Cuticular hydrocarbons of Tribolium castaneum: Effects of the food additive tricalcium phosphate

Abstract

Two groups of hydrocarbons were isolated from surface extracts of adults of the red flour beetle, Tribolium castaneum (Herbst). A group of seven unsaturated hydrocarbons with chain lengths of C 14 to C 17 associated with the defence glands of this species was identified using gas chromatography and gas chromatographny-mass spectrometry. The principal component was identified as 1-pentadecene which amounted to 75% of the unsaturated fraction. Two alkadienes, pentadeca-1,6-diene and heptadeca-1,8-diene, were also identified. Normal and branched-chain alkanes associated with the cuticular lipids constituted the higher boiling components whose equivalent chain lengths ranged from C 25C 35. n- Heptacosane and n- nonacosane were the predominant n- alkanes . There were two main mixtures of branched-chain alkanes with equivalent chain lengths of C 27.4 (11-and 13-methylheptacosanes) and C 27.7 (11,15-dimethylheptacosane and 3-methylheptacosane). When tricalcium phosphate (TCP) was used as a 24-hr contact desiccant dust on adults, the unsaturated hydrocarbon fraction was significantly reduced, apparently as a result of direct absorption by the TCP. The saturated branched alkanes at C 27.4 and C 27.7 were also significantly reduced. When TCP was incorporated as a nutrient in wheat-soy blend, desiccation of T. castaneum also occurred and the unsaturated hydrocarbon fraction was reduced by 74%; however, the saturated fraction, particularly n- heptacosane , had a significant increase. Desiccation itself did not alter the ratio of cuticular hydrocarbons, indicating that dietary TCP somehow causes the observed changes either through direct contact or some metabolic aberration.