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' (Bombus terrestris) 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.