Risks:

Though bacillus thuringiensis has been shone to hold no signifcant harm against humans, some strains have been known to produce food poisoning and light stomach aches. Still, these conditions are temporary, and thought to be not too offensive compared to the damage b.t. can accomplish against insects.

Also, with using any pesticide or bacteria for long and large amounts, resistance may appear. There is no exception for bacillus thuringiensis. Used more and more as a crop in recent times, insect resistance may develop faster and better. As the crop is used, small colonies of bugs may hold genetic alterations that allow it to live through the pesticide's effects. Over time, these insects will probably reproduce and pass along these genetics to offspring, allowing for a whole population of insects to become specifically resistant.

This means, that gradually b.t. will no longer be able to kill insect populations, and other means and pesticides will have to be discovered.