Evaluation of Osmia excavata (Hymenoptera: Megachilidae) sensitivity to high-temperature stress

Abstract

The population of Osmia excavata, an important pollinator in commercial orchards, has been in serious decline over recent years. To evaluate the risk of high-temperature stress on O. excavata, we evaluated the high-temperature tolerance and potential physiological and biochemical responses of O. excavata after a series of high-temperature stresses. The results showed that the mortality rates of O. excavata increased gradually with increases in temperature and duration of stress (R2 = 0.88–0.99; p < 0.05). The larvae of O. excavata were more sensitive to temperature stress than adults, and the median lethal time (LT50) value of the former was smaller than the latter in the acute response test. By comparing the results of acute and chronic responses of O. excavata to high-temperature stress, we found that the LT50 values of natural cocoon-break adults at slightly higher temperatures (35°C and 40°C) were smaller than those of artificial cocoon-break adults, but the LT50 values were similar under extreme high-temperature stress (45°C). Furthermore, the acute and chronic responses on the fat content of adult Osmia obtained by artificial and natural cocoon-break methods were significantly different (F = 5.03; p < 0.05). Additionally, the mortalities of the young larvae and artificial cocoon-break adults were both significantly and positively correlated with trehalose content (r = 0.78–0.82, p < 0.05). However, the mortality of the natural cocoon-break adults was negatively related to the acetylcholinesterase activity (r = −0.93, p < 0.001). Overall, these results suggested that O. excavata has a low tolerance to high-temperature stress and provide evidence of causes that could be contributing to the population decline of O. excavata.