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)