文摘
The role of queens in caste regulation of pharaoh ant colonies has been puzzling biologists for decades. Worker-fertility-inhibiting pheromones are lacking, as workers of this polygynous species are completely sterile. Yet, fertile queens possess inhibiting powers over the production of new gynes and males. Here we test whether queen-produced cuticular compounds or factors related to eggs affect sexual brood survival. Additionally, the influence of dead queens and virgin queens is investigated. Hereto, subcolonies consisting of workers, mixed worker brood and sexual larvae are treated with eggs, living queens, dead queens, virgin queens or queen extracts. The extracts are prepared with (phosphate-buffered saline), hexane or acetone and applied on either glass dummies (chemical cue only) or queen dummies (visual and chemical cue). Subsequently, the number of surviving larvae and their sex ratio are recorded. Only treatments containing living queens show a significant drop in eclosing sexual larvae. In all other treatments the survival of sexual larvae is unaffected. Several hypotheses are discussed involving competition for ‘royal’ food between queens and sexual larvae, food deprival of sexual larvae by workers or cannibalism of sexual brood by queens and/or workers. Although brood cannibalism seems the most valid explanation, as it allows recycling the energy used for brood production throughout the colony, our data could not sufficiently support this hypothesis. Therefore, additional research on different aspects of caste regulation is required to fully understand its mechanism in pharaoh ants.