Exposure to corn pollen containing genes for "Bacillus thuringiensis" (Bt) production may weaken the bees' defense against "Nosema". In relation to feeding a group of bees with Bt corn pollen and a control group with non-Bt corn pollen: "in the first year, the bee colonies happened to be infested with parasites (microsporidia). This infestation led to a reduction in the number of bees and subsequently to reduced broods in the Bt-fed colonies, as well as in the colonies fed on Bt toxin-free pollen. The trial was then discontinued at an early stage. This effect was significantly more marked in the Bt-fed colonies. (The significant differences indicate an interaction of toxin and pathogen on the epithelial cells of the honeybee intestine. The underlying mechanism which causes this effect is unknown.)"