Lethality of Honey Bee Stings to Heavily Armored Hornets

SIMPLE SUMMARY: The co-evolution of attack and defense strategies between Apis and Vespa is a good model for studying arms races. Some honey bee species and subspecies can kill hornets with heat balls that generate heat and carbon dioxide. However, the role of stinging as a defense against hornets has been discounted, even though stings and venom are important honey bee weapons. No studies, to date, have tested the role of bee sting venom alone or in conjunction with elevated temperature on hornet survival. We found that bees can sting hornets but most hornets (87%) are able to remove bee stings less than 1 min after being stung, perhaps explaining why stinging is not considered a major anti-hornet defense. However, we show that such bee stings can kill hornets and demon-strate that the combination of sting venom and being heated is the most lethal to hornets. ABSTRACT: 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.