Aggressive and Docile Colony Defence Patterns in Apis mellifera. A Retreater–Releaser Concept
Gerald Kastberger
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Ronald Thenius
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Anton Stabentheiner
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Randall Hepburn
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R. Hepburn Department of Zoology, Rhodes University
, Grahamstown,
South Africa
Colony defence in Apis mellifera involves a variety of traits ranging from 'aggressive' (e.g. entrance guarding, recruitment of flying guards) to 'docile' (e.g. retreating into the nest) expression. We tested 11 colonies of three subspecies (capensis, scutellata, carnica) regarding their defensiveness. Each colony was selected as reportedly 'aggressive', 'intermediate' or 'docile' and consisted of about 10,000 bees. We applied three stimulation regimes (mechanical disturbance, exposure to alarm pheromones, and the combination of both) and measured their behaviours by tracking the rates of outflying bees at the entrance sites of the test hives. We provided evidence that for mechanical disturbances the test colonies resolved into two response types, if the 'immediate' defence response, assessed in the first minute of stimulation, was taken as a function of foraging: 'releaser' colonies allocated flying guards, 'retreater' colonies reduced the outside-hive activities. This division was observed irrespective of the subspecies membership and maintained in even roughly changing environmental conditions. However, if pheromone and mechanical stimulation were combined, the variety of colony defensiveness restricted to two further types irrespective of the subspecies membership: six of nine colonies degraded their rate of flying defenders with increasing foraging level, three of the colonies extended their 'aggressiveness' by increasing the defender rate with the foraging level. Such 'super-aggressive' colonies obviously are able to allocate two separate recruitment pools for foragers and flying defenders.
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An elaborate defence system in both open-nesting (Seeley et al. 1982; Kastberger et
al. 2007) and cavity dwelling species (Ruttner 1988) of honeybees has evolved in
tandem with the attractiveness of honeybee colonies and their nests as food resources
for predators. In particular, the honeybees have to run a cunning trading-off
regarding the two poles of work loads, foraging and defending, to efficiently collect
and minister the pollen and honey resources and to safeguard the nest in order to
minimize losses and expenses. The main goal of defence is therefore to make the
nest site a zone of shelter for colony members as well as a zone of high risk for
predators for which the entry fee has to be set as high as possible.
Nonetheless, there is considerable variation in the defence systems among and
within honeybee species (Kerr 1967; Winston 1992; Boch and Rothenbuhler 1974;
Winston 1987; Moritz et al. 1987; Moritz and Southwick 1992; Page et al. 1995;
Seeley et al. 1982), even in colonies headed by related queens kept under the same
conditions in the same apiary (Collins et al. 1980, 1984, 1988; Schneider and
McNally 1992; Page et al. 1995; Stort 1974, 1975a, b; Villa 1988). Generally,
variability in defensiveness in honeybees is caused by internal and external factors
(Schua 1952; Woyke 1992; Collins 1981; Brandeburgo et al. 1982; Southwick and
Moritz 1987; Collins and Rinderer 1985; Breed et al. 2004) and ranges from extreme
docility to extreme aggressiveness.
Docile strategies in honeybees can be defined as being generally non-stinging
and avoiding exposure to the predator. In this context, the workers of
cavitydwelling species, Apis mellifera and A. cerana, respond to some threats by reduction
or even ceasing the outside-hive activities. Staying at the nest under threat has also
the advantage of having a sufficiently big stock for collective defence. The
phylogenetically older free-nesting Giant honeybees A. dorsata also exhibit docile
traits that effectively repel wasp predators (Kastberger et al. 2007) by colony
members on the curtain surface, which stay at the nest and show synchronized
abdominal shaking. In A. mellifera, docility is reported to be associated with low
ambient temperature, low ambient humidity (Schua 1952; Collins 1981; Drum and
Rothenbuhler 1984), small colony size (Boch and Rothenbuhler 1974; Collins et al.
1982; Collins and Kubasek 1982), low honey store size and good nectar flows in the
field (Winston 1987).
The aggressive strategies of honeybees comprise guarding and soldier behaviour
(Breed et al. 1990, 2004; Stabentheiner et al. 2002, 2007) in diverse facets.
According to conventional terminology, guard bees patrol the entrance of the colony as
well as the periphery of the nest in open colonies. The main purpose of guarding is to
identify and remove foreign conspecific intruders (Breed et al. 1992). However, guard
bees may also play a role in recruiting other bees to defend against larger intruders
(Moore et al. 1987). Such non-guard defenders are mobilised and released particularly
in masses to repel intruders in counter-attacking operations. The term soldier bees
(Breed et al. 2004) is appropriate to designate bees that p (...truncated)