Not concerned about genetically engineered foods and crops? You should be!! Here is a report about the weeds and insects which have developed resistance to what is supposed to kill them.
1. Nature cannot stand a monoculture. And that's usually how crops are planted nowadays for ease of mechanized farming.
2. If you mess with Mother Nature, she will find a way to strike back. It's really not surprising that some plants and insects might be resistant to herbicides and insecticides.
In case you need proof, here it is: