Diapause determination in Osmia cornifrons based on oxygen consumption

Osmia cornifrons mason bees are important pollinators of fruit trees. Diapause treatment is essential for their year-round breeding. We measured oxygen consumption and awakening in O. cornifrons to identify a biomarker for evaluating diapause termination. In O. cornifrons, oxygen consumption increased with the duration of the chilling period and was 1.4–1.8-fold higher in male cocoons than that in female cocoons. Oxygen consumption in O. cornifrons cocoons did not differ significantly among chilling temperatures (0 °C, 2.5 °C, 5 °C, 7.5 °C, and 10 °C); however, regression analysis of oxygen uptake values between 0–5 °C and 7.5–10 °C in male and female cocoons revealed a significant second-order relationship. Oxygen uptake was higher at 7.5–10 °C than that at 0–5 °C during the same chilling periods. Cocoons kept at 7.5–10 °C also exhibited earlier emergence than those kept at 0–5 °C. The average respiration rate of newly awakened adults was 1,400.4 and 4,011.2 µL/mg body weight/h in females and males, respectively, representing a 2.9-fold higher rate in males. Respiratory rate increased with the number of days after emergence. Accordingly, we developed a method using a biorespirometer to quantitatively assess the degree of dormancy and awakening, which has implications for the essential dormancy treatment for year-round breeding of mason bees.