Optimal Cold Temperature for the Artificial Hibernation of Bombus ignitus Queen Bumblebees

Abstract

Bumblebees are widely used to pollinate various greenhouse crops. Among the different bumblebee species, Bombus ignitus is indigenous to Korea, China, Japan and Russia. B. ig-nitus undergoes one generation per year, and artificial hibernation is essential for year-round rearing of the bumblebee. Keeping the queens under low-temperature conditions for several months is an effective method for terminating their diapause and promoting colony development. In the present study, we investigated how cold temperature affects the artificial hiberna-tion of B. ignitus queens. Under chilling temperatures of-2.5°C, 0°C, 2.5°C and 5°C with constant humidity >80%, the queens stored at 2.5°C exhibited the highest survival rates, which were 74.0% at one month, 67.0% at two months, 60.0% at three months, 46.0% at 4 months, 33.0% at 5 months and 24.0% at 6 months. Lower survival rates were observed at 0°C, 5°C, 7.5°C and 12.5°C. At 2.5°C the colony developmental characteristics after diapause were 1.2-to 1.5-fold greater than those when queens were stored at 5°C. Thus, 2.5°C and 70% R.H. were the most favorable chilling temperature and humidity conditions for terminating the dia-pause of B. ignitus queens.