In what may be one of the most "real world" studies yet on the impacts of sub-lethal doses of pesticides upon honeybee colonies, researchers collected pollen samples from the field and analyzed them for pesticide loads.
"Pesticide exposure and pathogens may interact to have strong negative effects on managed honey bee colonies. Such findings are of great concern given the large numbers and high levels of pesticides found in honey bee colonies. Thus it is crucial to determine how field-relevant combinations and loads of pesticides affect bee health. We collected pollen from bee hives in seven major crops to determine 1) what types of pesticides bees are exposed to when rented for pollination of various crops and 2) how field-relevant pesticide blends affect bees’ susceptibility to the gut parasite Nosema ceranae."
"We detected 35 different pesticides in the sampled pollen, and found high fungicide loads. The insecticides esfenvalerate and phosmet were at a concentration higher than their median lethal dose in at least one pollen sample. While fungicides are typically seen as fairly safe for honey bees, we found an increased probability of Nosema infection in bees that consumed pollen with a higher fungicide load."
"While multiple studies have shown negative effects of specific pesticides on honey bee individual and colony health , , ,  and high pesticide exposure , , ours is the first to demonstrate how real world pollen-pesticide blends affect honey bee health."
"Insecticides and fungicides can alter insect and spider enzyme activity, development, oviposition behavior, offspring sex ratios, mobility, navigation and orientation, feeding behavior, learning and immune function , , , –. Reduced immune functioning is of particular interest because of recent disease-related declines of bees including honey bees , . Pesticide and toxin exposure increases susceptibility to and mortality from diseases including the gut parasite Nosema spp. , . These increases may be linked to insecticide-induced alterations to immune system pathways, which have been found for several insects, including honey bees , –."