What are environmental concerns of genetically engineered crops?

Once an area loses biodiversity there are increased risks of damaging the surrounding environment and of a shortage. Insects that once feasted on different kinds of crops leave the area, the animals that eat those insects leave the area, and pests can move in that have built up a resistance to the genetic toxin. If the genetically engineered crops fall victim to some new disease or pest, then the entire crop may be lost as opposed to only one kind.

Scholars who have done a study on this could explain it better. See below under Related links.