Functional resin use in solitary bees

1. Overall, more than 30% of bee species depend on non-floral resources, such as resin. However, the importance of resin in bee ecology, particularly for solitary bees, has received very little attention thus far. 2. A plethora of loose natural history observations, inferences, and author opinions hint towards a striking range of uses of resin for nesting by bees. In this review, we focus on resin use in solitary bees and identify extant knowledge, knowledge gaps, and future research directions with regard to the functional use of resin in bee nesting biology. 3. Resin use in solitary bee nests can be broadly grouped by functional roles for nest structure, chemical camouflage, defence, moisture regulation, and anti-microbial properties. We point out that resin usage appears to be constrained by environmental and physiological factors. Bee species-specific tolerances for resin toxicity and resin availability in the environment seem to determine resin choices and subsequently functional usage in nests. We finally highlight that resin may play a major role in determining the ambient nest microbiota, due to its strong antimicrobial properties. We conclude that a better mechanistic understanding of resin use in bee nesting biology can aid in assessing species range shifts in light of global change.