Unusual thermal defence by a honeybee against mass attack by hornets

Abstract

THE giant hornet Vespa mandarinia japonica (Hymenoptera: Vespidae) is the only hornet species known to have evolved en masse predation of other social bees and wasps. Here we show that hornets is initiated by secretion of a foraging-site marking pheromone from the van der Vecht glands (metasomal sternum VI glands) by a single foraging hornet. The lone hornet rubs the basal tuft of the terminal gastral sternite around a prey food resource, such as a honeybee colony, and the hornet nestmates then congregate and attack the marked site en masse. The sympatric Japanese honeybee Apis cerana japonica (Hymenoptera: Apidae) can detect the hornet marking pheronome, and responds by increasing the number of defenders at the nest entrance. When an invading hornet is captured by a defending bee, more than 500 other bees quickly engulf the hornet in a ball which contains isoamyl acetate. Thermography showed that the ball temperature is very high (˜47 °C), which proves lethal to the hornet but not to the bees. Defenders patrolling the nest entrance also generate high temperatures. These findings suggest that aspects of the interaction between V. mandarinia japonica and A. cerana japonica are specifically coevolved.