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Funded Project

Funding Program: Regional IPM Competitive Grants - Northeastern

Project Title: Evaluation of Non-corn Plants as Refugia in a Resistance Management Program for ECB on Bt-corn

Project Director (PD): John Losey [1]

Lead State: NY Lead Organization: Cornell University

Research Funding: $92,102

Start Date: Sep-01-1998 End Date: Aug-31-2000

Site/Commodity: field corn

Area of Emphasis: plant resistance, biological control, biocontrol

Summary: The European corn borer (ECB), Ostrinia nubilalis (Hubner), is a major pest of field corn in the northeastern United States. Although a combination of control methods have been used over the last forty years to reduce ECB population levels, ECB continues to cause substantial yield losses each year. A new technology in which a gene from a bacterium, Bacillus thuringiensis (Bt), is spliced into the DNA of corn plants is now available that can further reduce ECB populations and its effect on corn yield. This technology is an improvement over past control tactics because it integrates the best aspects of biological control and host plant resistance with the effectiveness, efficiency, and reliability of an insecticide based program. Furthermore, Bt-corn hybrids provide season-long protection against corn injury by ECB which insecticide programs cannot economically provide. The commercial availability of Bt-corn has the potential to provide for the first time an economically-viable strategy for managing ECB in the Northeast. Among the positive attributes of Bt-corn hybrids are high selectivity, ease of use, and negligible risk of environmental contamination. The Bt toxin is selective for ECB and is non-toxin to humans, livestock, and wildlife. However, there are two potential problems with the widespread adoption of Bt-corn hybrids, the development of resistant ECB populations and the possible elimination of hosts for several important ECB parasitoids. The potential development of Bt resistant populations has lead the U.S. Environmental Protection Agency to require a resistance management program as part of the product's registration. To meet this requirement, researchers and industry representative have met to develop a consensus on how a resistance management program should be implemented. The theory behind a resistance management program is to set aside a certain percentage of crop acreage as "refugia" where ECB are not exposed to the Bt toxin to ensure a pool of susceptible individuals that can mate with any resistant survivors to delay or prevent the development of resistance. The recommendation for refugia developed as a consensus by the University-Industry Task Force was for farmers to set aside 20 to 30% of corn acreage. The tactical implementation of this refugia, however, was not well defined because many important aspects of ECB biology and behavior are not understood. One issue is the importance of non-corn hosts as refugia for susceptible ECB. ECB has a host range of over 200 plants and these plants could act as untreated refugia. The relative abundance of these non-corn host plants varies widely between regions in the U.S. Hence, a resistance management program developed for the Midwest, with a predominance of corn and soybeans as a ground cover, may not be appropriate for the Northeast region because of the much high vegetational diversity. Specifically, refuge requirements designed for the Midwest may be unduly large and costly for farmers in the Northeast if adequate refugia exists outside their corn fields. Unfortunately, little is known about the suitability of non-corn plants as hosts for ECB. This lack of knowledge has prevented researchers from factoring the value of non-corn refugia in to the design of a resistance management program. To address this knowledge gap we propose research that will 1) determine the proportion of ECB adults that develop on plants other than corn, 2) determine the probability that ECB that develop on corn will mate with ECB that develop on other plants, and 3) determine the importance of non-corn plants as sources of ECB hosts for parasitoids. Once this information is available we will be able to develop a program for the long-term sustainable use of this new technology which is specifically tailored to agroecological conditions in the Northeast. Objectives: Our first three objectives focus on determining the importance of non-corn plants as refugia for susceptible ECB and our final objective focuses on determining the suitability of these same plants as sources of ECB hosts for parasitoids. Objective 1: Assess ECB densities in field corn and non-corn hosts within the crop landscape. Objective 2: Compare ECB larval developmental rates on field corn and select non-corn hosts. Objective 3: Determine the sex pheromone affinities of adult ECB reared from field corn and non-corn hosts. Objective 4: Compare ECB parasitism rates for larvae feeding on field corn and select non-corn hosts. Outcomes and Impacts Summary from 2001 IPM Center report The European corn borer (ECB) has been a major pest of field corn in the Northeast, causing annual losses of about $24 million. Scientists have used biotechnology to produce a new type of corn, known as Bt-corn, that reduces ECB populations and their damage. There is concern, however, that widespread use of Bt-corn hybrids might lead to the development of ECB populations that are resistant to the Bt toxin. This resistance could devastate not only the corn industry but also other crops that are prone to ECB damage, such as potatoes, peppers, and even apple trees. Growers use resistance management programs to prevent or delay the development of resistance, planting non-Bt-corn on some of their acreage to provide a refuge where ECB are not exposed to Bt. This practice ensures that a pool of susceptible corn borers remains to mate with insects that have greater resistance, and thus maintains susceptibility in the species as a whole. John Losey examined the ability of plants other than corn to act as a refuge for a portion of the ECB population. Typically, growers must set aside as much as 20 to 30 percent of their corn acreage as refuge, but experts were uncertain whether it was necessary to establish such a large corn refuge area. Losey found that non-corn species did not provide an adequate supply of susceptible ECB to prevent or slow resistance. His finding suggests that growers should maintain their on-farm refuges of non-Bt-corn in order to promote the long-term, sustainable use of Bt-hybrid corn as a powerful control tool.

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