Defence reactions of Apis mellifera ligustica against attacks from the European hornet Vespa crabro

Abstract

The predatory behaviour of Vespa crabro hornets on the honeybee Apis mellifera ligustica and the counter strategy of the prey were observed and described in two apiaries of 27 and 41 colonies in Central Italy. Observations were carried out in the second half of October and accompanied by experiments aimed at determining the mechanisms of honeybee defence. We confirmed that V. crabro represents a relatively mild predator for A. mellifera ligustica but it can have a considerable impact on already debilitated colonies. Hornet predatory strategy is to spot then swoop on returning foragers. Honeybee defence centres on forming packed aggregations of individuals near the hive opening, which probably deters the wasps from entering. Coordinated behaviour by the bees, which cling together in groups, can knock the approaching hornets down, which are then totally covered by the bees. This balling behaviour has the effect of over-heating the predator whose lethal thermal limit is about 44 °C, although other factors, such as carbon dioxide emission and the release of venom by the honeybees, may also contribute to the death of the hornet. Comparing the differences and similarities of this behaviour with those observed in other species of Apis and Vespa reveals that these two species are an interesting model for the study of the evolutionary arms race.