Choosing collection methods and sample sizes for monitoring bees

Abstract

Abstract Establishing protocols to sample and monitor bees is critical as pollinators decline. Bees are collected using passive and active methods, but choosing which method and how many samples to collect is challenging. We collected bees in pan traps, vane traps and target netting (bumble bees only) at 96 locations across Wyoming from the sagebrush steppe to mountain meadows. We used power analysis to estimate the number of samples needed to detect a change in bee and bumble bee abundance and richness across elevations (1120–3308 m). Vane traps and pan traps required a similar number of samples to detect a change in the abundance and richness of bees; however, vane traps caught four times more bees and 97% of genera compared to pan traps. Vane traps required far fewer samples to detect changes in the abundance and richness of bumble bees compared to target netting. Pan traps caught so few bumble bees that we do not recommend using them. We recommend using seven to nine vane traps to monitor the abundance and richness of bees and bumble bees, and supplementing bumble bee monitoring with target netting when possible.