New research on bumble bees uncovers some interesting facts. Apparently, despite being hired to pollinate crops, bumble bees go elsewhere on a regular basis. The rascals! However, they need to do this, because monocultures are not nutritiously varied enough.

> Recent studies from North America suggest that disease transmission from commercially reared bumble bees to wild populations has led to marked range contractions in some species. ... We determined the permeability of cropping systems to commercial bumble bees, and quantified the prevalence of four pathogens in commercial Bombus terrestris hives and adjacent conspecific populations at increasing distances from greenhouses in Ireland. 

> Commercial bumble bees collected from 31% to 97% of non-crop pollen, depending on the cropping system, and hives had markedly higher frequencies of two gut parasites, Crithidia spp. and Nosema bombi, compared to adjacent populations, but were free of tracheal mites. The highest prevalence of Crithida was observed within 2 km of greenhouses 

-- Tomás E. Murray, et al (2013) 
Pathogen prevalence in commercially reared bumble bees and evidence of spillover in conspecific populations
Biological Conservation 159  269–276

* * *

Bumblebee communities and their foraging resources were surveyed in south Swedish agricultural landscapes
of contrasting complexity, defined by the size of arable fields and the amount of permanent grazed
pastures. 

The seasonal pattern of bumblebee abundance differed between landscape types. Initial bumblebee abundances
were equal in both landscape types. However, by late July there was a sharp decline of bumblebees in
simple landscapes, while the abundance continued to increase in complex landscapes. This suggests that
a larger proportion of bumblebee colonies may fail to reproduce in simple landscapes despite a beneficial
early season. 

Overall, bumblebee abundance in late July was positively related to three inter-related
variables: area of permanent pasture, area of ley fields and total amount of herbaceous flowers, while
early abundances (June to early July) did not relate to these variables. We suggest that in simplified landscapes
of this region, bumblebee abundance is limited by floral resources mainly from midsummer and onward.  

-- Anna S. Perssona, Henrik G. Smith. (2013). 
Seasonal persistence of bumblebee populations is affected by landscape context. 
Agriculture, Ecosystems and Environment 165  201–209

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