Negative Incentive Contrast Induces Economic Choice Behavior by Bumble Bees

Abstract

A negative incentive contrast experiment was conducted to determine whether responses to a reward reduction facilitate adaptive decisions by bumble bee (Bombus impatiens) foragers. In the acquisition phase of the experiment subjects were trained on blue targets (artificial flowers) that contained 50% (weight percent) or 20% sucrose solution and in the test phase subjects were given a choice between familiar targets and yellow targets that had either an economic profitability lower than, equal to, or higher than blue targets, where all targets contained 20% sucrose solution. Subjects trained to a low reward concentration showed a consistent preference for blue targets in the test phase of the experiment, while subjects that experienced a reward reduction exhibited a temporary disruption of consummatory behavior and developed preferences that reflected the profitability of targets. These results support a functional interpretation of responses to a reward reduction: incentive contrast induces foragers to visit alternative sources of nectar and, thereby, facilitates economical decisions. The choice behavior observed over the test phase suggests that associative processes then direct the formation of flower choices.