Bt Stacks, Seed Treatments, and Soil Insecticides: Optimizing IPM and IRM for Corn Rootworms
Professor & Interim Assistant Dean, ANR Extension
N-305 Turner Hall
The history of western corn rootworms and the evolution of control tactics targeted at this impressive insect pest provide a remarkable and intriguing case study of management successes and failures. An abbreviated timeline of significant western corn rootworms events reads as follows.
- Historical origins – western corn rootworms have been inhabitants of corn in Central America for roughly 5,000 years
- Occupied the western-half of the Great Plains of the US since at least 1867
- Originally called the Colorado corn rootworm
- 1929 and 1930 – root injury in cornfields of southwestern Nebraska attributed to western corn rootworms
- 1940s and 1950s – western corn rootworms disperse across Nebraska
- 1959 – control failures reported with soil insecticides targeted against corn rootworms in some areas of Nebraska
- 1962 – western corn rootworms in Nebraska reported to have resistance to the chlorinated hydrocarbon insecticides aldrin and heptachlor
- 1964 – western corn rootworms enter northwestern Illinois
- 1981 – enhanced microbial degradation of carbofuran in soils confirmed
- Mid-1980s – western corn rootworms found in western Virginia
- 1987 – root injury to first-year corn caused by western corn rootworms reported in Ford County, Illinois
- 1992 – western corn rootworms discovered in Europe, in cornfield near Belgrade airport
- 1995 – widespread damage by western corn rootworms occurs in first-year corn (corn following soybean) across east central Illinois and eastern Indiana
- 1998 – western corn rootworm resistance to an organophosphate (methyl parathion) and a carbamate insecticide (carbaryl) reported in Nebraska due to broadcast applications of these products to control adults and suppress egg laying
- 2003 – Bt corn hybrids for corn rootworm control enter the market place
- 2005 – researchers conclude in Science that multiple transatlantic introductions of western corn rootworms into Europe have taken place
- 2007 – western corn rootworms found in 20 European countries
- 2010 – anticipated commercialization of SmartStax™ hybrids for control of multiple insect pests of corn, including corn rootworms
The use of “stacked” Bt hybrids by Illinois producers is expected to increase. In 2007 and 2008, 40% and 52%, respectively, of all corn planted in Illinois was a stacked Bt hybrid (USDA ERS) (Figure 1). In 2010, Monsanto Company and Dow AgroSciences LLC via a cross licensing agreement are anticipated to begin the commercialization of SmartStax™ corn hybrids that express simultaneously several Cry proteins (Cry3Bb1, Cry1A.105+ Cry2Ab2, Cry34/35Ab1, Cry1F) targeted against lepidopterans and corn rootworms. In addition, these hybrids will provide herbicide tolerance to two herbicides (glyphosate and glufosinate).
In 2008, we conducted experiments with the SmartStax™ technology in plots established at the University of Illinois near the Urbana campus. The trials were sponsored by the Monsanto Company. The level of root protection afforded by the SmartStax™ treatment was exceptional in early (Figure 2) and late August (Figure 3) despite significant pressure (over two nodes of roots destroyed) in the control treatment.
Many questions linger regarding IPM and IRM issues with respect to western corn rootworms, such as: 1) Will the “stacking” or “pyramiding” of genes, required for the expression of multiple Cry proteins, sustain the durability of Bt hybrids well into the future? 2) By increasing the use of stacked Bt hybrids that express several Cry proteins (targeted against corn rootworms) within a single plant, can producers delay the onset of resistance while also reducing the refuge spatial requirements? 3) As with other insecticides, will resistance develop within western corn rootworm populations to the neonicotinoid seed treatments used on Bt seed? and, 4) What does the future hold for granular formulations of soil insecticides? A quick review of the history of western corn rootworms should teach all of us an important lesson – more management challenges will emerge.