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Tilia and bees
In article , P van
Rijckevorsel writes Stewart Robert Hinsley schreef There's always _Tilia tomentosa_ (from S.E. Europe) which is reported as killing (bumble) bees. One anecdote is that there were so many dead bees under the edge of one tree that there was a circular zone of enhanced soil fertility the next year. -- Stewart Robert Hinsley Well, carefull here. They cleared that up. The bees were not poisoned but died of hunger. Linden trees are especially popular late in the season when they are just about the only source of nectar. Nevertheless what nectar there is is not enough to save the bees from collapsing on the spot. PvR Do you happen to have a reference for this? The alleged toxicity of Tilia tomentosa is in Bean, Hillier and Elwes & Henry (though Bean sounds a little skeptical - "more research needed"), and scattered across scores of web pages, but I didn't find any web pages on the debunking of this. For example, a web page at the Department of Entomology, University of Michigan. URL:http://www.ent.msu.edu/abj/Article%20pages/jul93.html says "Sometimes, some of the European species are toxic to bees. The greatest offenders are T. tomentosa Moench. and one of its varieties, 'Petiolaris'. Crane et al. (1984) also list T. cordata and the honeydew of T. platyphyllos as at times also being toxic. Muir (1984) adds T. heterophylla Venten. (an American species) and T. x orbicularis to this list. Serious bee poisoning incidents appear to be associated with dry years when the dead and dying bees can be found under the trees. Bumble bees are much more affected than are honey bees that often appear to be totally unaffected during these incidents. The toxicant is thought to be a sugar that is unsuited to the bee's metabolism. Why a species should evolve to poison its pollinators remains a mystery to me." Elsewhere the alleged poison - mannose -is specified, and a hypothesis as to the evolutionary advantage of toxic nectar advanced - deteral of nectar predators, analogous to the toxicity of some bird-distributed fruits to mammals. Limes flower from June to August, which I wouldn't have thought was late in the season (T. tomentosa is the latest flowering of the commonly planted species, so that at least is consistent with the starvation hypothesis). (For example, Sedum is often covered in bees - and butterflies - in September.) -- Stewart Robert Hinsley |
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