Photoperiod during nest construction influences diapause status in the alfalfa leafcutting bee (Hymenoptera: Megachilidae)

Diapause initiation is determined by photoperiod and temperature in many insect species. In the solitary cavity-nesting bee Megachile rotundata, which undergoes facultative diapause as a prepupa, photoperiod is an important cue for diapause induction. However, it is unknown if the mother or offspring makes the decision to induce diapause or when this decision is made. Our goal was to answer these questions by manipulating photoperiod during different stages of development in M. rotundata. We subjected mothers to three different photoperiods as pupae and released them into the field to build nests and lay eggs when those same photoperiods occurred naturally. Offspring were collected and subjected to the same photoperiods as the mothers. We examined the effects of photoperiod on offspring diapause and the number of nests and brood cells created during each photoperiod. Our findings indicate that the photosensitive period occurs in the field, suggesting that the mother determines diapause during nest construction. We also found that reproductive output is the highest during the shortening photoperiods associated with midsummer. This study furthers our understanding of how diapause functions in Megachile rotundata and could be used to advance commercial management practices.