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

Stewart Robert Hinsley schreef
Do you happen to have a reference for this?

+ + +
Not so as to be immediately useful
1) I read about it in a Dutch magazine (Natura)
2) It was about ten years back, give or take a few years, not sure exactly
when
3) I cancelled my membership several years back and I don't even remember if
I kept my magazines, let alone where they went.

However they were very keen on this sort of thing and not likely to publish
something not carefully looked at. The article, as I remembered, dealt with
Tilia in general.
PvR

Tilia americana is known as a source of large quantities of high-quality honey.
Honey bees are not badly affected by the tree, but their behavior is difficult
during a basswood honey flow -- the tree makes nectar for only a few hours a
day, and for the remainder of the day, the bees tend to be unpleasant to work
with. But I've never heard that it was due to any sort of toxicity; rather,
honey bees always become testy when a source of nectar suddenly dries up. In
any case, the colonies remain healthy.