Soldier determination in Pheidole bicarinata: Inhibition by adult soldiers

In the ant Pheidole bicarinata, adult soldiers suppress the induction of soldier developments in larvae that have been treated with methoprene, as well as in acetone-treated controls. Induction of soldier development is inhibited in methoprene-treated larvae when the adult soldiers are present as nurses, when they are present in the colony but minor workers serve as nurses, and when they are held in a minor worker-permeable cage to prevent them from contacting larvae. Suppression of soldier determination can be overridden by high doses of methoprene applied during the juvenile hormone-sensitive period for soldier determination. The degree of suppression increases with increasing contact between larvae and adult soldiers. The most likely mechanism of inhibition is a contact soldier pheromone. On the basis of our results, we expand our model of soldier determination to accommodate the fact that the threshold titre of juvenile hormone necessary to induce soldier development changes in the presence of soldiers. A threshold that is sensitive to the presence of adult soldiers provides a mechanism whereby the worker caste ratio in colonies can be regulated.