Gustatory sensitivity to amino acids in bumblebee mouthparts

Bees rely on amino acids from nectar and pollen for essential physiological functions. While nectar typically contains low (less than 1 mM) amino acid concentrations, levels in pollen are higher but variable (10-200 mM). Behavioural studies suggest bumblebees have preferences for specific amino acids but whether such preferences are mediated via gustatory mechanisms remains unclear. This study explores bumblebees' (<i>Bombus terrestris</i>) gustatory sensitivity to two essential amino acids found in nectar and pollen, valine and lysine, using electrophysiological recordings from gustatory sensilla on their mouthparts. Valine elicited a concentration-dependent response from 0.1 mM, indicating that bumblebees could perceive valine at concentrations found naturally in nectar and pollen. By contrast, lysine failed to evoke a response across tested concentrations (0.1-500 mM). The absence of lysine detection raises questions about the specificity and diversity of amino acid-sensitive receptors in bumblebees. Bees responded to valine at lower concentrations than sucrose, suggesting comparatively higher sensitivity (EC₅₀: 0.7 mM versus 3.91 mM for sucrose). Our findings indicate that bumblebees can evaluate the amino acid content of pollen and nectar using pre-ingestive cues, rather than relying on post-ingestive cues or feedback from their nestmates. Such sensory capabilities probably impact foraging strategies, with implications for plant-bee interactions and pollination.