Rodent odour bait: A new bumble bee conservation tool to enhance nest box occupancy

Abstract Bumble bee conservation focuses on supplementing floral resources. Yet, nesting site availability is linked to bumble bee abundance. As a supplement to natural nest sites, nest boxes could be deployed and baited with synthetic lures. As queen bumble bees reportedly establish colonies in abandoned rodent burrows, we hypothesized (1) that queen bumble bees sense, and behaviourally respond to, rodent odour, and (2) that lures of synthetic rodent odour can guide spring queens to nest boxes. We collected headspace odorants from bedding soiled with urine and faeces of house mice, Mus musculus , and identified the 10 odorants that elicited responses from queen antennae. To field‐test attraction of queens to mouse excreta odorants, we tree‐mounted paired nest boxes in florally rich locations, and assigned clean and soiled bedding, respectively, to one box in each pair. Queens established colonies in 17 mouse‐scented boxes and in six unscented boxes. This 43% occupancy rate of mouse‐scented boxes represents a significant improvement over the 10% occupancy rate common for unscented boxes. In a further field experiment, we baited one box in each pair with a synthetic mouse odour lure and found that queens established colonies in 13 baited boxes and in six unbaited control boxes. Specifically, Bombus mixtus established seven colonies in baited boxes and only one colony in an unbaited box. With this proof‐of‐concept that synthetic lures can guide queens to nest boxes, we anticipate that bumble bee conservation programs will soon be able to offer both expanded floral resources and baited nest boxes readily detectable by queens.