Gustatory sensitivity to amino acids in bumblebees

Abstract

Bees rely on amino acids obtained from nectar and pollen for essential physiological functions, including maintenance, sexual maturation, and larval development. While amino acid concentrations in nectar are typically low (<1 mM), pollen contains higher levels (10-200 mM), with the exact concentrations varying by plant species. Behavioural studies suggest bumblebees have preferences for specific amino acids, yet whether such preferences are mediated pre-ingestively via gustatory mechanisms remains unclear. This study explores bumblebees' (Bombus terrestris) gustatory sensitivity to two essential amino acids (EAAs), valine and lysine, using electrophysiological recordings from gustatory sensilla on their mouthparts. Valine elicited a concentration-dependent response, with spikes produced from 0.1 mM and reaching an asymptote at 5 mM, indicating that bumblebees could perceive valine at the concentrations found naturally in nectar and pollen. In contrast, lysine failed to evoke spiking responses 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 to amino acids (EC50: 0.7 mM vs. 3.91 mM for sucrose). Our findings indicate that bumblebees are able to rapidly evaluate the amino acid content of pollen and nectar while foraging from flowers 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. Future research should explore bumblebees' response to other amino acids in isolation and combination, and mechanisms for detecting pollen-bound nutrients.