Cannibalism of diploid drone larvae in the honey bee (Apis mellifera) is released by odd pattern of cuticular substances
Giulia Santomauro, Neil J Oldham, Wilhelm Boland, Wolf Engels
In order to decipher the assumed scent signals from diploid drone larvae which release the cannibalism behaviour of nursing worker honey bees, cuticular extracts of newly hatched and unfed live larvae were made by brief washes in pentane. The first instars were sexed using a recently improved method. The extracted cuticular substances of diploid drones, diploid workers and haploid drones were analysed by gas chromatography-mass spectrometry. Greater quantities of cuticular compounds were obtained from male than from female larvae, with the diploid drones having a little less than the haploids. The main components in the first instar larval spectrum were identified as four alkanes and squalene, present in the extracts of all three larval types, but in different amounts. No substance was found to occur exclusively on the diploid drones. Our analyses clearly indicate pronounced quantitative but no qualitative peculiarities in the pattern of cuticular secretions on first instar diploid drone larvae. The pattern differs from both the worker and the normal drone composition and is presumably perceived as odd by the nursing worker bees. This assumption was bioassayed with dummies impregnated with blends copying the quantitative pattern of the five main components as determined for the three types of larvae. The brood cells containing diploid drone ‘dummies’ (shaped from paraffin) were emptied significantly faster than those with the worker and haploid drone odour or the controls. According to these within-colony test results, the adult bees can recognize diploid drones by their particular pattern of cuticular secretions. Neither the previous notion of a cannibalism substance nor that of a diminished production of pheromones could be confirmed. Implications of this infanticide on inclusive fitness of the superorganism bee colony and evolutionary aspects in relation to the hymenopteran sex determination are discussed.
Apis mellifera, diploid drones, larval cannibalism, cuticular substances, larval discrimination bioassay, inclusive fitness, evolution of sex determination