In eusocial Hymenoptera, workers usually cannot mate but can lay male-destined haploid eggs. In contrast, in many species, worker reproduction is regulated by means of worker policing, which consists of two behavioral categories: aggression towards workers that have developed ovaries, and the destruction of worker-laid eggs. We focused on the latter behavior in the ant Diacamma sp. from Japan, in which a mated worker (gamergate) serves as the functional queen in each colony. An experiment in which we introduced both worker-laid eggs and gamergate-laid eggs from foreign colonies showed that workers preferentially destroyed the workerlaid eggs. This indicates that workers can discriminate workerlaid eggs from gamergate-laid eggs. In contrast, gamergates destroyed all introduced eggs that they discovered. Our chemical analysis of egg surface substances revealed that the worker-laid eggs clearly differed from gamergate-laid eggs in their surface hydrocarbons (SHCs), with the former containing more long-chain components. However, a bioassay to test whether specific components of the SHCs trigger the observed discrimination behavior by workers remains to be done.

In eusocial Hymenoptera, information on the presence of a queen is considered to play an important role in regulating worker reproduction. We examined the mode of transmission of this putative queen information to workers. Previous studies have reported that, in Diacamma sp. from Japan, unmated helper workers perceive the presence of a gamergate (functional queen) only through direct physical contact with her. In contrary to this conclusion, we showed, by an experiment that exposed workers either to the gamergate or to the eggs laid by the gamergate, that the presence of eggs laid by the gamergate to some extent suppressed the workers' dominance interaction, a behavior that is associated with self-reproduction by unmated workers. We discuss the relative importance of direct and indirect transmission of gamergate-presence information under natural conditions in this ant.

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