Abstract In honeybees, as in other highly eusocial spe- cies, tasks are performed by individual workers, but se- lection for worker task phenotypes occurs at the colony level. We investigated the effect of colony-level selec- tion for pollen storage levels on the foraging behavior of individual honeybee foragers to determine (1) the rela- tionship between genotype and phenotypic expression of foraging traits at the individual level and (2) how geneti- cally based variation in worker task phenotype is inte- grated into colony task organization. We placed workers from lines selected at the colony level for high or low pollen stores together with hybrid workers into a com- mon hive environment with controlled access to resourc- es. Workers from the selected lines showed reciprocal variation in pollen and nectar collection. High-pollen- line foragers collected pollen preferentially, and low- pollen-line workers collected nectar, indicating that the two tasks covary genetically. Hybrid workers were not intermediate in phenotype, but instead showed direction- al dominance for nectar collection. We monitored the re- sponses of workers from the selected strains to changes in internal (colony) and external (resource) stimulus lev- els for pollen foraging to measure the interaction be- tween genotypic variation in foraging behavior and stim- ulus environment. Under low-stimulus conditions, the foraging group was over-represented by high-pollen-line workers. However, the evenness in distribution of the fo- cal genetic groups increased as foraging stimuli in- creased. These data are consistent with a model where task choice is a consequence of genetically based re- sponse thresholds, and where genotypic diversity allows colony flexibility by providing a range of stimulus thresholds. Key words Division of labor · Task performance · Selection · Pollen foraging · Honeybees Introduction Division of labor, whereby individuals within a social group specialize on different tasks, is one of the primary adaptations of sociality (Wilson 1971). Division of labor does not consist of a static allocation of workers to dif- ferent tasks. Instead, social insect colonies function in a dynamic environment that changes daily and seasonally. A key question, therefore, is how colonies regulate task organization in response to environmental change. One way that colonies may regulate task organization is via genotypic variation within the worker population (Robinson and Page 1989a; Bonabeau et al. 1996). A strong link between genotype and worker task prefer- ence has been established across social insect taxa (Calderone and Page 1988, 1991; Frumhoff and Baker 1988; Robinson and Page 1988, 1989b; Kolmes et al. 1989; Stuart and Page 1991; Oldroyd et al. 1992; Snyder 1993; O’Donnell 1996). Honeybee queens com- monly mate with 7–17 drones (reviewed by Page and Robinson 1991), generating genotypically diverse worker subfamily groups within the colony. If we assume that (1) these workers vary intrinsically in their thresholds of sen- sitivity to stimuli for a given task and (2) individuals per- form a task when the stimuli exceed their intrinsic thresh- old (the “stimulus threshold”), then genotypic diversity can generate division of labor. At low stimulus levels, a narrow subset of the colony performs the task. As stimu- lus levels for a task increase, individuals from other geno- typic subsets are recruited into the task group (Robinson and Page 1989a; Fewell and Page 1993). Thus, genotypic variation produces a subset of specialists for a given task (those with low thresholds), but allows the colony to re- spond flexibly to increased task stimuli. Communicated by R.F.A. Moritz J.H. Fewell ( ✉ ) Department of Biology, Arizona State University, Tempe, AZ 85287-1501, USA e-mail: j.fewell@asu.edu Tel.: +1-602-9656539, Fax: +1-602-9652519 R.E. Page Jr Department of Entomology, University of California, Davis, CA 95616, USA Behav Ecol Sociobiol (2000) 48:173–181 © Springer-Verlag 2000 ORIGINAL ARTICLE Jennifer H. Fewell · Robert E. Page Jr Colony-level selection effects on individual and colony foraging task performance in honeybees, Apis mellifera L. Received: 3 May 1999 / Received in revised form: 22 December 1999 / Accepted: 23 January 2000