Defensive glands in the adult and larval stages of the darkling beetle, Luprops tristis

Abstract

Invasion by large populations of the litter-dwelling darkling beetle Luprops tristis Fabricius (Coleoptera: Tenebrionidae) following the short spell of summer rains during April, and their extended state of dormancy is a regular event in rubber plantation habitats in south-western India. Strong smelling secretions of the beetle cause blisters on skin of human beings. Such secretions appear defensive because they appear to facilitate their avoidance by other predatory organisms. Defensive glands in the larvae and adults of L. tristis are described, as well as the mode of eversion of the glands. The glands in larvae consist of two pairs of noneversible glands in a conical depression on the 2(nd) and 3(rd) sternites, whereas in adults only one pair occurs between 7(th) and 8(th) sternal segments. These glands may be a major reason for avoidance of larvae and adults by their natural enemies and their very high numbers in the litter of rubber plantations.

Figure 1:

Line diagram of defensive gland of Luprops tristis. (a) Adult (dorsal view of the gland reservoirs cut from the remainder of the sternites); (b) Larva (view of paired glands of one side from the inside of the body and the reservoirs reflected to the exterior). High quality figures are available online.

Figure 2:

External view of defensive gland of Luprops tristis. (a) Adult; (b) lateral external swellings on sternite 2 and 3 of larva (paired swellings of one side). High quality figures are available online.