CHAMPAIGN, Ill. – More than 90 percent of Illinois corn producers polled at the University of Illinois Extension Corn and Soybean Classic meetings indicated that they planned to plant corn that was genetically modified with the insect-killing protein Bacillus thuringiensis this spring.
Commercially available since 1996, Bt corn is resistant to European corn borers, western corn rootworm and other crop-destroying insects. | Photo by L. Brian Stauffer
However, significantly fewer – just 75-80 percent – of them said that they also planned to comply with the U.S. Environmental Protection Agency’s requirement that they plant 20 percent of their corn acreage with non-Bt seed. The non-Bt seed creates refuges that prevent or delay the development of genetic resistance among insects by ensuring that an ample supply remains susceptible to the Bt toxin, a naturally occurring soil bacterium, and pass that susceptibility on to their offspring.
Another 5-10 percent of the growers indicated that they would not plant any refuge acres.
Producers’ growing noncompliance with the refuge requirement is cause for concern because it could, at some point, hasten the onset of genetic resistance, leading to a resurgence of European corn borers, western corn rootworms and other crop-destroying insects that Bt has been keeping at bay, according to Michael E. Gray, a professor of agricultural entomology in the department of crop sciences and assistant dean in the College of Agricultural, Consumer and Environmental Sciences at Illinois.
Gray, who conducted the poll, is one of several U. of I. scientists involved in the annual Corn and Soybean Classic meetings, which are held at six sites throughout Illinois and explore crop production and insect management techniques.
The percentage of noncompliant growers at the January meetings was consistent with data reported by the national watchdog group Center for Science in the Public Interest, which indicated that while only 10 percent of U.S. corn producers were noncompliant from 2003-2005, by 2008 the number of growers disregarding the EPA’s refuge requirement swelled to 25 percent.
The evolution of genetic resistance in insects is probably “inevitable” and can develop within 15-25 years, Gray said. Bt corn has been commercially available since 1996.
“Considering this technology has been in the market place for 15 growing seasons and remains the predominant corn insect management strategy in the north central region of the U.S., perhaps we should be surprised that resistance has not yet occurred,” Gray wrote in a recent article. “As the widespread use of Bt corn continues and the duration of exposure (many growing seasons) to corn insects increases, the potential development of resistance becomes magnified. This accentuates the importance of refuge compliance by corn producers.”
The Center for Science in the Public Interest is urging EPA officials to crack down on noncompliance by requiring seed companies to conduct regular field inspections, to restrict or deny seed corn sales in geographic areas where noncompliance rates remain high, and to require that farmers provide purchase records and maps of their Bt and non-Bt crops.
Growers can plant refuges of non-Bt corn as strips of four to six rows within their fields or as blocks near their Bt corn. To simplify refuge management and increase compliance, the seed industry may shift to seed mixtures called “refuge in a bag” that intersperse non-Bt seed with Bt seed in every bag, thus throughout the fields, Gray said. The first commercial product, Pioneer HiBred’s Optimum® AcreMax™, available to growers this year, contains 90 percent Bt seed and 10 percent refuge seed.
However, the hybrid blend may be less effective at managing insects, with resistance anticipated to occur in a little more than 11 years, according to an EPA analysis.
A 95 percent Bt/5 percent refuge seed hybrid mixture called SmartStax™, which expresses several proteins – one toxin that controls corn rootworms, a second that targets lepidopteran pests and one for herbicide tolerance to two active ingredients – will become commercially available on a broad scale in 2012. According to the EPA’s estimate, the product is 150 percent as durable as a single-toxin hybrid and structured refuge in terms of delaying resistance.
About 80 percent of growers polled at the Corn and Soybeans Classic meetings indicated they would be willing to plant a seed blend that contained 2-5 percent non-Bt seed; however, if the blend of non-Bt seed were increased to 6-10 percent, the proportion of growers willing to use it dropped to 53 percent.
But even corn producers who don’t plant Bt hybrids benefit from the areawide pest suppression generated by neighboring fields, Gray said. “And the producers who plant nontransgenic corn actually benefit more than those who grow Bt corn because they pay less for their non-Bt hybrid seed.”
Bt hybrids generated cumulative benefits of $3.2 billion – including higher yields and reduced costs for pesticides – for corn growers in Illinois, Minnesota and Wisconsin during the products’ first 14 years on the market, according to a paper published in Science last October of which Gray was a co-author. Even producers in Illinois, Minnesota and Wisconsin who elected not to grow Bt hybrids reaped $2.4 billion in benefits.
The western corn rootworm, dubbed the billion-dollar insect in reference to its costs in crop damage and insecticide usage, has been diminished by the widespread planting of Bt crops, intense use of broadcast applications of fungicides and insecticides in corn and soybean fields, and consecutive wet springs during late May and early June when larvae were hatching.
Densities of European corn borers began decreasing dramatically when Bt corn’s popularity began to surge in 2005-2006 and have been at historic low levels the past few years, Gray said.
“There’s been this very significant areawide, regionalwide suppression of the European corn borer. Bt hybrids have lowered this once very prominent insect pest to almost non-pest status.”
Motorists in the Corn Belt may recall past summers when they drove in rural areas after nightfall and their windshields were bombarded continuously with swarms of large insects.
“People often ask me, ‘What happened to all those bugs we used to have?’ ” Gray said. “I tell them, ‘Bt corn.’ ”