Some species of Linden/Basswood (Tilia) are toxic to bees (esp. bumblebees)?! Is this news...

...only to me? I've never seen it mentioned in PC books.

I've been looking at planting some lindens (Tilia sp.) in my yard. Came across some info that the tree can be toxic to bees and dismissed it out of hand. However, in doing further research, it does appear that SOME species of Tilia (called linden/basswood/lime, depending on where you are from) ARE toxic to bees, although it appears the risk is more to bumblebees than honey bees. I am posting some of what I found below. You can follow the links for the full article.

BuzzAboutBees - Which Lime Trees Are Toxic to Bees http://www.buzzaboutbees.net/Which-Lime-Trees-Are-Toxic-For-Bees.html

This article states the T. cordata and T. platyphyllos are fine (non-toxic), but that several others are to be avoided, as they are toxic to bees (it explains why in the article):

Tilia Petiolaris , as are Tilia orbicularis.
Tilia oliveri (Chinese Lime) is toxic for bees.
Tilia tomentosa, (silver lime in the UK and silver linden in the US) – especially toxic for bumblebees, but apparently not so toxic for honeybees
Tilia euchlora
Tilia dasystila

PlanBeeCentral - The Bee Tree article (ironically enough, they are calling the linden tree "the bee tree" - it's not until post #8 that someone points out that some species are TOXIC). http://planbeecentral.wordpress.com/2008/05/12/plant-a-bee-tree/

Does anyone know any more about this?

I don't know about toxicity (can't read the article at the moment) but here our main nectar flow is from the limes an the bees go nuts for it. When the trees are in flower they roar with the sound of bees, the hives are really strong and they honey lovely.

Also,

There are many many possible reason to find dead bees under a tree. When the nectar flow is on strong pretty much all the foragers from a considerable area will hit a very small number of trees. Lets say you have 10,000 bees foraging from a large lime tree or a clump of them. Foragers live a month or so in full summer, so in a given day you would expect 300 or so of those bees to die. If half of them die while at the tree foraging that would lead to a large number of dead bees at the base of the tree over a period of just a few days.

Not the trees fault, just a fact of the bees being concentrated in one place due to the extreem nectar flow.

In addition, other external factors can contribute to bee death - flying past crop spraying on the way to the trees for example.

If lime nectar really were toxic I'd expect to see the effects acting on the rest of the colony back in the hive, not just the foragers. If colonies were suffering due to this nectar source you can be pretty sure that beekeepers over the past few thousand years would have noticed!

Hmmmm, if you read the articles, you'll see there is evidence that toxicity exists.

And the reasons the beekeepers over "thousands of years" haven't noticed is because the toxicity that does exists is largely due to non-native linden trees now being planted in areas where that particular species has never been available to bees before. The bees do like the trees and do visit them and there are several lindens that are wonderful for bees...however, the problem is with some of the non-native species that they (bumblebees in particular) can't ingest the nectar (going of memory here).

I appreciate you taking the time to reply. However, you also stated that you didn't read the articles, so it feels like you are reacting more than giving an opinion based upon research.

I think I need perhaps to seek out an entymologist. Will post again if I find out more.

Has anyone found anything more about this? I've been planting littleleaf linden (Latin name "cordata") for bees, both native and otherwise. I've heard they're ok and that's what the poster's article indicates but I've heard of a few times that dead bumblebees were found beneath littleleaf lindens in bloom

Here is an excellent in depth article on this topic, that disputes that linden trees are inherently toxic. However, it appears that they can cause starvation in bees especially if alternative food sources are unavailable since they stop producing nectar late in their bloom cycle, but continue to attract bees: https://royalsocietypublishing.org/doi/10.1098/rsbl.2017.0484