Colony vs hornet: The ball effect
Bees have various defensive strategies when confronted with threats, showcasing extraordinary behaviour that is subject to multiple studies. Honeybees utilize propolis, stinging, pheromone attacks, and ball formations as tactics against predators.
The never-ending battle between honeybees and hornets shows a continuous coevolution between the two species. Hornets, being social insects, prey on honeybees, seizing newborns to nourish their larvae with a protein-rich diet. However, Cyprian honeybees have devised an ingenious method to counter this threat.
When Cyprian honeybees form a thermal ball, the core temperature reaches an average of 44°C, which is below the lethal threshold for hornets. A hornet that is trapped in these thermal balls for a short period of time (5-8 minutes) initially become immobile for a few minutes before regaining mobility. Thermal balls alone are insufficient to eliminate an Oriental hornet, which possess a high tolerance to elevated temperatures.
So, how do Cyprian honeybees manage to overcome this challenge?
They have adapted by developing a mechanism known as asphyxia-balling specifically targeted at dealing with an Oriental hornet, distinct from the thermo-balling observed in Japanese honeybees where the core temperature alone is enough to kill the murderer hornet.
In the asphyxia-balling strategy, Cyprian honeybees form a ball around the hornet, focusing on a particular segment of its abdomen crucial for respiratory function. By maintaining pressure on this segment, the bees induce hypoxia and subsequently hypercapnia in the hornet. Hypoxia occurs when tissues lack sufficient oxygen to maintain homeostasis, while hypercapnia results from increased carbon dioxide levels due to water loss. This combination of factors, combined with the elevated ambient temperature within the ball, proves fatal to the hornet.
While temperature alone is insufficient to dispatch the Oriental hornet, it significantly contributes to its demise when coupled with respiratory system dysfunction. However, finding the Achilles heel of a hornet is not enough. This method of defence comes at a cost, it is energy-intensive for the bees. Moreover, relying solely on asphyxia-balling is not sustainable for combating entire hornet colonies and could ultimately weaken honeybee populations.
Hence, human intervention remains vital for protecting these essential pollinators from their greatest predator, the hornet.
To combat hornets, several strategies can be employed. Firstly, installing physical barriers or screens in vulnerable areas can effectively prevent hornet access. Seeking professional assistance is another crucial step, as trained experts can safely remove hornet colonies. Additionally, using traps baited with attractants can help reduce the hornet population. Finally, chemical control can be implemented to further manage hornet numbers and mitigate their impact.
by Rana Slim, Agricultural Engineering student at the Saint Joseph University