Resource profitability, but not caffeine, affects individual and collective foraging in the stingless beePlebeia droryana

Abstract

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.

Foragers of the stingless bee Plebeia droryana inform nestmates about the direction, but not the distance to food sources

“…Foragers from the tested colonies were trained to artificial feeders by standard training procedures (see von Frisch, 1967;Peng et al, 2019Peng et al, , 2020. First, we placed one artificial feeder with a 50% sucrose solution next to the nest entrance to attract foragers to start collecting the sucrose solution.…”

“…In Plebeia droryana, a small (∼3 mm long) species commonly found in South America, foragers have been shown to produce buzzing sounds to alert nestmates about the presence of a food source, but Kerr (1958, 1960) found no evidence for specific location communication in this species. Peng et al (2019), on the other hand, found that the number of P. droryana foragers steadily increased over time at a high-quality food source, suggesting that P. droryana foragers might provide nestmates with specific location information. The two studies differed in both the number of colonies observed and the foraging distance tested.…”

Octopamine increases individual and collective foraging in a neotropical stingless bee

“…Honeybees (Apini) and stingless bees (Meliponini) separated about 80 Mya [17] and have evolved many complex social traits independently. The two groups vary considerably in their division of labour [18], their recruitment communication [19] and stingless bees differ from honeybees in how they respond to some neuroactive chemicals [20]. This raises the question whether OA plays similar roles in stingless bees as in honeybees.…”

“…We tested the prediction that OA increases short-term foraging effort in the common Brazilian stingless bee Plebeia droryana. This would lead to an increased foraging tempo as well as potentially promoting the recruitment behaviour in P. droryana [20]. We manipulated wild P. droryana colonies to assess OA effects in the natural environment of this species.…”

Nectar non-protein amino acids (NPAAs) do not change nectar palatability but enhance learning and memory in honey bees

“…Also, their impact on pollinators' health and cognition is both species-and dose-dependent [19][20][21][22][23][24]. Despite the relevance that nectar SMs appear to have in plant-pollinator interactions, research on their ecological function is only limited to few alkaloids, a phenolic and a glycoside [15,[19][20][21][25][26][27] whereas the role of other common SMs has been mostly overlooked.…”