Behavioural discrimination of oilseed rape volatiles by the honeybee <i>Apis mellifera</i> L.

Abstract

This study investigated the ability of the honeybee to discriminate between six compounds previously identified as oilseed rape floral volatiles: linalool, 2-phenylethanol, methyl salicylate, benzyl alcohol, (E)-2-hexenal and 1-octen-3-ol. These components were tested individually or in a synthetic mixture for their ability to elicit the conditioned proboscis extension response. Three experiments were done: conditioning to the mixture at one concentration (1.0, 0.1 or 0.01 μg per component) and testing to the individual components either at the conditioning or at the other concentrations; conditioning to individual components and testing to the mixture (1.0 μg); conditioning and testing to the individual components (1.0 μg). The results from the proboscis extension assay were then compared to those obtained from free-flying bees in a flight room. From the conditioned proboscis extension assay, a conditioning threshold level was found (0.1 μg for the mixture studied) below which a reliable conditioning could not be achieved. Recognition thresholds were observed: bees responded to concentrations ten-fold higher or lower than that used for conditioning. Responses to lower concentrations were weaker, whilst responses were increased at concentrations higher than the conditioning one. A hierarchy within the compounds tested was found, with linalool, 2-phenylethanol and methyl salicylate cueing mixture recognition more effectively than the other components. The ranking order of the six components was similar in both the conditioned proboscis extension and the conditioned foraging behaviour in flight room. When conditioned and tested to the individual components, bees discriminated a learned odour from a number of others. However, the specificity level for the recognition of the learned odour varied according to the component, the most clearly discriminated being the compounds which were used by the bee in mixture recognition.