ABSTRACT
The chemistry of the lemon-scented oil gland secretion of Collohmannia gigantea, a middle-derivative mixonomatan oribatid mite, was investigated by gas chromatography - mass spectrometry. Gas chromatographic profiles of whole body extracts of C. gigantea revealed two distinct chromatographic zones, the first containing a set of six volatile compounds, comprising the lemon-scented monoterpene aldehydes neral and geranial, the scented monoterpene ester neryl formate, a distinctly scented aromatic aldehyde (2-hydroxy-6-methyl-benzaldehyde = 2,6-HMBD), and the two non-scented hydrocarbons, tridecane and pentadecane. All six components appeared to be present in steady relative proportions in scenting mites only, indicating their unity within the scented secretion. In contrast, the components of the second chromatographic zone were less volatile and found in both, scenting and nonscenting mites. Chemically, they represent a set of fatty acids of already known cuticular origin. The secretion bouquet of the first chromatographic zone was linked with oil glands by histochemical means: large amounts of aldehydes were present only in oil gland reservoirs, not in any other region of the mite body. While chemical profiles of oil gland secretions of several dozen astigmatid mites are known, only one other oribatid oil gland composition, from a desmonomatan species, has been elucidated, being almost the same as that of C. gigantea. Moreover, all components of these two secretions are widely distributed amongst astigmatid mite species and may also be common in a restricted set of middle-derivative oribatids. These findings are consistent with the idea of astigmatid mite origin from a mixonomatan-desmonomatan group.
