(Kingwell et al. 2026, Proceedings of the Royal Society B 293: 20260506: https://doi.org/10.1098/rspb.2026.0506 )
Eusociality, a major transition in behavioral evolution, features reproductive division of labor between a primary reproductive individual (queen) and daughters that forego their own reproductive effort (workers). This inherent mother-daughter conflict is often mediated through Queen Pheromones (QPs) – compound blends that trigger helping behavior by workers and delay or abolish their own reproductive maturation. Therefore, QP evolution and its contributions to eusociality are key to understanding insect social evolution, but many lineages (e.g. honeybees, termites) are obligately eusocial and highly derived, with no closely related solitary taxa. The facultatively eusocial sweat bee, Megalopta genalis, provides a model for conditionality in the function of QPs as honest signals of queen fecundity and worker inclusive fitness. Worker M. genalis bees must decide either to remain with their mother and provide care to additional sisters (indirect fitness) or to mate and promote their own reproductive efforts (direct fitness).
Callum Kingwell (above), a recent NBB graduate, led an international team in a study of QP function in M. genalis bees at the Smithsonian Tropical Research Institute (STRI) in Barro Colorado Island, Panama. Callum extracted queen bees and identified several chemical compounds as QP candidates, but only methyl alkanes (MAs) were correlated with queen fecundity, with potential to serve as honest QPs allowing daughters to assess the (indirect) fitness benefits of remaining with their mothers. Next, Callum tested whether MAs function as QPs by reducing mother-daughter reproductive conflict. Remarkably, MAs function both as “releasers”, triggering submissive behaviors upon encounter by workers, and as “primers”, (reversibly) inhibiting ovarian development in workers. Isotope feeder experiments showed that methyl groups in MAs are incorporated from methyl-branched amino acids such a VAL, providing a trans-generational link to amino acid richness in the pollen diet consumed by the queen as a larva. These findings were published on July 29, 2026, in the Proceedings of the Royal Society B: Biological Sciences.
Figure summarizing organizational effects of queen pheromone compounds for Megalopta genalis bees. A: only methyl alkanes (MA) significantly increase worker submissive behavior (abdominal C-posture) upon encounter with plastic bead as a surrogate queen, serving as an immediate “releaser” effect. B,C: MA applied to worker abdomens significantly reduces the workers’ own oocyte development as a “primer” effect.
