
Publication Date: March 12, 2003
Citation: NELSON, D.R., ADAMS, T.S., FATLAND, C.L. HYDROCARBONS IN SURFACE WAX OF EGGS AND ADULTS OF THE COLORADO POTATO BEETLE, LEPTINOTARSA DECEMLINEATA. COMPARATIVE BIOCHEMISTRY AND PHYSIOLOGY. Part B 134(3):447-466. 2003. Interpretive Summary: The Colorado potato beetle, a pest of potato world-wide, can also be a pest of tomato, egg plant and pepper. The surface chemistry of this insect is somewhat unusual in that only trace amounts of straight-chain alkanes are present and that the majority of the methyl-branched alkanes have a methyl group on the second carbon of the chain. This fact is significant because the biosynthesis of these molecules needs a methyl-branched amino acid, either leucine or valine as a precursor. If the carbon-chain backbone of the molecule is an even number of carbons, the precursor is valine; if an odd number of carbons the precursor is leucine. Generally, it is assumed in assigning positions to other methyl branches that there will be an odd number of carbons between the methyl branch on carbon 2 and the next methyl branch. This assumption is usually valid because the major components in the surface chemicals have an even number of carbons in the straight-chain portion of the molecule. However, we identified minor components with an odd number of carbons in the straight-chain portion of the molecule. If a structure is proposed with an odd number of carbons between the methyl branch on carbon 2 and the next methyl branch, the proposed structure has an odd number of carbons beyond the last methyl branch. Based on current concepts of biosynthesis, there can not be an odd number of carbons beyond the last methyl branch. We showed that methyl-branched alkanes with an odd number of carbons in the straight-chain portion of the molecule can have an even number of carbons between the methyl branches and that such a structure now has an even number of carbons after the last methyl branch. We showed that such structures meet 3 criteria which we had earlier promulgated: 1.) the structure must have the expected gas chromatographic retention times; 2.) it must have the expected mass spectrum; and 3.) it must be biosynthetically feasible.
Technical Abstract: Only trace amounts of n-alkanes and alkenes were detected in the surface hydrocarbons of adult males and females, larvae and eggs, of the Colorado potato beetle. The major components of the egg hydrocarbons were dimethylalkanes (40%) and trimethylalkanes (24%) in which the first methyl branch was on carbon 2. The major dimethylalkanes were an approximately 2:1 mixture of 2,10- and 2,6-dimethyloctacosanes in females and eggs. The major trimethylalkanes were a mixture of 2,10,16- and 2,10,18-trimethyloctacosanes. 2,x- and 2,x,y-methyl-branched alkanes with an odd-numbered carbon backbone were proposed to have an even number of carbons between the first and second methyl branch points indicating that their biosynthesis started with a primer derived from leucine. 13,17,21,25-Tetramethylheptatriacontane was the only tetramethylalkane identified. Females and eggs had more hydrocarbons with a 2-methyl branch point than did the males. The eggs had the lowest amount of internally-branched dimethylalkanes but the largest amount 2,x-dimethylalkanes in their surface hydrocarbons.