Longer tongues and swifter handling: why do more bumble bees (Bombus spp.) than honey bees (Apis mellifera) forage on lavender (Lavandula spp.)?
2013
BALFOUR, NICHOLAS J. | GARBUZOV, MIHAIL | RATNIEKS, FRANCIS L.W.
Lavender (Lavandula spp.) flowers attract more bumble bees (Bombus spp.) than honey bees (Apis mellifera). Counts of bees foraging on Lavandula × intermedia ‘Grosso’ at the University of Sussex campus, showed that bumble bees (92%) greatly outnumbered honey bees (8%). This was not due to a scarcity of honey bees, as the reverse ratio (94% honey bees vs. 6% bumble bees) occurred on borage (Borago officinalis) at the same location. Video analysis of free‐flying bees revealed that all bumble bee species present (Bombus terrestris/lucorum, Bombus pascuorum, and Bombus lapidarius) handled lavender flowers three times faster than honey bees (mean extraction times: 0.38, 0.37, 0.34 s respectively, vs. 1.30 s; all P < 0.001). Honey bee tongue length (6.6 mm) was approximately 2 mm shorter than those of bumble bees (7.8–8.9 mm) and 1 mm shorter than the lavender corolla tube (c. 7 mm). In addition, bumble bees probed twice as many lavender flowers encountered than honey bees (86% vs. 46%). Experimentally reducing effective corolla tube length with scalpel incisions significantly decreased extraction time for honey bees (from 1.11 to 0.76 s; P < 0.001) but not for bumble bees (0.33 to 0.28 s; P = 0.266). Results suggest that honey bees are deterred from foraging on lavender because they are being outcompeted by bumble bees, which forage more efficiently.
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