Collective defense is constrained by co-evolution with the predator. In social insects, such as honey bees, collective defense of the nest is essential. However, the potential cascading effects of predator attack upon social insects – directly reducing the number of colony members and, indirectly, stressing the colony to reduce its reproduction – are not well understood.

Asian honey bees (Apis species) have co-evolved with predatory Asian hornets (Vespa species) and have evolved multiple counter-strategies. A. mellifera colonies can respond to attacks by V. velutina hornets by creating a dense “bee carpet” consisting of a large number of bees gathered at the nest entrance. However, this defense is not always effective.    

In a study published in Entomologia Generalis, researchers from Xishuangbanna Tropical Botanical Garden (XTBG) and the University of California San Diego predicted that hornet presence would harm A. mellifera more than A. cerana colonies because of their different exposure to V. velutina over evolutionary time.

The researchers measured hornet attacks and honey bee colony proxies of fitness (number of eggs, pupae, and workers) in apiaries with both bee species but with and without hornets and quantified fitness effects over seasons in the presence and absence of hornets.
They found that hornet attacks significantly reduced A. mellifera, but not A. cerana colony fitness. A.mellifera, unlike the native A. cerana, severely reduced foraging, and experienced higher hornet predation of foragers when attacked by native V. velutina auraria.    

They observed that hornet attacks elicited more guarding and stop signaling from A. mellifera than from A. cerana. Attacks resulted in reduced queen egg production, fewer pupae, and fewer workers and led to A. mellifera colony death. In contrast, hornet attacks did not lead to declines in the same proxy measures of colony fitness for A. cerana.   

"In addition to direct predation, predator-induced stress may contribute to A. mellifera colony declines. Our results suggest that a largely ineffective defense such as the A. mellifera bee carpet response can contribute to population collapse in a social group,” said Prof. TAN Ken of XTBG.   

   

Contact   

TAN Ken Ph.D Principal Investigator    

Key Laboratory of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Mengla, Yunnan 666303, China      

E-mail: kentan@xtbg.ac.cn   

   

 Published online: May 3, 2023