Experimental validation of a rearing protocol for laboratory assays utilizing <i>Osmia lignaria</i> Say (Hymenoptera: Megachilidae)

The blue orchard bee (Osmia lignaria Say) is a solitary bee native to North America that is increasingly propagated, sold, and used for pollination of rosaceous orchard crops. While methods exist to rear blue orchard bees in a laboratory setting, present protocols vary in diet manipulation and fail to progress bees to adult emergence. Variability in published methods also makes standardized comparisons within or across species challenging. Here, we present a validation of a rearing protocol for O. lignaria in a laboratory setting, with the study employed over a 2-year period that mirrored the bees' phenology in northern Utah (United States). Our protocol used 3D printed well plates with a well diameter that we recommend as appropriate for rearing O. lignaria in a laboratory. Each well permits the user to observe detailed life stages of individual O. lignaria bees without disturbing their development. To validate the protocol, we monitored O. lignaria development across 3 larval instars (first, second, and fifth), prepupal, pupal, and adult stages using a dissection scope and X-ray imaging. We confirm that diapause duration can be altered and affects the percent weight loss. Our data demonstrate that we can successfully rear bees to the adult stage (74%). Our protocol can be altered to fit any laboratory experiment and adapted to investigate other above-ground cavity-nesting bee species in a laboratory setting. Such investigations might include how multiple environmental conditions, nutritional factors, and stressors influence bee health.