Modification of the Innate Antennal Reaction at Floral Guides in Experienced Bumblebees, Bombus terrestris (Hymenoptera: Apidae)

Abstract

The first physical contact with flowers by flower-naive bumblebees of the species Bombus terrestris (Linnaeus 1758) is a touch with the tips of their antennae prior to landing. Naive bumblebees perform this innate antennal reaction either at the margin of flowers or at small coloured floral guides. LUNAU [1992] hypothesised that the antennal reaction aims at the perception of substances on floral tissues through chemoreception. In order to test the effect of experience with distinct flower guides on the antennal reaction learning experiments were performed with worker bumblebees of the species Bombus terrestris. A choice of two types of artificial flowers was presented simultaneously: (1) Blue artificial flowers with a small central yellow colour mark, offering 7 μl of 50% sucrose solution, and (2) blue artificial flowers with a small central brown colour mark, offering 7 μl of 10% sucrose solution. The antennal reaction of individuals was monitored at two different phases in the experiment: (1) During the first 90 approaches, and (2) after 300 approaches to artificial flowers. Unexpectedly it was found that experienced bumblebees showed the antennal reaction significantly more often at the small central colour mark than less experienced ones. During flight, bumblebees retained the antennae in a position characterised by a distance between the antennal tips of more than 5 mm and by an angle between the antennal flagella of more than 90°. Prior to antennal contact with the artificial flower experienced bumblebees reduced the distance between the antennal tips to about 5 mm, which corresponds to the diameter of the central colour mark. This adjustment was not dependent on the presence of scent-marks. It is suggested that bumblebees benefit from their antennal reaction at flowers by remote sensing of pollen reward and consequential avoidance of waste of energy by landing and restarting from the flower.