I'm not in the US but this seems to be the biggest study there http://www.sciencemag.org/content/339/6127/1611 http://www.sciencemag.org/content/339/6127/1611

I'm not in the US but this seems to be the biggest study there http://www.sciencemag.org/content/339/6127/1611 http://www.sciencemag.org/content/339/6127/1611 >Using historic data sets, we quantified the degree to which global change over 120 years disrupted plant-pollinator interactions in a temperate forest understory community in Illinois, USA. We found degradation of interaction network structure and function and extirpation of 50% of bee species. Network changes can be attributed to shifts in forb and bee phenologies resulting in temporal mismatches, nonrandom species extinctions, and loss of spatial co-occurrences between extant species in modified landscapes. Quantity and quality of pollination services have declined through time. The historic network showed flexibility in response to disturbance; however, our data suggest that networks will be less resilient to future changes. News article: http://www.theguardian.com/environment/2013/feb/28/wild-bees-pollinators-crop-yields http://www.theguardian.com/environment/2013/feb/28/wild-bees... Pesticides are far from the only factor, but adding that to habitat loss and climate change is hardly helping.