Social wasp parasites affect the nestmate recognition abilities of their hosts (<Emphasis Type="Italic">Polistes atrimandibularis</Emphasis> and <Emphasis Type="Italic">P. biglumis</Emphasis>, Hymenoptera,Vespidae)

Summary. Queens of the parasitic social wasp, Polistes atrimandibularis, temporarily mimic the odor of their host species, Polistes biglumis, but their offspring have parasite-specific odors. As a consequence, in parasitized colonies individuals with different odors co-inhabit the colony and host workers, who are responsible for colony defense, accept wasps with different odors. In order to verify whether this particular condition causes a change in recognition abilities of hosts, we tested nestmate/non-nestmate discrimination in field colonies invaded by social parasites (and in non-parasitized colonies as controls). Results show that parasitized colonies distinguish between nestmates and non-nestmates, distinguish their parasite queen from those that usurped alien colonies, and accept their parasite's non-mimetic offspring but make more recognition errors than non-parasitized colonies. The optimal acceptance threshold model predicts that when the frequency of encountering non-kin increases, residents become less permissive towards intruders. However, my data show that parasitized colonies are more permissive towards non-nestmates with respect to non-parasitized colonies but they are also more aggressive towards nestmates, suggesting that host workers' learning abilities are impaired.