Objective 3. Evaluate the role of natural enemies of lepidopteran
pests in corn cropping systems and agricultural landscapes
Michigan (lead), Minnesota, and Ohio will conduct surveys in landscapes where European corn borers have historically been pests or not, and Iowa, Minnesota, South Dakota, Missouri, and Texas will conduct natural enemy surveys associated with Bt corn and non-Bt corn prior to and after the widespread adoption of Bt corn. All sites will map the cropping systems and land use patterns in a 1-mi radius surrounding the surveyed target fields, and will count natural enemies on at least 100 randomly selected corn plants at 2-week intervals beginning in early to mid-June through August. To provide more detailed patterns of abundance and diversity, Michigan and Minnesota will conduct more intensive sampling, as often as twice a week. Michigan, Minnesota, Iowa, and Texas also will collect at least 100 corn borer larvae during the first and second generation and evaluate parasitism rates by specialized insect parasitoids, focusing on Macrocentrus grandii, Eriborus terebrans, and several tachinid species.
Iowa is coordinating research (with Delaware, Indiana, Kansas, Kentucky, Maryland, Minnesota, Nebraska, New York, Ohio, Pennsylvania) to evaluate the potential effect of Bt corn on the specialized pathogens attacking European corn borer. Participants will collect five cornstalks from a Bt- and non-Bt cornfield, and will collect at least 25 European corn borer larvae from the non-Bt cornfield. Larvae will be evaluated for infection by Nosema pyrausta, a microsporidian pathogen, and Beauvaria bassiana, a fungal pathogen, and cornstalks will be evaluated for the presence or absence of endophytic B. bassiana. Texas will conduct more extensive studies on southwestern corn borer, with sentinel egg masses, larvae, and pupae to estimate mortality rates on these stages. Michigan and Minnesota also will sample some of the surrounding habitats and noncorn crops to evaluate how the natural enemy communities use the entire landscape. Minnesota will focus on how the predator complex uses small grain crops, especially wheat and barley. These natural enemies will be sampled with beat samples to characterize colonization, emigration, and reproductive response of coccinellids and anthocorids in the small grains. Michigan will experimentally manipulate landscapes by selective addition of landscape elements, such as floral or microhabitat diversity, and measure movement of natural enemies.
Minnesota will conduct experiments to determine if natural enemies of larval European corn borers have the potential to delay or accelerate resistance evolution (Gould et al. 1991). Outbreaks of resistant larvae in a Bt cornfield will be simulated by planting non-Bt plants in small patches and inoculating these plants with European corn borer. Approximately 5,000 female M. grandii will be released in these fields to determine if they key into these incipient outbreaks or avoid them. In addition, by using European corn borer larvae with genetic differences in developmental rate, these experiments will test whether the predicted developmental delay in resistant insects will result in higher mortality from natural enemies.
New York and Iowa will evaluate early-season inoculative releases of Trichogramma ostriniae in several regions with differing environments and European corn borer pressures. They will improve release and rearing techniques for T. ostriniae by determining 1) dispersal rates of T. ostriniae to optimize number of release points per acre, 2) influence of food resource availability (nectar and aphid honeydew) on effectiveness of T. ostriniae, 3) optimal cold-storage and diapause-induction conditions in T. ostriniae for optimal production system and reduced costs, and 4) compatibility of T. ostriniae releases with current insecticides. Inoculative releases of T. ostriniae will be made in early-season fields of fresh market sweet corn and European corn borer egg parasitism measured with naturally laid and sentinel egg masses. Crop quality will be compared in release and nonrelease fields (Prokrym et al. 1992). To determine the number of release points per acre, wasp dispersal will be measured by monitoring rate of movement away from single release points.
Illinois will continue efforts to evaluate known natural enemies of other stalk-boring pests for their potential use against European corn borer and southwestern corn borer. Work will evaluate ecological and physiological compatibility of exotic parasitoids from other stalk-boring insects (e.g., T. ostriniae from Ostrinia furnacalis, several Cotesia spp. from Old World Chilo spp.). The specificity of these parasitoids for stalk borers in corn will be evaluated to characterize the potential environmental risks of introducing these species. As they become available, other crambid and pyralid species will be tested as potential hosts, as well as rare and charismatic species of Lepidoptera. Additional species will be assessed as potential candidates for introduction (Wiedenmann and Smith 1997).
Illinois will use regional data collected from previous multistate collaborations and the proposed research to estimate the economic value of natural enemies for several cropping systems by adding natural enemies into an existing simulation model of European corn borer population dynamics. A model for N. pyrausta (Onstad and Maddox 1989) and M. grandii (Onstad and Kornkven 1999) will be used to project the effect of natural enemies on the population dynamics of European corn borer. These effects will be used to project the value of these natural enemies in terms of pest management, yield loss, and economic gain. Specifically, the projected effects of widespread adoption of Bt corn on natural enemies will be modeled to assess the natural enemy cost of Bt corn.
Objective 4. Assess impact of management strategies for
stalk-boring insects on nontarget organisms
Field studies will be conducted to develop management tactics and decision support systems for nontarget pests that survive Bt corn exposure. Maryland, Delaware, Virginia, Illinois, Minnesota, and Wisconsin will conduct replicated plot experiments of multiple treatment regimes initiated at various plant phenology stages to determine the optimal number and timing of insecticide applications required to manage lepidopteran survivors of Bt sweet corn and dusky sap beetle. A census of insect stages infesting the ear will be taken at each plant stage to determine when lepidopteran larvae recover from B. thuringiensis intoxication and enter the ear. Cost-benefit analysis will be conducted to evaluate the economic feasibility of Bt sweet corn under various target and nontarget pest risk scenarios and technology costs. Kansas and Oklahoma will conduct research to evaluate pesticide and nonpesticide options for control of the Banks grass mite in Bt corn.
Several studies are planned to determine the impact of Bt corn on local suppression of European corn borer and other lepidopterans in host plants grown nearby. Pennsylvania and Maryland will determine if Bt sweet corn preferentially attracts European corn borer females relative to peppers and snap beans. The approach will be to release adults reared on colored diet at a central location and allow them to choose among the three host crops and between two growth stages within each crop. The diet will impart a red color to the egg masses, thus allowing for discrimination between eggs laid by released females versus native ones. Relative oviposition rates will be based on the number and ratio of colored and native egg masses on each crop. Studies also will assess the trap-out effect of Bt sweet corn in a diversified crop system and evaluate its feasibility as a farm-scale management strategy. In three states, eight spatially separated blocks will be planted-four with peppers only and four with peppers flanked by Bt sweet corn on both sides. The number and percentage of European corn borer-damaged peppers will be recorded by row to assess gradient effects from the adjoining sweet corn rows. Differences in pepper damage in plots with and without sweet corn will indicate the protective capability of Bt sweet corn. A similar hypothesis will be tested in Maryland, Virginia, and North Carolina where a geostatistical approach of grid sampling infestations of corn earworm will be used to quantify the spatial dependence of corn earworm populations between corn and soybean fields. This study will provide information for landscape modeling to determine if Bt corn indirectly reduces the risks of corn earworm in soybean on a local scale. Expected outcomes of both studies will include recommendations on the amount and spatial arrangement of Bt corn acreage required on farms to achieve localized suppression, thus reducing insecticides beyond the target area.
A project involving New York, Maryland, Iowa, Kansas, Pennsylvania, Wisconsin, Minnesota, and Nebraska will assess various risk factors associated with Bt pollen and its effects on one common nontarget lepidopteran species, the monarch. A comprehensive survey will be conducted in representative sections of each state to characterize the distribution of milkweeds and monarch activity in both agricultural and nonagricultural habitats. Leaves of milkweed plants associated with cornfields at peak anthesis will be sampled, and data on pollen deposition per leaf surface area will be related to distance from corn. Pollen traps also will be used at various points around selected cornfields to monitor pollen deposition over time. Laboratory bioassays will determine the decay rate of the endotoxin in Bt pollen and the survival and fitness of monarch larvae exposed to various Bt pollen concentrations as a standard dose-response relationship.
Choice and no-choice tests in both caged and open-field settings will examine the behavior of monarch larvae and egg-laying females to determine whether the monarch butterfly exhibits avoidance behaviors that reduce the consumption of Bt corn pollen on their host plants. Based on data from Monarch Watch networks at www.MonarchWatch.org/ and agronomic characters of corn hybrids, a corn and monarch phenology model will be developed to estimate the temporal overlap of monarch phenology and corn anthesis in the major corn production areas. Several states also will conduct replicated field tests and laboratory bioassays to compare the risks of Bt pollen drift to nontarget lepidopterans on noncorn hosts to the risks posed by conventional pesticide drift.
Objective 5. Developing and disseminate information for
use by IPM educators, policymakers, and regulators
Minnesota, Iowa, Illinois, Kansas, Maryland, Michigan, and Ohio will conduct field evaluations to determine the efficacy, yield, and economic implications of European corn borer and other lepidopteran management, including Bt corn, scouting-based insecticide applications, and unprotected refuge. Various combinations of pest risks, pest complexes, and management outcomes will be investigated.
The research conducted and information generated will be used to develop multiple media materials for use in educational efforts. Meetings will be held with producers, industry, consultants, and regulators to discuss findings and share information and ideas to enhance policy and regulatory decisions. Newsletters, traditional extension materials, Web pages, scientific publications, adoption surveys, and position statements will be used to disseminate information to the agricultural and public sectors.
NC-205 membership will continue providing science-based information to the Environmental Protection Agency (EPA) and other stakeholders so appropriate and informed regulatory decisions can be made. NC-205 has a history of participating in public policy debates concerning transgenic corn (EPABSAP 1998, NC-205 Supplement 2, EPA-USDA Chicago IRM meeting, e.g., Hellmich 2000; Higgins and Hurley 2000) and is viewed as a highly qualified and unbiased source of research-based knowledge. We will continue to produce and revise videotapes and printed outreach documents such as NCR-327, European Corn Borer: Biology and Management, and NCR-602, Bt Corn and the European Corn Borer: Long-Term Success Through Resistance Management. We also will continue our dialogue with grower organizations and private industry.