Cold storage alters the fat-trehalose trade-off, decreases the flight ability, and maintains the high survival rate and flight speed of Osmia excavata (Hymenoptera: Megachilidae).

Abstract

Osmia solitary bees are important pollinators of various crops worldwide. Refrigeration has been widely used to synchronize the emergence time of Osmia species from cocoons with the blooming time of different crops, but the fitness of Osmia after refrigeration remains unknown. Here, the effects of long-term refrigeration at 0°C on the vitality, flight ability, and metabolism of Osmia excavata, which is known as the "king of pollination" in China, were studied. The survival rate (>90% before 120d), weight loss rate (<15% after 170d), and mean flight speed of O.excavata were not greatly affected after long-term refrigeration. The content of fats, which have antifreeze and energy storage properties, was not significantly altered in O.excavata before 130d of refrigeration, which might explain why the survival rates and flight speed of O.excavata remained high after long-term refrigeration. However, the flight duration and distance decreased significantly (P<0.05), and both were positively correlated with the reduced trehalose levels in O.excavata (r=[+0.69]-[+0.71]; P<0.05). Overall, these findings indicate that the pollination potential of O.excavata for various crops with different flowering periods is high after long-term refrigeration; however, long-term refrigeration may decrease pollination efficiency. Our findings highlight new research directions that could improve the ecological service function of refrigerated O.excavata.