https://en.wikipedia.org/wiki/List_of_crop_plants_pollinated_by_bees
https://www.nrdc.org/onearth/would-world-without-bees-be-world-without-us
https://entomology.ca.uky.edu/ef608
http://msutoday.msu.edu/news/2015/wild-bee-decline-threatens-us-crop-production/
https://www.usda.gov/nass/PUBS/TODAYRPT/hcny0516.pdf
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2606032/