Separation of different pollen types by chemotactile sensing in Bombus terrestris

When tasting food, animals rely on chemical and tactile cues, which determine the animal's decision on whether to eat food. As food nutritional composition has enormous consequences for the survival of animals, food items should generally be tasted before they are eaten or collected for later consumption. Even though recent studies have confirmed the importance of, for example, gustatory cues, compared with olfaction only little is known about the representation of chemotactile stimuli at the receptor level (let alone higher brain centers) in animals other than vertebrates. To better understand how invertebrates may process chemotactile cues, we used bumblebees as a model species and combined electroantennographical (EAG) recordings with a novel technique for chemotactile antennal stimulation in bees. The recorded EAG responses to chemotactile stimulation clearly separated volatile compounds by both compound identity and concentration, and could be successfully applied to test the receptor activity evoked by different types of pollen. We found that two different pollen types (apple and almond; which were readily distinguished by bumblebees in a classical conditioning task) evoked significantly distinct neural activity already at the antennal receptor level. Our novel stimulation technique therefore enables investigation of chemotactile sensing, which is highly important for assessing food nutritional quality while foraging. It can further be applied to test other chemosensory behaviors, such as mate or nest mate recognition, or to investigate whether toxic substances, e.g. in pollen, affect neuronal separation of different food types.