>Out of 25 bumblebee species in the UK, for example, two have gone extinct and eight decreased substantially in abundance since 1940...

I thought that we were talking about honey bees.  Yes, we certainly saw a huge reduction in the numbers of bumblebees in this area during the latter part of the 20th century - mainly through the aerial, then ground spraying of Hostathion on rape I suspect (now illegal of course).  In other areas loss of habitat has been blamed and recently we have learned that bumblebees (and solitary bees) are definitely affected by neonicotinoids.

Having said that, we now seem to have very large numbers of bumblebees, one species thought to be extinct has re-appeared (Bombus ruderatus from memory) and we have gained a species from the continent - Bombus hypnorum.

>In England for example, the importation licences for the non-native subspecies most commonly imported are specifically limited to parasite-free colonies, and 40–50 thousand colonies are imported annually to the UK on this basis (Natural England 2009, 2012). 

This is a major concern, with the Anatolian sub-species now threatening our native Bombus terrestris.  Although these colonies are required to be destroyed after their pollination work is finished, they are often used in open ended polytunnels allowing escape into the wild.

Best wishes

Peter 
52°14'44.44"N, 1°50'35"W

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