Opisthonotal gland chemistry of a middle-derivative oribatid mite, Archegozetes longisetosus (Acari: Trhypochthoniidae)

Abstract

Opisthonotal glands of sarcoptiform mites secrete a variety of compounds known to have defensive and pheromonal functions. We studied the gland chemistry of cultured individuals of the desmonomatan oribatid mite Archegozetes longisetosus Aoki (Trhypochthoniidae), to compare it with that of other oribatid mites and to examine in a preliminary way how the molting process may affect it. GC-MS analysis of hexane extracts of adult mites revealed three monoterpenes (geranial, neral, neryl formate), two aromatic compounds [γ-acaridial (3-hydroxybenzene-1,2-dicarbaldehyde) and 2,6-HMBD (2-hydroxy-6-methylbenzaldehyde)] and four hydrocarbons (pentadecane, pentadecene, heptadecene and heptadecadiene). In decreasing order, the most abundant compounds were γ-acaridial, neral, neryl formate and 2,6-HMBD, with the other five present only in minor or trace amounts. Active proto-, deuto- and tritonymphs have chemical profiles similar to that of adult mites. The same profile results when extracted nymphs are early in the pharate stage of molting, but probably they lose the ability to secrete as the molt progresses. Gland reservoirs from molted exuviae contain a similar secretion, which proves the origin of the hexane extracts. In larvae, and in adults disturbed for 30 min, neryl formate was usually the major compound detected. None of these compounds are unique among Trhypochthoniidae, and most are common in Astigmata, but the overall profile distinguishes A. longisetosus from other studied species.