Odor discrimination after olfactory conditioning of managed solitary bees, Osmia lignaria and Megachile rotundata

Authors: STANLEY-STAHR, CORY - Utah State University; Pitts Singer, Theresa

Submitted to: Journal of Insect Behavior
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/18/2023
Publication Date: 6/6/2023
Citation: Stanley-Stahr, C.A., Pitts Singer, T. 2023. Odor discrimination after olfactory conditioning of managed solitary bees, Osmia lignaria and Megachile rotundata. Journal of Insect Behavior. 36:180-194. https://doi.org/10.1007/s10905-023-09825-8.
DOI: https://doi.org/10.1007/s10905-023-09825-8

Interpretive Summary: The learning abilities for honey bees, bumble bees, and stingless bees have been demonstrated through experiments that train bees to associate flower odors with a reward, such as sugar solution. This is referred to as simple conditioning. Social bees (i.e., those that live in colonies as do honey bees) have a natural tendency to extend their tongues (called proboscises) when their antennae are touched with a droplet of sugar solution. This response is known as the proboscis extension reflex (PER). However, PER is not portrayed by solitary bees, which are those that do not live a colony setting. Here we employ a newly developed, passive conditioning protocol that we previously used successfully with solitary bees to show that they can learn that an odor signals the presence of a reward. In this study, we wanted to demonstrate that the solitary bees can be trained to tell the difference between two odors, only one of which signals the presence of a reward. We tested two managed cavity-nesting bees, Osmia lignaria and Megachile rotundata. We found that both females and males of O. lignaria were better than M. rotundata adults at learning which odor meant a reward was present. We also found no instinctive preference for any of the three odors that we tested, meaning that none of the odors were naturally attractive to the bees. Use of this kind of training and testing for some solitary bees may help us to learn more about bee behavior and motivation, bee preferences for certain flowers, and whether pesticides can impair bee ability to learn and remember odors in their environment. This work highlights that not all bee species respond the same way and that more research is needed for finding tools and techniques for examining bee learning abilities.

Technical Abstract: Sensory abilities and cognitive processes for honey bees, bumble bees, and stingless bees have been demonstrated through conditioning experiments using odor as a conditioned stimulus (CS) and sugar solution as an unconditioned stimulus (US). Social bee conditioning employs the proboscis extension reflex (PER) to elicit an innate response to sucrose solution. However, solitary bees fail to reliably exhibit PER in response to touching antennae or tarsi with sugar solution. Here we employ a newly estab-lished, conditioning protocol for unrestrained solitary bees, i.e., the commercially available Osmia lignaria and Megachile rotundata, that allows them to explore a rearing chamber in which training can occur to sub-sequently reveal the ability to discriminate between an odor associated with sugar-water and a different odor associated with no reward, using three different odor pairings. No innate preference for any trial odor was found for either species. Osmia lignaria females and males clearly showed the ability to discriminate between odors after conditioning; M. rotundata adults demonstrated discrimination learning in only one set of odor pairings. Laboratory assays to condition solitary bees to not only associate odor with reward but to also discriminate between odors could sup-port studies that address bee behavior and motiva-tion, bee floral specialization or flower constancy, and sublethal effects of environmental stressors on bee performance. The discrepancy we found in spe-cies responses highlights the need for comparative studies, because there is no one-size-fits-all protocol for examining cognitive and learning abilities of the many species of bees whose life histories and experi-ences influence their behavior.