Identification of larval caste and the regulation of queen development in colonies of the ant Harpegnathos saltator

A defining characteristic of eusocial insect societies is a reproductive division of labor between the queen and worker castes. This switch is generally regulated through control over larval nutrition; however, in ant species that are specialized predators, larvae feed independently in the nest, and fine control over larval nutrition may not be feasible. In one such species, Harpegnathos saltator, we have discovered that workers use an alternative means to regulate larval development: larval-directed biting. Workers of H. saltator bite queen-destined larvae to inhibit queen development during periods of the year when they are not producing sexuals, and this biting redirects larval development towards the worker phenotype. In order for workers to successfully inhibit queen development, workers must have a reliable method to identify queen-destined larvae. Our investigations have revealed a non-polar compound on the surface of queen-destined larvae that workers use to distinguish between castes. In general, larval pheromones in ants have proven illusive. This has led some to speculate that conflict between selfish larval interests and the interests of the colony has selected against cues that distinguish larvae by sex or caste. Our results support an alternative hypothesis.