NCCC046: Development, Optimization, and Delivery of Management Strategies for Corn Rootworms and Other Below-ground Insect Pests of Maize.
Statement of Issues and Justification
Corn rootworms are considered to be the primary insect pest complex of maize in most portions of the United States Corn Belt. Damage from larval feeding by these insects and associated control costs has been estimated at approximately 1 billion dollars annually for American corn producers. Traditional management options include the use of insecticides at levels surpassing those of any other insect pest of corn. Species makeup of this complex can vary throughout the United States; however, corn root damage and management options are similar. The western corn rootworm, Diabrotica virgifera virgifera LeConte, and northern corn rootworm, D. barberi Smith and Lawrence, are often considered the most serious of these insect pests attacking corn in the Midwestern United States. With movement of the Mexican corn rootworm, D. virgifera zeae Krysan and Smith, into Texas, corn from the Rocky Mountains to the Atlantic Ocean and from Texas into southern Canada is attacked by this pest complex. This wide distribution throughout most of North America allows this pest complex to transcend corn production systems and crop-use patterns. For instance, rootworms often infest irrigated corn in the west and dryland production systems further east. These insects attack corn that will be used for on-farm feed (grain or silage), as well as grain that will be sold for off-farm use (e.g., food, feed, and industrial manufacturing). The diverse geographies, environments, and production systems that this pest complex can exploit make it appropriate to coordinate research throughout its range. In many of these areas corn rootworms are considered to be a key pest for corn producers, but they are not the only insects that can attack the below-ground portions of maize plants. These other insect pests (e.g., grubs, wireworms, seedcorn beetles, seedcorn maggots, and grape colaspis, etc.) are sometimes referred to as "secondary pests" and can cause serious economic damage to corn. Damage caused by these pests can be highly variable depending on environmental conditions and infestation level. In some corn production areas, their injury can rival or even surpass that caused by corn rootworms. They are often linked with corn rootworms in relation to management because chemical control tools used for the primary target are often sufficient to control many of these secondary pest species in the soil.The original corn rootworm Multistate Research Coordinating Committee was approved in 1964 as a NCR project, and the committee has operated continuously since then. The intent of the project was to "study, on a regional basis, the biology of the corn rootworm complex in relation to current and projected cultural practices and to identify vulnerabilities of the pests that could be used as control measures benefiting farmers in the North Central Region." At that time, the northern corn rootworm was an economic pest in the central Corn Belt and the western corn rootworm had just begun its spread out of Kansas and Nebraska. By 1964, the western corn rootworm had become established in South Dakota, and southern Minnesota, and the western half of Iowa. The "official" membership of the earlier research coordinating committees came from 12 north central state agricultural experiment stations and the USDA-ARS Northern Grain Insects Research Laboratory in Brookings, SD. As the western corn rootworm continued to spread, scientists from the newly infested corn-growing states and Canadian provinces began attending the committee's meetings as "associate" members. Several of these individuals have gone through CSREES to become "Official" members. The 2001 renewal proposal of the corn rootworm Multistate Research Coordinating Committee contained internal and external linkages to resources from nearly all corn production areas currently infested by this insect pest complex in the United States and Canada.
As stated previously, the original intent of the previous committees was to study the biology of the corn rootworm complex to identify vulnerabilities of the pests that could be exploited for their control. Pooling data across states/provinces has generated several important management decision guidelines involving chemical control tools. Examples of tangible results that were achieved and delivered to growers because of regional coordination include the following: 1) an understanding of how repeated applications of carbamate insecticides to some soils can result in an accelerated rate of degradation by soil microbes that diminishes the insecticides' effectiveness; 2) by combining data across states, a large multistate database with differing environments and production systems was generated to demonstrated that the application rate of many insecticides used could be safely reduced by 25%, thus, lowering grower input costs and maintaining effective pest control; and 3) the concept of controlling adult corn rootworms with reduced rates of insecticides before females lay eggs was refined and demonstrated across a variety of Midwestern corn production systems.
Advances to date have not eliminated the need for regional coordination of corn rootworm research because of changes in corn rootworm biology, pest management technologies, and regulatory issues. A cultural management practice of crop rotation has been used on millions of acres throughout North America for over a century. The more common two-year crop rotation no longer guarantees effective rootworm control. Rotational resistance exists at levels in some states that force producers to seek alternative control measures. For example, the northern corn rootworm has the ability to undergo extended/prolonged egg diapause in parts of SD, NE, MN, IL, and IA. This adaptation allows the insect to have a two-year lifecycle. Eggs remain dormant and bypass the season when corn roots are unavailable on land planted to an alternate nonhost crop, then hatch in the succeeding year when fields are rotated back to corn. Another rotational resistance mechanism involves the western corn rootworm, and is a major management challenge for many growers in the eastern portion of the north central Corn Belt region. First detected in fields on both sides of the Illinois and Indiana border, females of this species have altered their behavior by laying eggs in non-corn habitats (e.g., soybeans which is the crop most commonly rotated with corn). This behavioral variant of the western corn rootworm has spread into Michigan and Ohio, and has been most recently detected in eastern portions of Iowa and Minnesota. New insecticide materials designed for application as seed coats for preventing larval corn rootworm feeding injury and for protection against secondary soil insects have recently been introduced by the agricultural chemical industry. Before these insecticides can be recommended by state extension specialists and agricultural product vendors, a large public database across several production systems and environments must be generated to determine their effectiveness. The western corn rootworm is again developing resistance to insecticides used in Nebraska. A coordinated monitoring program is needed to determine if the genes for resistance are spreading throughout the rootworm population and how this might affect integrated management strategies. Monsanto Inc. was the first seed company to release a corn rootworm-resistant transgenic hybrid called "YieldGard Rootworm" in 2003. Other major companies are also working toward providing similar transgenic hybrids. The United States Environmental Protection Agency is currently evaluating these potential new transgenic hybrids for limited registration that could be granted in late 2005 which would make them available for planting in the 2006 growing season. To ensure that these newer products of biotechnology are environmentally benign and to prevent or delay the onset of insect resistance to the proteins deployed, the combined expertise of the technical committee has been and will continue evaluating potential environmental impacts and developing resistance management strategies that are compatible with production practices throughout the corn producing areas of the continent.
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