Pollen phenolics and regulation of pollen foraging in honeybee colony

Abstract

Honeybee colonies can regulate their collection of pollen in response to pollen stores within the hive. The question as to how colonies or individual foragers detect changes in pollen quantity or quality is intriguing. Although forager bees seem unable to directly assess pollen protein content, other nonnutritional factors (particularly changes in pollen odor) may act as cues for assessing pollen stores. Pollen is enriched with nonnutritional phenolic compounds, which are responsible for the strong pollen odor to which honeybees are sensitive and which are also plant-defensive compounds against herbivores. Here we examine the bees' foraging activity for pollen of different floral species in relation to their phenolic contents. We show that honeybee foragers of Apis cerana prefer species with low phenolic content, thus suggesting that they can detect and estimate the amount of phenolics in pollen. Furthermore, feeding colonies with sugar syrup seems to increase their acceptance of pollen with high phenolic contents. When such feeding was stopped, a decrease in the collection of pollen with high phenolic content was observed, which was accompanied by an increase in the collection of pollen with low phenolic content. This shift resulted in a reduction of the overall phenolic intake rate a few days after colony manipulation. These results suggest that pollen-foraging activities of a honeybee colony are regulated by quantitative changes in phenolic contents of pollen. Honeybees could, therefore, use nonnutritional factors, such as pollen phenolics, to assess colony requirements and to change foraging dynamics accordingly.