The heat ball defense of honey bees against their sympatric hornet predators is a classic and spectacular outcome of a co-evolutionary race. Hundreds of bees can encapsulate a hornet within a large ball that kills it with elevated heat. However, the role of stinging in this defense has been discounted, even though sting venom is an important weapon in bees. Surprisingly, no studies have tested the role of bee sting venom alone or in conjunction with elevated temperature on hornet survival. We surveyed dead Vespa velutina hornets found near and inside Apis cerana colonies and found stings retained in hornet bodies, most often in an intersegmental neck-like region, the veracervix. Experimentally stinging hornets in this region with A. cerana and Apis mellifera guards significantly increased hornet mortality. The combination of sting venom and elevated heat ball temperature (44 °C) was the most lethal, although there was no synergistic interaction between sting venom and temperature. As expected, hornet mortality increased when they were stung more often. The average amount of venom per insect species and the length of stinger lancets correlated with insect mass. Sting venom thus remains important in the arms race between bees and their hornet predators.

Animal-pollinated plants face a common problem, how their defensive anti-herbivore compounds may impair or alter pollinator behavior. Evolution has tailored multiple solutions, which largely involve pollinator tolerance or manipulation, to the benefit of the plant, not the removal of these compounds from pollen or nectar. The tea plant, Camilla sinensis, is famous for the caffeine and tea polyphenols (TP) that it produces in its leaves. However, these compounds are also found in its nectar, which honey bees readily collect. We examined the effects of these compounds on bee foraging choices, learning, memory, and olfactory sensitivity. Foragers preferred a sucrose feeder with 100 µg or 10 µg TP/ml over a control feeder. Caffeine, but not TP, weakly increased honey bee learning. Both caffeine and TP significantly increased memory retention, even when tested 7 d after the last learning trial. In addition, TP generally elevated EAG responsiveness to alarm pheromone odors. These results demonstrate that other secondary plant compounds, not only caffeine, can attract pollinators and influence their learning and memory.

The stop signal is produced in response to negative experiences at the food source and inhibits honey bee (Apis mellifera) waggle dancing. Here, we present a protocol for measuring the effects of an inhibitory signal associated with danger on honey bee dopamine levels. We describe steps for observing honey bee colonies, training them with artificial nectar, and simulating hornet attacks. We then detail procedures for recording waggle dancing and stop signals and measuring brain dopamine levels during different treatments. For complete details on the use and execution of this protocol, please refer to Dong et al.1.

Positive and negative experiences can alter animal brain dopamine levels.¹ When first arriving at a rewarding food source or beginning to waggle dance and recruit nestmates to food, honeybees have increased brain dopamine levels, indicating a desire for food.² We provide the first evidence that an inhibitory signal, the stop signal, which counters waggle dancing and is triggered by negative events at the food source, can decrease head dopamine levels and dancing, independent of the dancer having any negative experiences. The hedonic value of food can therefore be depressed simply by the receipt of an inhibitory signal. Increasing the brain dopamine levels reduced the aversive effects of an attack, increasing the time that bees spent subsequently feeding and waggle dancing and decreasing their stop signaling and time spent in the hive. Because honeybees regulate food recruitment and its inhibition at the colony level, these results highlight the complex integration of colony information with a basic and highly conserved neural mechanism in mammals and insects.² VIDEO ABSTRACT.