Methoprene, a Juvenile Hormone Analog, Causes Winter Diapause Elimination in Univoltine Bee Species Osmia bicornis L.

SIMPLE SUMMARY: Diapause is physiological state of developmental arrest and dormancy, which is genetically determined and mediated by neurohormones. Diapause process is an opportunity for insects to survive seasonal environmental changes. Red mason bee Osmia bicornis is an univoltine species with imaginal diapause, and it is used for crop pollination. Our work shows that obligatory diapause in O. bicornis can be modified by a juvenile hormone analog. Treating pupae or young imagoes in cocoons during the pre-wintering period with a JHA (methoprene) can prevent winter diapause and induce the emergence of adult bees in October when development was accelerated in the laboratory or in November when bees developed outdoors according to their life cycle. More sensitive to methoprene is the imago than the pupa, but earlier application of JH analog can accelerate the emergence of adult bees. Our study suggests that JH levels during the pupal stage and soon after adult eclosion are related to hormonal regulation of winter diapause in O. bicornis. On the other hand, a better understanding of the mechanisms of reproductive diapause can help us improve the management of Osmia bees as commercial pollinators that can be used regardless of the emergence period in nature. ABSTRACT: Osmia bicornis syn. O. rufa is a univoltine bee species in which adults fly in spring and the offspring overwinter as cocooned imagoes. The flight period of solitary bees is short, so methods of control for development and emergence time are needed to synchronize the activity of managed pollinators with blooming. In our study, we tested the effectiveness of a juvenile hormone analog for the prevention of winter diapause. Bees developed in settled nests outdoors or in the laboratory (22 °C) until the end of the pre-pupa stage, then cocoons were removed from the nest cells and treated with a JH analog—methoprene—during the pupa and young imago stages. Then, bees were activated at 25 °C until the adults left the cocoons. Topical application of methoprene to the cocoon at the pupa or imago stage induced the emergence of some adult bees in the pre-diapause period, while no adults emerged when the bees were not treated with methoprene. Most adults emerged (about 50%) when treated with methoprene on 3-week-old cocooned imagoes. Bees treated in the pupal stage had a lower emergence rate (20–30%), but adult bees emerged earlier. The emergence time of adults for the laboratory group was, on average, from 70 to 91 days, and that for outdoor groups was from 57 to 72 days.