INVASION OF NESTS OF LASIOGLOSSUM-IMITATUM BY A SOCIAL PARASITE, PARALICTUS-ASTERIS (HYMENOPTERA, HALICTIDAE)

Paralictus asteris Mitchell is a socially parasitic sweat bee that inv ades nests and becomes the dominant reproductive in colonies of a phyl ogenetically related host, Lasioglossum (Dialictus) imitatum (Smith). The parasite has a greatly enlarged quadrate head, with elongate scyth e-like mandibles, and other morphological modifications apparently ass ociated with a parasitic lifestyle. Nevertheless, the parasite did not forcefully enter nests. Host guards adopted a defensive posture at th e nest entrance when they contacted a dead, frozen parasite, suggestin g that they recognized the intruders as parasites. Living parasites, h owever, only sometimes induced this guarding response, while in other cases parasites entered host nests without obvious signs of aggression from the guard. Guards also responded aggressively to both frozen and living conspecifics from other nests, but were not aggressive to livi ng or frozen nest-resident conspecifics, suggesting that the cues used for recognition of both unrelated conspecifics and parasites are chem ical ones. More than one parasite can invade and occupy a nest, and su ccessful invasion was not influenced by whether a parasitic female was mated or had developed ovaries.