Cuticular hydrocarbons of the dampwood termite, Zootermopsis nevadensis: Caste differences and role of lipophorin in transport of hydrocarbons and hydrocarbon metabolites

The epicuticular and internal hydrocarbons (HC) from different castes of th e dampwood termite Zootermopsis nevadensis were analyzed by gas chromatogra phy-mass spectrometry. The epicuticular HC profiles of workers and alates c ontained large proportions of n-heneicosane (n-C21), 5-methylheneicosane (5 -MeC21), and 5,17- and 5,15-dimethylheneicosane (5,17-, 5,15-diMeC21). Sixt y-three HC peaks were identified as normal-, monomethyl-, dimethyl-, and tr imethylalkanes up to 41 carbons long. The HC content of the internal tissue s was significantly greater than on the epicuticle in all castes examined ( 2.8-fold in female alates, 5.7-fold in male alates, and 13.7-fold in worker s). The hemolymph of all castes, including workers, soldiers, nymphs, and f emale and male alates, contained large amounts of HC and all hemolymph samp les had nearly identical HC profiles. However, the hemolymph profile was re markably different from the cuticular profile. KBr equilibrium gradient ult racentrifugation of worker hemolymph showed that all HC were associated wit h a high-density lipophorin (density of 1.12 +/- 0.005 g/ml) consisting of two subunits, apolipophorin-I (220 kDa) and apolipophorin-II (82 kDa). Afte r topical application of radiolabeled 3, 11-dimethylnonacosane, a HC that i s closely related to a native HC, all the internalized HC and radiolabeled lipid metabolites that were recovered from the hemolymph were associated wi th lipophorin. These findings are consistent with the hypothesis that lipop horin transports KC and some HC metabolites through the hemolymph from the sites of synthesis to the integument and from the integument to metabolic a nd excretory tissues. In many social insects. different castes have differe nt relative proportions of the same HC and Lipophorin appears to play an im portant role in regulation of the externalization and internalization of HC and, therefore, in the attainment of caste-specific chemical profiles.