There have been reports recently of the western corn rootworm becoming resistant to the genetically modified crops designed to protect against them.
It was first discovered by researchers at Iowa State University in 2011, since then pesticide sales risen as farmers turn to chemicals to help protect their crops.
The genetically modified corn, called BT, is still effective against pests that target corn stalks but the toxin the gene creates occurs in smaller amounts in the roots, making them more vulnerable.
Also the lower effectiveness helps encourage resistance compared to the higher rate of the toxin in the stalk.
It also means that even if the rootworms are not resistant, there will still be some present in the field, so how does a farmer know if the bugs in his or her fields have developed this resistance?
Angie Peltier, an Ag educator with University of Illinois Extension office in in Monmouth, said they have to carefully gauge the amount of damage in the field.
"Is it a level of damage that we would expect with this moderate or low dose of the BT protein in the root tissue or is it more than that?" Peltier said.
She said farmers can get a free analysis of the level of rootworm in their fields from U of I Extension at their field day on July 17th.
Peltier said farmers can help combat rootworm resistance by rotating between corn and other crops, and also by varying the specific type of BT they plant, which can contain different forms of the toxin.