The Research - Part 1

Historically farmers have controlled CRW two ways:  1.)  by planting a crop other than corn every other year (crop rotation) or 2.) with soil insecticides when corn is grown year after year (continuous corn) since CRW causes the most damage to corn roots during the larval stage.  Over the years, CRW populations have evolved resistance to some of these insecticides.  Dr. Siegfried’s research investigates CRW populations at the molecular level to determine if insecticide resistance is present in these insects. 

Researchers like Drs. Siegfried and Meinke are motivated to continue conducting research on CRW because of the potential benefit for farmers.  Damage to the plant roots has negative impacts on the rest of the plant.  If the roots are severely damaged the plant cannot effectively take up water and nutrients, in addition the plant will be less structurally stable.  These factors can negatively affect plant growth and lead to yield loss.  Therefore farmers are highly motivated to control CRW in the larval stage of development to increase their yield at harvest. 

Figure 3: CRW larvae. (Richard C. Edwards, Purdue,

With the development of rootworm Bt (Bacillus thuringiensis) corn, CRW control transitioned to using fewer soil insecticides and instead began relying upon proteins in Bt corn to prevent CRW damage.  In the same way that Bt corn changed how farmers controlled European corn borer, it changed the options farmers had to control CRW (for more information about the different kinds of Bt, see The New Bts and the PDF Handy Bt Trait Table.  The Bt proteins used in rootworm Bt corn are different than the Bt proteins in Bt corn used to control European corn borer.  This is because European corn borer is classified as lepidopteran (moth or butterfly) and corn rootworm is classified as coleopteran (beetle).  These two Bt's have even been combined into one corn hybrid to provide both above-ground control against European corn borer and below-ground control against CRW in one plant.     

Farmers no longer have to only rely upon insecticides (synthetic neurotoxins) to prevent damage to their cornfields because Bt corn provides a more selective (highly specific to CRW) management option.  Besides being more selective compared to traditional insecticides, by planting rootworm Bt corn farmers ensure every plant with the Bt protein is protected from CRW.  On the other hand, soil insecticide effectiveness is dependent on application timing and placement of the insecticide so CRW come in contact with it, and on environmental factors that can negatively affect the consistency of the soil insecticide. With Bt corn, crop management is simplified and there are fewer health risks to applicators since the insect protection for the whole season is already contained within the corn seed at planting.  For farmers these are major advantages and, therefore, an increasing number of corn acres in the United States are currently planted to Bt corn.  Since Bt corn potentially provides such great protection against CRW, is there any disadvantage to planting so many acres of Bt corn? 

In the short-term Bt corn has been very effective at controlling the CRW populations in cornfields.  However, the long-term use of Bt is a little less certain since some control failures have recently been reported.  Anytime a control method is used exclusively over a period of time there is a high likelihood that the pest population will evolve resistance to that control method.  The research done by Dr. Meinke and Dr. Siegfried allows them to gather information about CRW populations to optimize resistance management strategies and to help predict how quickly CRW may evolve resistance to specific control methods such as Bt corn.