Different solutions by bees to a foraging problem

Honeybees (Apis mellifera) were used as a model insect system to explore how foragers solve problems involving cost as well as reward. Reward difference was created by varying sucrose molarity, whereas cost difference was created by varying flower-handling time in artificial flower patches. Unlike earlier work, flower-handling time was a function of stamen length rather than corolla length, such that longer stamens increased flower-handling time. When changing from short- to long-stamen flowers, access to nectar becomes limited to specific routes, which differ in difficulty. Experiments were performed with 2 mu l and 6 mu l sucrose rewards. Differences in reward and/or handling time were associated with flower colour difference (blue versus white flowers). Higher energy reward (2 M) and shorter handling time were preferred by bees when foraging problems involved only a reward or a handling-time difference, which followed energy maximization expectations. However, when the two variables were combined so that greater handling time was combined with higher reward, behaviour differed between individuals. Some bees made choices based solely on reward, some only on effort (handling time), and some simply on flower colour. These results contrast with early work where handling time was a function of corolla length and all bees avoided longer corollas. Results suggest that honeybees do not always behave as predicted by simple energy maximization principles; rather, individuality in choice arises when the foraging problem becomes more difficult because of increased complexity (dimensionality) of the problem. (C) 2009 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.