|PATEL, SEJAL - MA INST TECHNOLOGY
|GIBBS, ALLEN - UNIV ARIZONA, TUCSON
Submitted to: Journal of Insect Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/4/2001
Publication Date: 4/24/2001
Interpretive Summary: A procedure was developed to measure the amount of wax ester isomers in mixtures of wax esters by gas chromatography-mass spectrometry. This procedure also enables the measurement of the amount of wax esters in the presence of laboratory contaminates, hydrocarbons and many other components that may be found on the cuticular surface of insects or other on organisms and which interfere or prevent analysis by other methods. We determined the physical characteristics of individual wax esters and also how the physical properties changed when the wax esters were present as mixtures or in association with hydrocarbons which is how they normally occur in nature. These findings allow some degree of predictability as to the waterproofing ability of the cuticular lipids under environmental conditions. The wax esters most typically found on the cuticle of terrestrial arthropods occur in a solid state under physiological conditions, thereby conferring greater waterproofing.
Technical Abstract: Wax esters are major constituents of the surface lipids in many terrestrial arthropods, but their study is complicated by their diversity. We developed a procedure for quantifying isomers of straight-chain saturated and unsaturated wax esters having the similar molecular weights in mixtures, using single-ion monitoring of the total ion current data from gas chromatography-mass spectrometry. We examined the biological consequences of structural differences by measuring the melting temperatures, Tm, of >60 synthetic waxes, containing 26-48 carbon atoms. Waxes containing saturated alcohol and acid moieties melted at 38-73 deg. C. The main factor affecting Tm was the total chain length of the wax ester, but the placement of the ester bond also affected Tm. Insertion of a double bond into either the alcohol or acid moiety decreased Tm by ~30 deg. C. Simple mixtures of wax esters with n-alkanes melted several deg. C lower than predicted from the melting points of the component lipids. Our results indicate that the wax esters of primary alcohols that are most typically found on the cuticle of terrestrial arthropods occur in a solid state under physiological conditions, thereby conferring greater waterproofing. Wax esters of secondary alcohols, which occur on melanopline grasshoppers, melted >60 deg. C below primary esters of the same molecular weight and reduced Tm of the total surface lipids to environmental values.