Pollen Elicits Proboscis Extension but Does not Reinforce PER Learning in Honeybees.

Elizabeth Nicholls,Natalie De Ibarra

doi:10.3390/insects4040542

Abstract

The function of pollen as a reward for foraging bees is little understood, though there is evidence to suggest that it can reinforce associations with visual and olfactory floral cues. Foraging bees do not feed on pollen, thus one could argue that it cannot serve as an appetitive reinforcer in the same way as sucrose. However, ingestion is not a critical parameter for sucrose reinforcement, since olfactory proboscis extension (PER) learning can be conditioned through antennal stimulation only. During pollen collection, the antennae and mouthparts come into contact with pollen, thus it is possible that pollen reinforces associative learning through similar gustatory pathways as sucrose. Here pollen was presented as the unconditioned stimulus (US), either in its natural state or in a 30% pollen-water solution, and was found to elicit proboscis extension following antennal stimulation. Control groups were exposed to either sucrose or a clean sponge as the US, or an unpaired presentation of the conditioned stimulus (CS) and pollen US. Despite steady levels of responding to the US, bees did not learn to associate a neutral odour with the delivery of a pollen reward, thus whilst pollen has a proboscis extension releasing function, it does not reinforce olfactory PER learning.

Highlights

The neural pathways underlying learning with sucrose rewards are well understood
Unlike sucrose solutions or nectar, pollen is not ingested by foraging bees, raising the question of how pollen could act as a reward for learning floral cues
Whilst evidence exists to suggest that foraging bees are capable of associating both visual and olfactory stimuli with pollen reward, its reinforcing properties remain unknown

Summary

Introduction

The neural pathways underlying learning with sucrose rewards are well understood. The sucrose reward resembles floral nectar rewards collected by bees whilst visiting flowers, and the ecological validity of such experimental work has been widely accepted [7±9]. Pollen is often assumed to be perceived by bees as a reward of varying profitability, based on the differences in protein and amino acid content between pollen from different plant species [10±13]. Bees form preferences for particular pollen types [14±17], it is still unknown how these preferences are formed and what bees might learn during pollen collection. Unlike sucrose solutions or nectar, pollen is not ingested by foraging bees, raising the question of how pollen could act as a reward for learning floral cues

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Conclusion