Drifting of workers in nest aggregations of the giant honeybee Apis dorsata

Apidologie, Nov 2002

Jürgen Paar, Benjamin P. Oldroyd, Ernst Huettinger, Gerald Kastberger

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Drifting of workers in nest aggregations of the giant honeybee Apis dorsata

Apidologie Drifting of workers in nest aggregations of the giant honeybee Apis dorsata Jürgen PAAR 0 2 Benjamin P. OLDROYD 2 Ernst HUETTINGER 1 KASTBERGER 0 0 Institute of Zoology, Karl-Franzens University Graz , Universitätsplatz 2 8010 Graz , Austria 1 BFL-Institute of Apiculture , 3293 Lunz , Austria 2 School of Biological Sciences, A12, University of Sydney , 2006 NSW , Australia - The extent of worker drifting between nests in aggregations of colonies of the giant Asian honeybee Apis dorsata was studied using DNA microsatellites. Four aggregations with three, six, seven and eight colonies were sampled. 1537 workers were genotyped using four loci. Maternity testing was used to separate drifted and natal workers, and to assign drifted individuals to their actual maternal colony. The proportion of drifted workers ranged from 0 to 6.25% with an average of 1.27% (sd = 0.245). No significant differences in rates of drifting were found between the four aggregations. There was also no correlation between the direction of the drift and the position of the nests relative to each other. These results show that in A. dorsata, a bee species that frequently nests in dense aggregations, the extent of forager drifting between colonies can be very low. 1. INTRODUCTION D r i f t i n g o f f o r a g e r s a n d d r o n e s i s a well-known phenomenon in Apis mellifera L. (e.g. Betts, 1932; Free, 1958) . During drifting events, foragers return to the wrong colony due to orientation errors (Rauschmayer, 1928), where they must then be accepted by the guard bees. Acceptance rates vary. When colonies are nutritionally stressed, and robber bees are about, very few foreign bees are admitted to colonies, but when conditions are favourable, drifted bees are usually accepted (Downs and Ratnieks, 2000) . In apiaries of Apis mellifera the degree of drifting depends on a variety of environmental and apiary layout factors. Hive orientation with respect to the sun and prevailing wind can influence direction and level of drift (Jay, 1965, 1971; Moritz and Neumann, 1996) . Placing colonies in long rows with little space between and few markings on or between colonies can cause confusion among returning foragers, a large proportion of which return to the wrong colony. Under these extreme circumstances, 50–90% of foragers can move from their natal nest to neighbouring nests, depleting the foraging populations from colonies situated in the middle of the rows, and greatly increasing those of the colonies located at the ends (Free and Spencer-Booth, 1961; Jay, 1965, 1966; Pfeiffer and Crailsheim, 1998) . However, if colonies are arranged in small clusters around conspicuous land marks, with random entrance orientations, or other appropriate apiary layouts, rates of drifting are much lower – around 5% (Neumann et al., 2000). Drifting of foragers between natural colonies is not expected because it is likely to reduce colony fitness (Jay, 1969a, b; Robinson, 1979; Goodwin et al., 1994) . First, colonies that receive foragers from other colonies may become exposed to contagions from other colonies (Jay, 1968; Matheson, 1984; Sakofski, 1990; Boylan et al., 1991; Rath et al., 1991; Goodwin et al., 1993, 1994) , though they may benefit from an increased forager force. Second, kin selection arguments suggest that it is mal-adaptive for workers to forage for unrelated colonies. Finally, honey bees frequently rob the colonies of their con-specifics. Thus there is a strong chance that a forager arriving from another colony will be mistaken for a robber and expelled or killed (Downs et al., 2001). Taken together, it is somewhat surprising that A.mellifera foragers are so prone to drifting between colonies. This suggests that drifting is an artefact of artificial aggregations in apiaries. In the wild, colonies of A. mellifera are either found singly, or in loose aggregations in which colonies are separated by many meters both vertically and horizontally (Oldroyd et al., 1995; McNally and Schneider, 1996) , suggesting that in the wild, foragers would rarely drift. Unlike the rather loose aggregations sometimes found in A. mellifera the giant Asian honeybee Apis dorsata Fabr. regularly forms extremely dense aggregations of colonies. Up to 200 colonies may occur in a single tree (Oldroyd et al., 2000) and the combs are often separated by only a few centimetres. Despite observations of short range swarming – ‘budding’ – (Lindauer, 1956) and home site fidelity of swarms after their seasonal migration (Neumann et al., 2000; Paar et al., 2000) colonies within aggregations do not seem to be closely related (Oldroyd et al., 2000; Paar et al., unpublished data) . The single combs of A. dorsata are attached to tree branches, cliff overhangs or buildings and so are completely exposed on all sides. Thus A. dorsata colonies would appear to be particularly vulnerable to conspecific robbing, and to the spread of pathogens and parasites amon (...truncated)


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Jürgen Paar, Benjamin P. Oldroyd, Ernst Huettinger, Gerald Kastberger. Drifting of workers in nest aggregations of the giant honeybee Apis dorsata, Apidologie, 2002, pp. 553-561, Volume 33, Issue 6, DOI: doi:10.1051/apido:2002040