Insects, such as honey bees, are the world's most important pollinator of food crops. It's estimated that at least one-third of food consumed by humans relies on pollination mainly by bees, but also by other insects, birds, and bats.
Neonicotinoid usage has been linked to honey-bee colony collapse disorder and loss of birds due to a decline in insect populations.
Klein said neonicotinoid became popular with farmers during the mid-2000s, has contributed to the dramatic increase of toxic farmland.
The study found imidacloprid and clothianidin, produced by Bayer, and thiamethoxam, a product of Syngenta-ChemChina were the three neonicotinoids that contributed to the increasing toxic load in farmlands.
Last year, Europe banned three main neonicotinoids (clothianidin, imidacloprid, and thiamethoxam) for all farming activity. Several states in the US have also restricted farmers from using the chemicals, out of fear that it could further collapse the honey bee population.