Correlation between octopaminergic signalling and foraging task specialisation in honeybees.

Regulation of pollen and nectar foraging in honeybees is linked to differences in the sensitivity to the reward. Octopamine (OA) participates in the processing of reward-related information in the bee brain, being a candidate to mediate and modulate the division of labour among pollen and nectar foragers. Here we tested the hypothesis that OA affects the resource preferences of foragers. We first investigated whether oral administration of OA is involved in the transition from nectar to pollen foraging. We quantified the percentage of OA-treated bees that switched from a sucrose solution to a pollen feeder when the sugar concentration was decreased experimentally. We also evaluated if feeding the colonies sucrose solution containing OA increases the rate of bees collecting pollen. Finally, we quantified OA and tyramine (TYR) receptor genes expression of pollen and nectar foragers in different parts of the brain, as a putative mechanism that affects the decision-making process regarding the resource type collected. Adding OA in the food modified the probability that foragers switch from nectar to pollen collection. The proportion of pollen foragers also increased after feeding colonies with OA-containing food. Furthermore, the expression level of the AmoctαR1 was upregulated in foragers arriving at pollen sources compared with those arriving at sugar-water feeders. Using age-matched pollen and nectar foragers that returned to the hive, we detected an upregulated expression of a TYR receptor gene in the suboesophageal ganglia. These findings support our prediction that OA signalling affects the decision in honeybee foragers to collect pollen or nectar.

Resource profitability, but not caffeine, affects individual and collective foraging in the stingless bee Plebeia droryana.

Plants and pollinators form beneficial relationships, with plants offering resources in return for pollination services. Some plants, however, add compounds to nectar to manipulate pollinators. Caffeine is a secondary plant metabolite found in some nectars that affects foraging in pollinators. In honeybees, caffeine increases foraging and recruitment to mediocre food sources, which might benefit the plant, but potentially harms the colonies. For the largest group of social bees, the stingless bees, the effect of caffeine on foraging behaviour has not been tested yet, despite their importance for tropical ecosystems. More generally, recruitment and foraging dynamics are not well understood in most species. We examined whether caffeine affects the foraging behaviour of the stingless bee Plebeia droryana, which frequently visits plants that produce caffeinated nectar and pollen. We trained bees to food sources containing field-realistic concentrations of sugar and caffeine. Caffeine did not cause P. droryana to increase foraging frequency and persistence. We observed P. droryana recruiting to food sources; however, this behaviour was also not affected by caffeine. Instead we found that higher sugar concentrations caused bees to increase foraging effort. Thus, unlike in other pollinators, foraging behaviour in this stingless bee is not affected by caffeine. As the Brazilian P. droryana population that we tested has been exposed to coffee over evolutionary time periods, our results raise the possibility that it may have evolved a tolerance towards this central nervous system stimulant. Alternatively, stingless bees may show physiological responses to caffeine that differ from those of other bee groups.