Temperature as a causative factor in the seasonal colour dimorphism of Apis cerana japonica workers

Abstract

The pigmentation of the scutellum, sclerites of the 3rd and 4th tergites, and the abdominal ventral side of Japanese honey bee workers was examined. A predominantly yellow (summer) type of worker appeared from August to October, whereas a black (winter) type appeared from late October to May. The pigmentation grades differed among colonies collected from different regions of Japan. When pupae were kept at 25-!8°C in the laboratory, the resultant adult pigmentation was affected. The yellow type appeared at temperatures higher than 34°C, and the black type appeared at temperatures lower than 30°C. The temperature at several places in a colony was measured using microthermistors. At the central brood area, it was consistently 33—34°C and the peripheral area fluctuated from 30° to 34°C. The seasonal colour variation in the Japanese honey bee in relation to the accuracy of thermoregulation in the brood area is discussed.