Effects of octopamine on memory retention under chemical stress: a behavioral study on honey bees

Abstract

Honey bees may experience the adverse effects of environmental contaminants when exposed during foraging trips, or something to that effect. We hypothesized that octopamine (OA), with important functions in reward signaling and learning, can improve the behavior of honey bees under chemical stress. Memory retention and sucrose responsiveness were evaluated using the proboscis extension reflex (PER) assay. The one-day-old bees were exposed separately to diazinon, imidacloprid, paraquat, manganese, and thymol at concentrations of 0.22, 29.04, 55.69, 106.19, and 0.91 ppm, respectively. On the 21st day of exposure, the bees’ responses to memory retention and sucrose responsiveness experiments were recorded after the training trial. In addition, PERs were recorded after OA injection. During the intervals, honey bees were exposed to the toxins topically. The expression levels of OA receptor genes, AmoctαR1 and AmoctβR4, were measured. The sucrose responsiveness tests showed no significant differences between the bees stimulated with the control solutions or toxins. Moreover, our results indicated that memory retention significantly declined in honey bees exposed to toxins compared to the controls (P ≤ 0.05). According to the findings, OA improved the memory retention of honey bees exposed to toxins (P ≤ 0.05). The expression levels of AmoctαR1 and AmoctβR4 genes significantly increased in the treated honey bees, especially those exposed to paraquat and manganese, after 30 min post-OA injection. It can be concluded that under chemical stress, OA administration encouraged honey bees to respond to a stimulus. Therefore, it can be added to a nutrient-enriched diet.