SummaryRemoval of the mandibular glands from workers ofApis mellifera capensisdid not interfere with their becoming reproductively dominant in a group ofApis mellifera melliferaworkers. Activation of the ovaries of themelliferaworkers was inhibited in the presence of Cape bees either with or without their mandibular glands. Gas chromatography plus mass spectrometry confirmed that the main component of the mandibular glands was (E)-9-oxo-2-decenoic acid (75% by weight).