Abstract
Generalist pollinators like the buff-tailed bumble bee, Bombus terrestris, encounter both nutrients and toxins in the floral nectar they collect from flowering plants. Only a few studies have described the gustatory responses of bees toward toxins in food, and these experiments have mainly used the proboscis extension response on restrained honey bees. Here, a new behavioral assay is presented for measuring the feeding responses of freely-moving, individual worker bumble bees to nutrients and toxins. This assay measures the amount of solution ingested by each bumble bee and identifies how tastants in food influence the microstructure of the feeding behavior.The solutions are presented in a microcapillary tube to individual bumble bees that have been previously starved for 2-4 hr. The behavior is captured on digital video. The fine structure of the feeding behavior is analyzed by continuously scoring the position of the proboscis (mouthparts) from video recordings using event logging software. The position of the proboscis is defined by three different behavioral categories: (1) proboscis is extended and in contact with the solution, (2) proboscis is extended but not in contact with the solution and (3) proboscis is stowed under the head. Furthermore the speed of the proboscis retracting away from the solution is also estimated.In the present assay the volume of solution consumed, the number of feeding bouts, the duration of the feeding bouts and the speed of the proboscis retraction after the first contact is used to evaluate the phagostimulatory or the deterrent activity of the compounds tested.This new taste assay will allow researchers to measure how compounds found in nectar influence the feeding behavior of bees and will also be useful to pollination biologists, toxicologists and neuroethologists studying the bumble bee's taste system.
Highlights
The reduced proboscis contact time and feeding bout frequency with water or the sucrose solution laced with quinine is interpreted here as a refusal to initiate further feeding on nonnutritive or potentially toxic solutions
When quinine is added to 1 M sucrose solution, bumble bees reduce the volume of solution they consume, they retract the proboscis faster, reducing contact time between the mouthparts and the solution containing a toxin
These results suggest that quinine is perceived by the gustatory receptor cells on the mouthparts of the bumble bee, as already previously identified in the honey bee[9]
Summary
The bumble bee species, Bombus terrestris (Linnaeus, 1758), is a generalist pollinator that visits the flowers of many plant species including those producing nectar containing toxins[6]. Bumble bees have been shown to avoid consuming solutions containing high concentrations of toxins in a 24 hr two-choice assay[7] This assay of food consumption described by Tiedeken et al.[7] revealed that bees can detect bitter compounds in solutions. This assay was unable to distinguish taste from post-ingestive processes such as malaise that could affect feeding behavior over this time interval[8,9,10]. The speed of the proboscis retraction is measured, as an indicator of an active avoidance, and preingestive detection
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