Kin recognition in the larvae of a solitary insect: the cue is in the plug

The production of cues that indicate the identity of the sender represents an important aspect of recognition because it may mediate kin recognition and altruism. Although kin recognition cues have often been studied in social insects, only a few studies have reported kin recognition in solitary insects. Furthermore, contrary to cues used for parent--offspring recognition, cues involved in sibling recognition in solitary insects have received far less attention. Here we report that the solitary parasitoid larvae of a non--social insect, Aleochara bilineata Gyll (Coleoptera: Staphylinidae), use a chemical cue to recognize their sibs. This cue is present on the plug placed by resident larvae on the host puparium during the parasitization process. When plugs from sib larvae or unrelated larvae are placed on healthy hosts, larvae preferentially parasitize hosts bearing unrelated larvae plugs. When plugs are washed in hexane, larvae no longer display any preference between sib and unrelated larvae plugs. The extraction of the kin recognition chemicals is confirmed by the larval recognition of healthy hosts bearing a hexane extract of sib-parasitized pupae. This nonpolar chemical cue is short lived and is no longer recognized 24 h after having been deposited on the host puparium by larvae. The longevity of the cue used in kin recognition fits precisely the period when a larva may superparasitize a host. The adaptiveness of this cue and its potential source in the larvae are discussed. Copyright 2010, Oxford University Press.