Honey bee social collapse arising from hornet attacks

Abstract

Collective defense is constrained by co-evolution with the predator such that species typically have effective defenses against sympatric, but not allopatric, predators. The honey bee, Apis mellifera, is allopatric with the predatory hornet, Vespa velutina auraria, and does not have effective defenses, unlike A. cerana, which is sympatric with this hornet. However, the reasons behind the decline of attacked A. mellifera colonies remain to be fully elucidated and are relevant given that invading V. velutina contributes to the decline of A. mellifera in multiple European countries. In southwest China, we show that A. mellifera ligustica, unlike the native A. cerana cerana, severely reduced foraging, and experienced higher hornet predation of foragers when attacked by native V. velutina auraria. Attacks resulted in reduced queen egg production, fewer pupae, and fewer workers and led to A. mellifera colony death. Decline began after only one week of hornet attacks, with A. mellifera queens significantly reducing their egg-laying even though the number of colony workers had not significantly fallen. In contrast, hornet attacks did not lead to declines in the same proxy measures of colony fitness for A. cerana. We suggest that, in addition to direct predation, predator-induced stress may contribute to A. mellifera colony declines, an intriguing possibility that accords with a growing body of research demonstrating that such stress can directly harm reproduction and thereby reduce fitness in multiple animals.