Sugar response and gustatory gene expression in the stingless bee Tetragonisca fiebrigi

Sugar detection and gustatory responsiveness are critical for foraging success in bees, influencing their ability to locate and exploit nectar and pollen sources. Here, we investigated the sugar response thresholds and the expression of two candidate gustatory receptor genes (TfieGr1 and TfieGr3) in the antennae and proboscises of foragers of the stingless bee Tetragonisca fiebrigi. Proboscis extension assays revealed that returning pollen foragers (PF) exhibited lower sugar response thresholds and higher sensitivity to sucrose, glucose, and fructose than returning nonpollen foragers (NPF), suggesting that NPF could be mainly engaged in finding high-quality nectar sources. In addition, more than 60 % of PF responded to all sugars tested, while NPF showed a strong preference for sucrose and glucose, with only 4 % responding to fructose. Molecular experiments revealed no significant differences in TfieGr1 and TfieGr3 expression levels between PF and NPF in either sensory tissue. These findings suggest that other gustatory receptors or mechanisms, such as central processing or internal nutrient sensing, may underlie the observed behavioral differences. Our results highlight potential species-specific adaptations in sugar detection mechanisms and underscore the importance of integrating behavioral, molecular, and ecological approaches to understanding foraging strategies in stingless bees.