Hormonal modulation of brood allocation underlying evolutionary conflicts in the supercolonial ant Tapinoma darioi

In social insects, caste fate is typically determined by larval feeding, but in several species juvenile hormone (JH) also regulates caste development, with elevated JH levels biasing brood towards queens. In some ants, maternal endocrine signalling could influence brood developmental trajectories, potentially biasing caste-fate. We hypothesized that in polygynous societies, individual queens could gain fitness advantages over co-nesting reproductives by increasing JH deposition, thereby producing more sexuals that are reared by workers with low relatedness. To test this, we conducted a bioassay in the supercolonial ant Tapinoma darioi, experimentally altering JH signalling in queens using methoprene (a JH analogue) and precocene II (a JH synthesis inhibitor), while monitoring brood production. Our results show that workers detect and cull excess larvae at a defined developmental window, revealing for the first time the precise moment at which this occurs. These findings are consistent with the hypothesis that maternal endocrine signalling can bias brood outcomes, particularly in supercolonial species where sexual larvae are often reared by unrelated workers. At the same time, our data indicate that workers are not at a loss in this evolutionary conflict of interests, since they can detect and cannibalize excess larvae, likely adjusting the queen/worker ratio towards the colony’s optimum from their own evolutionary perspective. Overall, our study highlights the dynamic interplay between maternal control and worker counter-adaptation in shaping caste determination, providing new insights into the mechanisms and evolutionary conflicts underlying social insect reproduction. Our research highlights the intense reproductive competition that occurs in insect societies comprising large numbers of coexisting queens. We show that experimental manipulation of juvenile hormone signalling in queens is associated with changes in worker-mediated larval removal in the supercolonial ant Tapinoma darioi. These findings are consistent with a role of maternal endocrine state in shaping brood allocation dynamics under conditions of reproductive conflict. We also describe how workers can counterbalance such dynamics through larval cannibalization, likely contributing to the regulation of queen-to-worker ratios and the maintenance of colony stability. Overall, our study provides new insight into how endocrine processes and worker behaviour interact in the evolutionary conflicts that structure social insect societies.