Abstract
Extracts of queens or synthetic 9-oxo-trans-2-decenoic acid (9-ODA) partially inhibited queen replacement in colonies following the removal of the queen. Synthetic 9-hydroxy-trans-2-decenoic acid (9-HDA) was ineffective and not synergistic with 9-ODA. During the swarming season, a continuous treatment with 9-ODA did not decrease the number of queen cups and queen cells built by queenright colonies.