Influence of pyriproxyfen, a juvenile hormone analogue, on diapause termination in the solitary bee, Osmia lignaria

In the blue orchard bee (Osmia lignaria), reproductive diapause is an obligatory physiological state enabling winter survival. Under agricultural management, diapause termination potentially provides a tool for synchronizing adult emergence with the flowering period. This study evaluated the post-treatment effects of exogenous application of the juvenile hormone analog, pyriproxyfen, on diapause termination, adult longevity and oxidative stress. The freshly capped O. lignaria nests containing developing larvae were kept in an incubator at 25°C and 75% relative humidity. As they entered diapause, four different treatment groups were established: early emergence control, acetone (vehicle) control, pyriproxyfen treatment, and a control in which bees emerged after diapause. Our results revealed that the topical application of pyriproxyfen (5µg/bee) successfully terminated diapause. Cumulative emergence reached 100% after seven days for males and six days for females. Kaplan-Meier survival analysis demonstrated a significant difference (log-rank p< 0.001) in the emergence timing among treatments for both males and females. Post-treatment longevity was also significantly influenced by treatment (p< 0.005), where pyriproxyfen-treated bees lived longer than bees that emerged after diapause, suggesting an upstream physiological relevance of early diapause termination. Oxidative stress was evaluated for three treatment groups: early emergence control, acetone (vehicle) control and pyriproxyfen through the total antioxidant capacity (TEAC assay) and lipid peroxidation (MDA assays). Our results showed that there is no treatment difference, suggesting that pyriproxyfen-induced changes in survival and emergence do not disrupt oxidative homeostasis. These findings demonstrate the potential efficacy of pyriproxyfen for diapause termination.