Pesticides work in two ways to reduce bee populations.
First, many pesticides necessary in crop production are highly toxic to honey bees. Second, the use of herbicides reduces the acreages of attractive plants for the bees to forage on. Pesticide damage to colonies takes many forms. Bees may be poisoned when they feed on nectar or pollen contaminated with certain pesticides. Bees may also be poisoned when they fly through a cloud of pesticide dust or spray or walk on treated parts of a plant.