Counting Bees: A Comparison of Survey Methods for Estimating Wild Bee Abundance.

Wild bees are essential pollinators in many natural and agricultural systems. However, wild bees and other pollinators are currently experiencing an unprecedented population decline. Researchers commonly rely on passive sampling methods such as pan traps to monitor pollinator populations, but the effectiveness of these methods has never been directly validated by absolute population estimates. To test the efficacy of pan traps, we conducted a mark-recapture study and deployed pan traps at three sites in the Butner-Falls of Neuse Game Lands near Raleigh, NC, in summer of 2020. We hypothesized that pan trap capture rates would not provide a valid proxy for bee population size. To estimate absolute population sizes of bees at three sites, we conducted mark-recapture surveys for four taxa: carpenter bees (Xylocopa virginica), green sweat bees (Augochlorella sp., Augochlora pura, and Augochloropsis sp.), longhorn bees (Melissodes bimaculatus), and leafcutter bees (Megachile sp.). We repeated the surveys for five total weeks, then compared the resulting population estimates to pan trap and aerial netting data collected at the same sites in alternate weeks by the NC Wildlife Resources Commission. Our results support our prediction that pan traps are highly biased and do not reflect absolute population sizes of the bees in this study. This study is the first to attempt a direct comparison of common pollinator monitoring techniques with absolute population estimates generated from mark-recapture surveys at the community level. The results of this study indicate that more research is required to validate common monitoring protocols for these critically important but threatened pollinator species. [ABSTRACT FROM AUTHOR]