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over 700000 acres of sweet corn are grown in the United States for


over 700000 acres of sweet corn are grown in the United States for

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									Insecticide Resistance Action Committee

IRAC U.S. Supports Pyrethroid Resistance Monitoring for Corn Earworm, Helicoverpa zea, in North America Bill Hutchison, Dept. of Entomology, University of Minnesota, St. Paul, MN The corn earworm (CEW), Helicoverpa zea (Boddie), also known as the tomato fruitworm and cotton bollworm, is a highly mobile pest of numerous crops throughout North America, causing millions of dollars in damage and excessive control costs each year. In the Midwestern U.S., H. zea is an economic pest of several high-value crops including: sweet corn, tomatoes, snap beans, peppers and seed corn. Historically, the synthetic pyrethroids have provided cost-effective for CEW management, typically providing >90% control of larvae in sweet corn. However, beginning in 2000-2001, as indicated by smallplot sweet corn trials in Minnesota and Wisconsin, all labeled pyrethroids provided only 35-45% control. In 2005, control for four commonly used pyrethroids (Baythroid, Capture, Mustang-Max, Warrior) averaged 19.3 to 37.3% (mean of 5 trials; 4 states). It is important to note that although small-plot trials (treated by ground application) are not equivalent to large-scale commercial fields (treated aerially), the consistently low larval control observed in small plots is cause for concern about the potential for control problems in future years. In addition to field results, the survival of moths exposed to the standard cypermethrin (5 µg), using the Adult Vial Test (AVT), indicated high survival rates (30-60%); these levels are similar to recent AVT results from Louisiana, Texas and other likely origins of moths that migrate north each summer. In response to the increasing concerns about pyrethroid susceptibility in CEW, IRAC-U.S., funded a twoyear project (2006-2008) to support a significant geographic expansion of CEW moth flight monitoring, and pyrethroid resistance monitoring. Related to these objectives, a primary goal was to develop new, consistent standards for moth flight monitoring, mapping and resistance monitoring. IRAC also provided initial funding to support an interdisciplinary and private/public sector partnership to begin to develop a practical CEW migration forecasting system, that would provide real-time “advance warnings” of lateseason flights in the northern U.S. In the 2nd year of the project, funding will also support a new educational publication for long-term CEW management and IRM recommendations.

During 2006, significant progress was made under each of the proposed objectives, including:  By July of 2006, a greatly expanded network of cooperators was in place for expanding the CEW Moth Flight Monitoring program and for timely reporting data via new webform (ZEA MAP web site: )  Over 40 cooperators, including 25 contacted by Len Dobbins, FMC Corp., participated in the resistance monitoring effort, using cypermethrin at either a single dose (10ug) or a multi-dose AVT, throughout the Midwest and northeastern U.S. Over 4,700 moths were collected and assayed. Survival at 10ug cypermethrin was <1.5% overall, with no significant “hot spots” detected.

Insecticide Resistance Action Committee

Despite the positive results shown from the AVT assays, and although no widespread reports of control failures were reported, CEW larval control in small-plot trials, as well as one large aerial test in commercial sweet corn, continued to show low efficacy with control ranging from 3550%. A meeting to develop a new framework for modeling CEW migration from the southern to northern U.S. has been planned for late June 2007, to be held at Pennsylvania State Univeristy.


All proposed objectives will continue in 2007-2008, with additional studies conducted to better understand how AVT results vary in contrast to larval selection pressure in individual fields.

Finally, a symposium was held in March 2006, at the annual North Central Branch, Entomological Society of America meetings, to review the status of pyrethroid resistance in the U.S., and develop objectives for future research. Seven papers from the symposium have been accepted for publication in the on-line journal, Plant Health Progress and will be published during the summer of 2007 (see ZEAMAP web site, for updates). In summary, the funding from IRAC also helped to leverage additional funds from the USDA-CSREES, North Central Integrated Pest Management Center (Michigan State University), the Rapid Response Fund, from the University of Minnesota, the IPM Program of the Minnesota Dept. of Agriculture, and generate considerable in-kind support from FMC Corp. (AVT monitoring) as well as additional university and extension staff. Continued effective management of CEW will depend upon continued collaboration and networking of extension, industry and research personnel to facilitate multi-state resistance monitoring, multi-state research, and the development of new alternatives for CEW management. We anticipate that the expanded utility of this on-line system will improve communication among researchers and provide timely IPM recommendations by extension educators in the regions most affected by continued pyrethroid resistance in CEW. Project Updates, see: Hutchison, W.D., and Burkness, E.C. 2006. Zea-Map: The H. zea network for insecticide resistance monitoring and management in North America. University of Minnesota, St. Paul. On-line:

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