Differences in Heat Sensitivity between Japanese Honeybees and Hornets Under High Carbon Dioxide and Humidity Conditions Inside Bee Balls

Abstract

Upon capture in a bee ball (i.e., a dense cluster of Japanese honeybees forms in response to a predatory attack), an Asian giant hornet causes a rapid increase in temperature, carbon dioxide (CO₂), and humidity. Within five min after capture, the temperature reaches 46°C, and the CO₂ concentration reaches 4%. Relative humidity gradually rises to 90% or above in 3 to 4 min. The hornet dies within 10 min of its capture in the bee ball. To investigate the effect of temperature, CO₂, and humidity on hornet mortality, we determined the lethal temperature of hornets exposed for 10 min to different humidity and CO₂/O₂ (oxygen) levels. In expiratory air (3.7% CO₂), the lethal temperature was ≥ 2° lower than that in normal air. The four hornet species used in this experiment died at 44-46°C under these conditions. Hornet death at low temperatures results from an increase in CO₂ level in bee balls. Japanese honeybees generate heat by intense respiration, as an overwintering strategy, which produces a high CO₂ and humidity environment and maintains a tighter bee ball. European honeybees are usually killed in the habitat of hornets. In contrast, Japanese honeybees kill hornets without sacrificing themselves by using heat and respiration by-products and forming tight bee balls.

European honeybee defense against Japanese yellow hornet using heat generation by bee‐balling behavior

“…Although the bees near the bee‐ball center must suffer high temperatures and are surrounded by other hot bees, no honeybees died during bee‐balling. The LD 50 for honeybees in normal air is reported to be 50.8°C (Sugahara et al ). From our results, the average temperature in the bee‐ball was 44.0°C, so honeybees have sufficient margin to survive the temperature in the bee‐ball.…”

“…A bee‐ball of A. cerana may have other factors that kill hornets, including heat, CO 2 and high relative humidity (Ono et al ; Sugahara et al ). In our work, the same temperature as inside the A. mellifera bee‐ball with low humidity killed hornets in bee‐less bottle experiments (Fig.…”

Carbon dioxide sensitivity and its role in multifunctional neurons in the mollusk Onchidium

“…Additionally, the gating mechanisms of excitation brought about by CO 2 remain unclear (Luo et al, 2009). In contrast to these molecular biological experiments, CO 2 gas detection has been demonstrated behaviorally in the honeybee (Sugahara et al, 2012). These data indicate that direct detection of CO 2 is a common property of the nervous systems of both vertebrates and invertebrates.…”

Identification of kakusei, a Nuclear Non-Coding RNA, as an Immediate Early Gene from the Honeybee, and Its Application for Neuroethological Study

“…The high temperature phase continues for approximately 20 min. Within approximately 30 to 60 min after initiating the bee ball formation, the hornet is killed by the heat [48,50] (Figure 5A–D). This anti-predator behavior is a good example that selective pressure to avoid predation resulted in species-specific behavioral evolution [47].…”

“…Because Acks is preferentially expressed in the class II KCs of the fighting workers and heat-exposed workers, we also speculate that class II KCs functions for thermal sensing to appropriately regulate heat generation during forming the bee ball. The Japanese honeybee workers fight against the giant hornet by utilizing the small (3–5 °C) difference in lethal temperature between them (the lethal temperature of the giant hornet is approximately 45 °C, while that of the Japanese honeybee workers is 49 °C) [48,50]. Therefore, precise temperature monitoring and control of heat production is vital to Japanese honeybee workers.…”