Foraging distance in Bombus terrestris L. (Hymenoptera: Apidae)

Apidologie, Jun 2008

Stephan Wolf, Robin F.A. Moritz

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Foraging distance in Bombus terrestris L. (Hymenoptera: Apidae)

Apidologie Foraging distance in Bombus terrestris L. (Hymenoptera: Apidae)* Stephan Wol 0 Robin F.A. Moritz 0 0 Institut für Biologie / Institutsbereich Zoologie, Martin-Luther-Universität Halle-Wittenberg , Germany 1 Manuscript editor: Jacqueline Pierre - A major determinant of bumblebees pollination efficiency is the distance of pollen dispersal, which depends on the foraging distance of workers. We employ a transect setting, controlling for both forage and nest location, to assess the foraging distance of Bombus terrestris workers and the influence of environmental factors on foraging frequency over distance. The mean foraging distance of B. terrestris workers was 267.2 m ± 180.3 m (max. 800 m). Nearly 40% of the workers foraged within 100 m around the nest. B. terrestris workers have thus rather moderate foraging ranges if rewarding forage is available within vicinity of the nests. We found the spatial distribution and the quality of forage plots to be the major determinants for the bees foraging decision-making, explaining over 80% of the foraging frequency. This low foraging range has implications for using B. terrestris colonies as pollinators in agriculture. 1. INTRODUCTION Pollen dispersal through animal pollinators is essential for plant reproduction. The efficiency of pollinators depends on various factors including the number of individuals that carry pollen from one flower to another, the number of pollen grains actually transferred on the flower, and the distance over which pollen is transferred. The latter is of particular importance with respect to rare and widely dispersed plants (e.g. Kwak et al., 1998) but also for the pollination service in agriculture. Bumblebees (Bombus spp.) are regarded as most efficient pollinators, not only for the pollination of wild flowers but also for pollination services, used in both outdoor and greenhouse horticulture and orchards (e.g. Morandin et al., 2001a, b; Dasgan et al., 2004; Velthuis and van Doorn, 2006) . They have been shown to be able to out-compete honeybees (Apis mellifera) in individual workers pollination efficiency (Gauld et al., 1990; Westerkamp, 1991; Wilson and Thomson, 1991; Goulson, 2003) . This is partly due to the more robust handling of flowers by bumblebees and their ability of buzz-pollination (e.g. in tomatoes) (Kevan et al., 1993; Morandin et al., 2001a,b; Goulson, 2003) but also due to fundamental differences in foraging strategies. Foraging Apis workers take advantage of their very sophisticated communication system, which allows efficient recruitment of large numbers of foragers to highly rewarding sites to exploit these in short time. The communication in bumblebees, however, is much less advanced and only the type of resource but not its position is communicated (Dornhaus and Chittka, 1999, 2001, 2004) . Therefore, Bombus workers primarily forage based on individual experience and colonies have more scattered forage grounds (Westerkamp, 1991; Kearns and Thomson, 2001; Goulson, 2003) . In commercial use, the foraging range determines the optimal density of bumblebee colonies for facilitating pollination services. The foraging distance of workers has, therefore, been the research focus of many studies. Walther-Hellwig and Frankl (2000a) estimated a maximum foraging distance for Bombus terrestris of up to 1750 m in a mark and recapture study along a transect. They found the majority of the workers (75%) foraging in distances of less then 1500 m from the nest, and 43% of the foragers were found within a radius of 500 m. Other studies, also relying on transects but assigning B. terrestris workers genetically to common colonies, obtained much smaller maximum foraging distances of 758 m (Knight et al., 2005) or even less than 625 m (Darvill et al., 2004) . Estimates based on a range of assumed colony densities and genetic colony assignment (Chapman et al., 2003) resulted in a maximum foraging distances ranging from 870– 3900 m for B. terrestris workers. Obviously estimates of foraging ranges have one aspect in common: they are highly variable. They range from a few hundred meters to several kilometres, which is not particularly satisfactory given the high significance of bumblebees as commercial and natural pollinators. It is unclear to what extent the high variance among previous studies reflects differences among the studied colonies or resulted from different experimental approaches. Also, variable climate and weather conditions among studies are bound to generate additional variance for foraging distance. Finally, plant density is one of the most important factors for foraging distances. If forage is sparse, bees must fly much farther for rewarding food plants than in a setting with high plant density (Heinrich, 1976) . Here we study foraging flight distances of B. terrestris workers by choosing an experimental design that provided, for the first time, full control of the external factors by contro (...truncated)


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Stephan Wolf, Robin F.A. Moritz. Foraging distance in Bombus terrestris L. (Hymenoptera: Apidae), Apidologie, 2008, pp. 419-427, Volume 39, Issue 4, DOI: doi:10.1051/apido:2008020