Establishment of an Olfactory Conditioning Assay for Two Solitary, Cavity-Nesting Bees

To better understand insect learning ability, demonstration of learning through conditioning is an effective research tool. Conditioning in social bees takes advantage of the proboscis extension reflex (PER) as a response to an unconditioned stimulus (US) (e.g., sucrose solution). The US is then associated with a conditioned stimulus (CS) (e.g., an odor) to elicit PER. However, solitary bees do not readily exhibit a PER when restrained and then prodded with an offering of sucrose. Managed solitary bees can be maintained in laboratory benchtop cages where they discover and feed from wicks soaked with aqueous sugar or honey. We sought to devise a protocol that demonstrates learning through simple conditioning for two managed solitary bees, Osmia lignaria and Megachile rotundata by exploiting their ability to locate a small feeder and reflexively extend the proboscis to retrieve a sucrose reward (US). In this study, the rewarded feeder was paired with a floral odor (CS) during training bouts. Newly emerged adult bees began training on the day of their emergence, continued training for another day, and were tested on the next day using a choice bioassay that revealed whether bees had learned the CS. The conditioning assay was effective for both bee species and sexes as revealed by proboscis extension towards material dosed with the reward-associated training odor. The ability to condition solitary bees could support important studies that address questions related to bee preferences for nesting and floral resources and for effects of pesticides or other stressors on learning and memory.