Mason bees do not detect imidacloprid in soil:  A new methodology for assessing Osmia lignaria (Hymenoptera: Megachilidae) soil choice in controlled laboratory environment

Many wild bees use soil as nesting material or as nesting substrate and may thus be vulnerable to direct exposure to imidacloprid in soil.  At the landscape level, concentrations of imidacloprid residue are limited to the immediate areas of treatment, and thus risks to soil-collecting bees could be low if they have a choice of soils and are able to select soils which are not contaminated.  Here we report the development of a new methodology for Osmia lignaria Say to collect soil and seal nest holes in well plates a laboratory setting, and conduct experiments with this methodology to determine if female Osmia are prone to selecting imidacloprid-contaminated soil for nesting material. We combine results of this new methodology with a more traditional experimental setup using choice chambers, to draw some preliminary conclusions about soil choice in female Osmia lignaria. The results from these trials do not reveal a any discernment between treated and untreated soil by adult female bees, for either choice chamber or dormitory nesting experiments, even at high levels of contamination.  These results can help inform risk assessments for soil-interacting wild bees, and the methodologies developed for this experiment can be useful for experimental assessments of female soil and pollen preferences in controlled laboratory settings.