Does feeding location on roots influences the western corn rootworm development?

Western corn rootworm (Diabrotica virgifera virgifera LeConte) is the main corn pest in the U.S. Controlling this pest has been a major challenge. In 2003, genetically modified corn producing Cry proteins targeting the larval stage of western corn rootworms was released, and this has led to a substantial reduction in insecticide use in North America. Therefore, limiting the likelihood of resistance in western corn rootworm population has been a main concern.

It has been observed that the concentration of Cry toxin expressed by Bt corn hybrids is most effective against the first instars of western corn rootworm. It is also known that first instar larvae feed on the tip of the roots while later instars have a tendency to feed closer to the basal part of the root. Therefore, we wish to test the hypothesis that the part of the root on which larvae feed influences their survival.

We designed a system to control larval access to different areas of the root. We used pots in which we planted Bt corn hybrids targeting western corn rootworm and a non-Bt hybrid. We separated the base from the top of the roots by introducing a layer of expanding insulation foam that limited the potential of the larvae to move up or down. Then, we introduced the eggs in the upper part or lower part and compared the size, weight and survivorship of larvae in the two treatments.