EVIDENCE OF PHEROMONAL QUEEN CONTROL OVER THE PRODUCTION OF MALE AND FEMALE SEXUALS IN THE FIRE ANT, SOLENOPSIS-INVICTA
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Two hypotheses that could explain social regulation of the production of sexuals in Solenopsis invicta were investigated: (1) differences in worker/larva ratios; and (2) pheromonal regulation by queens. Small laboratory units (fragments of multiple-queen, i.e. polygyne, colonies) were found to be capable of producing sexuals and to be sensitive in this regard to differences in queen number; the presence of even a single queen inhibited the numbers of sexuals (male and female) produced in comparison with queenless controls. To determine whether differences in worker/larva ratios were involved in this inhibition, a greater number of eggs than could be laid by a single queen was added daily to queenless units. These units produced more sexuals than similar units containing one queen, but did not differ from queenless controls which did not receive eggs. These results rule out the possibility that differences in worker/ larva ratios significantly affected the production of sexuals in such experimental units. They also exclude the possibility that chemical cues were transmitted by queens via their eggs. To test the hypothesis that queen pheromones were involved, freshly killed corpses of functional (egg-laying) queens were added daily to queenless units. These effectively inhibited the production of sexuals, although not as effectively as living queens. On the other hand, corpses of alate virgin (non-egg-laying) queens did not inhibit the production of sexuals. The addition of live queens to previously queenless units in which large sexual larvae had developed resulted in the execution of most of these larvae by workers, indicating that queen control over the production of sexuals can act retroactively after larvae are sexualized. A similar but less pronounced result was obtained by the addition of functional queen corpses. These results provide evidence that functional queens exert control over the production of sexuals in S. invicta through pheromones that influence the behavior of workers toward both male and female larvae. 1986 Springer-Verlag.