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 (<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. In 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
vs. 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 likely impact foraging strategies,
with implications for plant-bee interactions and pollination.