Abstract
Once a hornet is captured within a bee ball, the temperature, CO2 concentration, and humidity in the bee ball are increased rapidly by honeybees’ respiration. Within 5 min after capture, the temperature reaches 46℃ and CO2 concentration 4％, and the relative humidity rises gradually as high as 90％ or above in 3-4 min. Normally, the hornet dies within about 10 min in the bee ball. To investigate conditional changes within the bee ball, i.e., the main causes of hornet mortality, we determined the lethal temperature on the 10-minute exposure of hornets in various conditions of the temperature, humidity, and CO2/O2 concentration. In expiratory air (3.7％ CO2), the lethal temperature was 2℃ or more lower than that of the normal atmosphere. All four hornet species used in the experiment were killed at 44-46℃. Death was not caused by oxygen deficiency because the lethal temperature shows no change even if oxygen is supplied to compensate for the reduced oxygen due to increased CO2. Honeybees adapt to a high CO2 and high humidity environment because they normally cluster. Thus, the lethal temperature of honeybees is 50-51℃ in such an environment, almost the same as that in the normal atmosphere. Japanese honeybees generate heat by intense respiration. They simultaneously produce a high CO2 and high humidity environment to lower the lethal temperature of hornets. European honeybees are usually victims of genocide without our protection in the habitat of hornets, but Japanese honeybees kill the predator without sacrificing themselves using heat and all by-products of respiration.
