USDA. National Agricultural Statistics Service.
In 2016 NASS began to collect data on honey bee health and pollination costs. Provides reliable, up-to-date statistics help track honey bee mortality.
HathiTrust Digital Library.
Thompson, D. Q. (1987). Spread, impact, and control of purple loosestrife (Lythrum salicaria) in North American wetlands. Washington, DC: U.S. Dept. of the Interior, Fish and Wildlife Service.