Separation of different pollen types by chemotactile sensing in Bombus terrestris.

Abstract

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.

Pollen, anther, stamen, and androecium mimicry

“…PASAM structures are potentially multimodal signals including visual, olfactory, gustatory and tactile stimuli, but their chemical properties have only rarely been studied (Ruedenauer et al . 2017; Wilmsen et al . 2017).…”

“…Plant-parasitic fungi are known to stimulate host plants to produce pseudoflowers presenting pseudopollen (Ngugi & Scherm 2006). PASAM structures are potentially multimodal signals including visual, olfactory, gustatory and tactile stimuli, but their chemical properties have only rarely been studied (Ruedenauer et al 2017;Wilmsen et al 2017).…”

Do honeybees (Apis mellifera) differentiate between different pollen types?

“…olfaction) and/or pollen taste (i.e. their sensitivity to chemotactile cues) as cues to distinguish between different types of pollen [ 14 , 21 , 27 , 28 ]. Honeybees ( Apis mellifera ) can learn floral patterns, shapes and colors of different plant species and foraging decisions are often based on such visual cues [ 14 , 29 , 30 ].…”

“…Honeybees can also discriminate between many different odors [ 31 – 33 ] and thus various floral scents [ 34 , 35 ], for example field-bean ( Vicia faba , Fabaceae) and oilseed-rape ( Brassica napus , Brassicaceae) pollen scent [ 36 ]. They may also use taste/gustatory receptors on the distal segment of their antennae, their mouthparts and the tarsi of their forelegs to perceive water, sugars, salt and possibly other nutrients [ 28 , 37 ]. Because it is still unknown whether taste reception via touch is primarily chemical, tactile or a mix of both, we generally refer to taste or gustatory cues as chemotactile cues.…”

“…the currently “best” pollen type directly in the field. Moreover, several studies (reviewed in [ 14 ]) indicate that honeybees are, just like bumblebees [ 27 , 28 ], able to assess pollen nutritional quality.…”