Karen Hicks

Quinones and phenols in the defensive secretions of neotropical opilionids

Three quinones (2,3-dimethyl-1,4-benzoquinone; 2,5-dimethyl 1,4-benzoquinone; and 2,3,5-trimethyl-1,4-benzoquinone) and two phenols (2,3-dimethylphenol and 2-methyl-5-ethylphenol) were isolated from the defensive secretions of four species of opilionids (suborder Laniatores) from the Canal Zone. Phenols had not previously been reported from opilionids, and 2-methyl-5-ethylphenol was not known as a natural product. The secretions, which are mixed with regurgitated enteric fluid upon discharge, are administered by the animals by leg dabbing.

Chemical defense of a rove beetle (Creophilus maxillosus).

The abdominal defensive glands ofC. maxillosus secrete a mixture (70μg/beetle) of isoamyl alcohol (I), isoamyl acetate (II), iridodial (III), actinidine (IV), dihydronepetalactone (VE), and (E)-8-oxocitronellyl acetate (X). When disturbed, the beetle everts the glands and revolves the abdomen so as to wipe the glands against the offending agent. Fecal fluid is commonly emitted at the same time and may become added to the glandular material. Ants (Formica exsectoides) are effectively fended off by the beetle and were shown in bioassays (Monomorium destructor) to be repelled by the four major components of the secretion (II, III, X, VE); the principal component (VE) was the most active. Some anatomical features of the glands are described.

Defensive steroids from a carrion beetle (Silpha americana)

The defensive anal effluent discharged bySilpha americana in response to disturbance contains a mixture of steroids stemming from a glandular annex of the rectum. The compounds have been characterized as 15β-hydroxyprogesterone (1, principal component), 5β-pregnan-15β-ol-3, 20-dione (2), 5β-pregnan-3α, 15β-diol-20-one (3), 5β-pregnan-7β, 15β-diol-3,20-dione (4), 5β-pregnan-3α, 7β, 15β-triol-20-one (5), 5β-pregnan-16α-ol-3,20-dione (6), and 5β-pregnan-3α, 16α-diol-20-one (7), none previously found in insects. Bioassays with jumping spiders showed compounds1 and6 to be feeding deterrents at the 1 μg level.

Naphthoquinones in defensive secretion of an opilionid

The defensive secretion of the opilionidPhalangium opilio contains 1,4-naphthoquinone and 6-methyl-1,4-naphthoquinone. Naphthoquinones are of rate occurrence in arthropods, having previously been reported only from certain tenebrionid beetles.