Plant Biotechnology: Current and Potential Impact For Improving Pest Management In U.S. Agriculture An Analysis of 40 Case Studies June 2002

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1 Plant Biotechnology: Current and Potential Impact For Improving Pest Management In U.S. Agriculture An Analysis of 40 Case Studies June 2002 Insect Resistant Field Corn (3) Leonard P. Gianessi Cressida S. Silvers Sujatha Sankula Janet E. Carpenter National Center for Food and Agricultural Policy 1616 P Street, NW Washington, DC Phone: (202) Fax: (202) ncfap@ncfap.org Website: Financial support for this study was provided by the Rockefeller Foundation, Monsanto, The Biotechnology Industry Organization, The Council for Biotechnology Information, Grocery Manufacturers of America, and CropLife America.

2 30. Field Corn Insect Resistant (3) Production All 48 coterminous states have corn acreage and, in many states, corn is the single most important crop in terms of acreage and production value. Corn production is centered in the Midwest, where ten states account for 85% of the US acreage and production. Individually the states of Illinois and Iowa account for more than 10 million acres of corn each. Table 30.1 contains estimates of field corn production and acreage for 18 major corn-producing states for Rootworm Corn rootworms are the most serious insect pests in field corn in the US. There are four species of corn rootworm found in the U.S.: northern corn rootworm (NCR), western corn rootworm (WCR), southern corn rootworm (SCR), and Mexican corn rootworm (MCR). Rootworms causing significant damage in the eastern and western Corn Belt and some southern states are the NCR and WCR. The SCR occurs in most areas east of the Rocky Mountains, but is only a potential economic threat in southern states where it overwinters [2]. The MCR is found in south central states such as Texas, its range having expanded north from Mexico and Central America [3, 4]. Northern, western and Mexican corn rootworms have similar life cycles, producing one generation per year [3, 5]. Adult beetles feed on corn pollen, silks, and other plant parts, as well as pollen from other plants, but adult feeding damage is not normally of economic importance in corn. Significant rootworm damage is caused by feeding of the larvae on corn roots. Adults begin laying eggs in the soil of corn fields in mid to late summer, and the eggs overwinter in the soil. In late spring or early summer, egg hatch begins and emerging larvae feed on corn roots for three to four weeks. Larvae then pupate in the soil and 2

3 emerge as adults in the mid summer, beginning the cycle anew. Whereas adults may feed on plants other than corn, larvae are almost exclusively found in corn, with some minor occurrence in other grass species. Southern corn rootworm overwinters as adults in plant litter [2]. Adults become active in the early spring and lay eggs in the soil in late spring, when corn plants are already in seedling stage [6]. Eggs hatch after one week and feed on corn roots for two to four weeks before pupating. A new generation of adults emerges in mid summer. There may be two or even three generations of SCR per year. Unlike the other corn rootworm species, the SCR has a wide host range. Larvae can be found in the roots of corn, peanuts, alfalfa and cucurbits. Adults, also known as spotted cucumber beetles, are general feeders on almost 300 plant species. Rootworm Damage It has been estimated that rootworms cost U.S. corn growers $1 billion annually in control costs and crop losses. Extension entomologists in 22 states surveyed in 1992 reported that without treatment, yield loss caused by corn rootworm infestations ranged from 0% to 15%, but could be as high as 50% [1]. Where they occur, WCR, NCR, and MCR are considered primary pests because of their high potential to damage corn roots. In southern states where these rootworm species do not occur but where SCR is present, the greater risk posed to corn production by other insect pests also present generally relegates SCR to being of secondary importance. Generally, young rootworm larvae tend to feed on root tips, tunneling toward the plant base, destroying finer roots and root hairs which absorb water and nutrients [5]. Older larvae tend to feed on the larger roots closer to the plant stalk, consuming more root mass than the younger larvae. Damage to roots from rootworm larval feeding reduces the plant s ability to absorb and distribute water and nutrients from the soil. Loss of root mass to rootworm feeding 3

4 makes plants susceptible to lodging, which may or may not kill the plant. Lodging that does not kill the plant increases direct yield losses during harvest by making mechanical harvesting more difficult, and reduces yield by reducing the amount of light the plant is able to intercept [7]. Lodging significantly increases the time needed to harvest a field. In addition to lodging, another way larval rootworm feeding causes indirect losses to corn is by increasing the incidence of root rots [2, 5]. Rootworm larvae may spread disease pathogens from infested plants to healthy ones, and feeding wounds created by the larvae may provide entry points for pathogen infection. The economic impact of root feeding by corn rootworm larvae can vary with the circumstances of the infestation, such as how many larvae are present per plant, the age of the plant when damage occurs, soil fertility and moisture level, and the ability of the corn variety to regenerate roots [7, 8, 9, 10]. Extrapolating yield losses from root damage is difficult because of these variations. Rootworm Control For three out of the four corn rootworm species damaging U.S. corn, crop rotation has provided adequate protection in most corn growing areas. Western, northern and Mexican corn rootworm adults normally lay eggs in corn fields and they do not hatch until the following season, they have only one generation per year, and their larvae only feed on corn roots. Consequently, rotating corn with other crops can effectively break the rootworm life cycle and keep rootworm populations and damage down in the corn rotation. The most common rotation alternates corn with soybean. Minimizing volunteer corn plants in non-corn rotations is also important for reducing rootworm populations in the subsequent corn planting. Even though crop rotation is the best management strategy for control of WCR, NCR, and MCR, a large percentage of U.S. corn acreage is not rotated but rather is planted to continuous corn. There are several possible reasons a grower may plant continuous corn and risk rootworm damage [1]. Growers who produce corn as feed for their own 4

5 livestock may find it more economical to plant a steady supply of corn rather than purchase feed offsite during the non-corn rotation years. Corn is more effective at preventing erosion than is soybean, so growers with sloping land and soil erosion concerns may find the soil conservation benefits of continuous corn outweigh the risk of rootworm damage. Continuous corn plantings are at higher risk of rootworm infestation and damage because they provide a continuous breeding ground for rootworm. Continuous corn is protected against rootworm damage by soil applied insecticides. Monitoring root damage and adult rootworm populations in corn one year can help determine the presence of a larval rootworm infestation and whether insecticides for larval rootworm control in the following corn planting will be needed. The percentage of continuous corn acreage in the eastern and western Corn Belt states treated with insecticides ranges from 7% to 100% [1]. Crop rotation is not an effective management practice for SCR because of its wide host range, because egg laying occurs soon after corn fields have been planted and multiple generations are produced within the same corn field. Other cultural practices are recommended for SCR management. Plowing or disking at least one month before planting corn deters further egg-laying in the field. Early planting and high seeding rates, and other agronomically favorable practices ensure a good stand that may better tolerate rootworm feeding damage. Soil applied insecticides are the primary tool for protection against SCR feeding [2], but SCR is not generally the primary target of soil applied insecticides because in areas where it occurs other soil borne insect pests, pose a greater and more consistent threat. Corn Rootworm Insecticides Efficacy of insecticides applied to the soil for larval rootworm control is affected by a number of interacting factors [3, 11, 12]. These include properties of the insecticide, such as toxicity, water solubility and volatility, and the method and timing of application, as well as parameters of the rootworm larvae population. Coordinating insecticide 5

6 presence and activity in the root zone with rootworm egg hatch is critical. Generally, insecticides applied at planting will coincide with egg hatch, unless planting is very early or other factors decrease insecticide activity and availability after it has been applied. Soil conditions such as type, moisture level and temperature, and presence and composition of insecticide-degrading microbes in the soil can greatly influence insecticide activity. Soil that is too warm, too dry or too wet will decrease insecticide activity and availability. Historically, insecticides for rootworm control that may be effective upon introduction within a few years become inconsistent and ineffective in areas of repeated use [3]. Declining efficacy of an insecticide against rootworm larvae, or a reduction in the consistency of its performance, may result from a number of factors, including changes in the soil properties which affect insecticide degradation and dissipation, or development of greater insecticide tolerance in the rootworm which has been associated with broadcast application of insecticides. The first soil applied insecticides used against corn rootworm larvae were chlorinated hydrocarbons such as benzene hexachloride and DDT. They provided efficient rootworm larvae control for about two decades, until the 1960s [3]. Carbamates such as bufencarb and carbofuran were introduced for rootworm control in the 1960s and 1970s, but became inconsistent performers within a decade of introduction. Organophosphates were introduced for rootworm control around Currently, larval rootworm control is dominated by other organophosphates and pyrethroids. Insecticides currently recommended for rootworm management include chlorethoxyfos, chlorpyrifos, cyfluthrin, bifenthrin, fipronil, terbufos, tefluthrin, tebupirimphos and phorate. Beginning in the late 1970 s, insecticide use for corn rootworm management declined as research showed that rotating out of corn for one year was economically effective and first year corn did not require insecticide treatment for rootworm [14]. Figure 30.1 shows soil insecticide use trends in Illinois from 1978 to 1990 [15]. 6

7 The estimated use, in 1997, of insecticides for rootworm by state is shown in Tables 30.2 and Approximately 12 million pounds of soil-applied insecticides were used in 1997 to control rootworms on 18 million acres in the 18 states. The high cost of broadcast applications of soil insecticides is prohibitive in field corn, so banded or furrow applications are made [16]. Insecticides used in banded applications are applied over a just-planted row in a 7-8 inch band and incorporated by the planter press wheel and spring-tines or drag chains pulled by the planter [17]. Furrow applied insecticides are placed in the furrow with seeds at planting. Banded or furrow applications protect the central root zone but leave the peripheral area between rows unprotected. Peripheral root pruning may occur in these unprotected zones, but resulting damage or yield loss is usually not economically significant. In 1992, Extension Specialists estimated yield losses to corn rootworm with a soil insecticide application to be 1% to 2% [1]. Large plot insecticide trials performed by Purdue University researchers from 1991 to 2000 indicate corn rootworm soil insecticides prevented an average yield loss of 6.5% in comparison to untreated control plots [16]. Insecticides applied to the soil at planting may be either granular or liquid formulations. For granular applications, the applicator opens the insecticide package and pours the insecticide into a hopper box, specially designed for pesticide application, which is mounted on the planter. Material from the hopper box feeds through tubes that deliver it either with the seed in furrow, or in a band across the row after seed has been planted and covered but before the press wheel goes over it. The hopper box delivery system must be carefully calibrated at each use, a time-consuming process that if done incorrectly, may reduce pesticide efficacy. Liquid applications are often sold in closed box systems that are mounted on the planter and feed into a system of delivery tubes. The closed box systems reduce applicator exposure, but most still require equipment calibration. Whether granular or liquid formulations are used at planting, the application process complicates the planting process, costing the grower time and money. When planting a field, stops must be made periodically to refill the planter with seed. If insecticides are 7

8 applied as well, additional stops must be made to refill the hopper box or to replace the closed liquid insecticide delivery system when material runs out. Secondary Soil Insect Pests Soil insecticides applied for corn rootworm larvae control also help control other soilborne insect pests in corn, such as wireworms, black cutworms, and white grubs [1]. These pests are considered secondary pests because they are capable of causing economic damage but do not do so every year or on a large percentage of the acreage [18]. When and where they do occur, though, they have devastating consequences. Recent trends in frequency of damage from these secondary pests suggest that they may become an annual concern for many corn growers. Wireworms attack seeds or drill into seedling stems below the soil line, weakening or killing plants. White grubs chew on roots and root hairs, reducing plant vigor or killing the plant. Wireworms and white grubs are widespread pests with long life cycles of several years, and high infestations are difficult to predict. Black cutworms feed on leaves, but economic damage occurs when older larvae feed on stems, cutting the plants off at or near the soil surface. Black cutworms are widespread but sporadic pests, causing severe stand reduction where epidemics occur [1]. Timing and location of infestations of these secondary pests are difficult to predict, and rescue treatments applied after infestations are detected are often ineffective [18]. Consequently, insecticides applied to the soil at or near planting are recommended for corn acreage potentially at risk of attack by these pests. An alternative to applying soil insecticides is to purchase seed pre-treated with insecticides. Available seed treatments include one that uses the active ingredient tefluthrin, and two that use imidacloprid, each at a different rate. The lower rate imidacloprid seed treatment is marketed for control of secondary soil insect pests, and the higher rate imidacloprid is marketed for rootworm protection. University studies in Iowa and Illinois found that seed treatments for rootworm provided inadequate protection 8

9 under moderate to high rootworm pressure, and their use is not recommended at this point [13, 19]. Seed treatments may provide a viable alternative to soil insecticides for management of secondary pest damage [18]. In an evaluation of the efficacy of several seed treatments, on wireworm, tefluthrin and imidacloprid provided control that was statistically similar and numerically intermediate in terms of damage compared to conventional soil-applied insecticides (Table 30.4) [29]. Rotation-Resistant Rootworm Crop rotation has failed to control CRW damage in some areas, resulting in economic losses in first year corn. New biotypes of western and northern corn rootworm have appeared that have developed mechanisms of resistance to crop rotation. Table 30.5 lists the estimated corn acreage at risk of infestation with these new rootworm variants. Normally in a corn/soybean rotation, WCR and NCR adults lay eggs in corn fields, the eggs diapause through the winter and when they hatch in spring the field is planted to soybeans, on which the larvae cannot survive. In addition, adult rootworm beetles will not lay eggs in fields planted to soybeans, so by the time corn is planted the following year, the field is free of rootworms. The new biotype of WCR beetles appearing in eastern Illinois, northern Indiana and parts of Michigan (Figure 30.2), will lay eggs in soybean fields, so that egg hatch the next season coincides with a corn rotation [20]. WCR in these areas also lay eggs in corn; however, they prefer to lay eggs in late-planted corn. Although rotation resistant WCR has been assumed to be present in Ohio, monitoring has failed to confirm the problem [38]. Trapping studies show WCR beetles, particularly females, fly between cornfields and soybean fields throughout the day [21]. Problems managing NCR with rotation first appeared in the first half of the century, but frequency, severity, and scope of the problem have increased in the last few decades [22]. In South Dakota, Minnesota, Iowa, and Nebraska (Figure 30.3), NCR have been found whose eggs exhibit extended diapause [22]. The new NCR biotype diapauses for two 9

10 winters, missing the soybean rotation and hatching out in time to feed on the next corn rotation. Reductions in soil insecticide use for rootworm control seen since the 1970s (Figure 30.1) are at risk of being reversed as growers respond to the new rotation-resistant rootworm biotypes with increased insecticide use in rotated corn [23]. Indeed, a trend towards increasing insecticide use in corn in Illinois, where rotation-resistant WCR is the most widespread, is becoming discernable (Figure 30.4). Bt Corn for Rootworm Two new transgenic corn varieties have been developed which produce Bt proteins toxic to corn rootworm beetles. One variety, developed by Monsanto, produces the Cry3Bb protein. An application for its registration was submitted to EPA in March, 2001 [24]. The other variety, developed by Dow AgroSciences, Pioneer Hi-Bred, and Mycogen Seeds, produces a different Bt protein and is currently being field tested under EPAgranted experimental use permits [25, 26]. The protein produced by Dow AgroScience s product has not yet been categorized as a Cry protein but is referred to as the PS-149-B1 protein. Both new transgenic varieties were developed to have resistance to corn rootworm species. One potential benefit Bt corn for rootworm protection may offer is more consistent and reliable protection than that provided by soil insecticides. The efficacy of soil applied insecticides is dependent on proper timing and placement, and the environmental conditions that affect insecticide duration in the soil and rootworm larval emergence. If these factors are not in synchrony, the potential soil insecticides have for high level rootworm protection is often compromised, making performance inconsistent. The protection offered by Bt corn for rootworm control is internal and is continually expressed, maximizing consistency of performance and minimizing risk. Monsanto s Bt corn events were evaluated for protection against western and northern corn rootworm [27, 28]. In terms of level of root damage and consistency of protection, 10

11 these transgenic events performed equally well or better than the soil insecticide treatments used for comparisons (Tables 30.6 and 30.7). Estimated Impacts Corn production areas affected by WCR, NCR, and MCR, such as the eastern and western Corn Belt, are at risk of consistent economic losses to rootworm feeding and therefore would be most likely to adopt transgenic corn with rootworm resistance. Areas affected by SCR (southeastern states) apply few insecticides to specifically target SCR, and so are unlikely to widely adopt new technology that specifically targets SCR. It is estimated that acreage likely to be planted to rootworm-protected corn includes corn acreage that is treated with soil insecticides at planting. In addition, corn acreage that is at risk of infestation with rotation-resistant rootworm would also be planted to rootwormprotected corn. Acreage treated in 1997 would include acreage treated for rotation resistant NCR, which has been a problem for corn growers since the 1980 s. However, rotation resistant WCR has become increasingly problematic in recent years and is not reflected in the 1997 insecticide use figures. Therefore, estimated adoption is calculated as the sum of 1997 acres treated plus acreage infested with rotation resistant WCR (Table 30.8). Insecticide treatment may still be needed to manage risk of feeding by secondary pests, especially if their frequency of occurrence continues to increase. This may either be in the form of current soil insecticides applied at planting, or in the form of an insecticide treatment coating the Bt seed. If the cost of insecticide-treated Bt seed is still comparable to the current cost of soil insecticide application, the convenience of having soil insect protection in and on the seed without having to apply a separate insecticide should facilitate its adoption. The insecticide use rate for seed treatment is lower than for soil applied insecticides. The average application rates by state of insecticides used for rootworm control are shown in Table Average application rates for two seed treatments, calculated assuming a 11

12 seeding rate of 30,000 seeds/acre [33], is lb/acre. If rootworm protected Bt corn seed treated with insecticide for control of secondary pests replaces soil insecticide applications for rootworm and secondary pest control, insecticide use by state would decline by between 0.4 and 1.3 lbs/acre. Assuming that Bt corn for rootworm control provides protection equivalent to that achieved with soil insecticides, no change in yields is projected. Future research should indicate whether the increased consistency Bt corn is expected to provide will increase aggregate yields as well. The aggregate impact of adoption of Bt corn for rootworm is estimated to be a 14 million lbs reduction in insecticides (Table 30.9). 12

13 Table 30.1 Corn for Grain: 2000 State Harvested (000A) Yield (BU/A) Production (Million Bushels) Price Per Bushel ($) Value of Production (Million $) CO IL IN IA KS MD MI MN MO NE NY ND OH OK PA SD TX WI Total US Total Sources: [31, 39] 13

14 Table 30.2 Corn Rootworm Insecticide Use in 1997 by State and Active Ingredient Percent of Acres Treated Application Rate (lbs AI/acre) Acres Treated Total Pesticide Use (lbs) State Active Ingredient Colorado CHLORETHOXYFOS ,161 5,081 CHLORPYRIFOS ,637 6,564 PHORATE ,161 12,194 TEFLUTHRIN , TERBUFOS , ,655 Colorado Total 211, ,306 Illinois CHLORETHOXYFOS ,584 34,653 CHLORPYRIFOS , ,023 CYFLUTHRIN + TEBUPIRIMPHOS ,584 20,575 PHORATE , ,204 TEFLUTHRIN ,043 68,224 TERBUFOS , ,655 Illinois Total 2,577,347 1,519,335 Indiana CHLORETHOXYFOS ,575 53,532 CHLORPYRIFOS , ,609 CYFLUTHRIN + TEBUPIRIMPHOS ,100 60,670 PHORATE ,763 61,896 TEFLUTHRIN ,100 35,688 TERBUFOS , ,626 Indiana Total 2,013,028 1,068,020 Iowa CHLORETHOXYFOS ,737 37,878 CHLORPYRIFOS ,680 1,044,366 CYFLUTHRIN + TEBUPIRIMPHOS ,106 49,715 PHORATE , ,634 TEFLUTHRIN ,843 71,021 TERBUFOS , ,759 Iowa Total 2,260,840 1,682,372 Kansas CHLORPYRIFOS ,364 90,688 TEBUPIRIMPHOS ,450 10,198 TEFLUTHRIN ,899 18,828 TERBUFOS , ,935 Kansas Total 577, ,649 Maryland 14

15 CHLORPYRIFOS ,616 45,218 TEFLUTHRIN ,857 4,986 TERBUFOS ,971 10,669 Maryland Total 106,444 60,873 Michigan CHLORETHOXYFOS ,041 7,687 CHLORPYRIFOS , ,756 PHORATE ,041 46,600 TEFLUTHRIN ,166 15,373 TERBUFOS , ,693 Michigan Total 578, ,109 Minnesota CHLORPYRIFOS , ,166 PHORATE , ,317 TEFLUTHRIN ,633 21,331 TERBUFOS , ,974 Minnesota Total 826, ,787 Missouri CHLORETHOXYFOS ,069 8,171 CHLORPYRIFOS , ,452 PHORATE ,534 24,513 TEBUPIRIMPHOS ,069 4,596 TEFLUTHRIN ,534 1,277 TERBUFOS ,534 22,981 Missouri Total 330, ,989 Nebraska CHLORETHOXYFOS ,891 42,445 CHLORPYRIFOS , ,402 CYFLUTHRIN + TEBUPIRIMPHOS ,018, ,355 PHORATE , ,128 TEFLUTHRIN ,127 67,913 TERBUFOS , ,620 Nebraska Total 3,149,451 1,545,863 New York CHLORPYRIFOS , ,128 TEFLUTHRIN , ,910 TERBUFOS ,602 24,184 New York Total 901, ,222 North Dakota PHORATE ,161 48,310 TEFLUTHRIN , TERBUFOS , ,099 North Dakota Total 126, ,301 Ohio 15

16 CHLORETHOXYFOS ,315 34,130 CHLORPYRIFOS , ,636 PHORATE ,553 35,553 TEFLUTHRIN ,525 46,218 Ohio Total 906, ,537 Oklahoma CHLORPYRIFOS TEFLUTHRIN TERBUFOS Oklahoma Total Pennsylvania CHLORPYRIFOS , ,038 CYFLUTHRIN + TEBUPIRIMPHOS ,909 11,720 PHORATE ,558 14,558 TEFLUTHRIN ,585 14,558 TERBUFOS ,117 31,155 Pennsylvania Total 427, ,030 South Dakota CHLORETHOXYFOS ,832 17,416 CHLORPYRIFOS , ,641 PHORATE , ,410 TEFLUTHRIN ,665 9,753 TERBUFOS , ,933 South Dakota Total 928,281 1,235,153 Texas CHLORPYRIFOS ,780 50,215 TERBUFOS , ,998 Texas Total 552, ,213 Wisconsin CHLORETHOXYFOS ,910 11,506 CHLORPYRIFOS , ,060 PHORATE ,910 69,753 TEFLUTHRIN ,552 32,360 TERBUFOS , ,721 Wisconsin Total 1,137, ,399 Source: Calculated from [30]. Assumes 85% of chlorpyrifos use is targeted at rootworms. 16

17 Table State Summary of Corn Rootworm Insecticide Use in 1997 Total Acres Pesticide Application State Treated (000) Use (000lbs) Rate (lbs/acre) Source: See Table 30.2 Colorado Illinois 2,577 1, Indiana 2,013 1, Iowa 2,261 1, Kansas Maryland Michigan Minnesota Missouri Nebraska 3,149 1, New York North Dakota Ohio Oklahoma Pennsylvania South Dakota 928 1, Texas Wisconsin 1, Total

18 Table Wireworm Insecticide Evaluation Active Ingredient Insecticide Rate Placement % Damage Terbufos Counter 20CR 1.2 Furrow 9 a Terbufos Counter 20CR 1.2 T-band 12 a Terbufos Counter 20CR 0.6 Furrow 13 a Chlorethoxyfos Fortress 5G 0.15 Furrow 14 a Tefluthrin Force 3G 0.15 Furrow 17 a Tebupirimphos Aztec 2.1G 0.07 Furrow 25 ab Tefluthrin ProShield ST Seed Trt 27 ab Tefluthrin Force 3G 0.15 T-band 27 ab Tebupirimphos Aztec 2.1G 0.14 Furrow 28 ab Imidacloprid Gaucho ST 0.16 mg/seed Seed Trt 29 ab Imidacloprid Adage ST 50 g/100 kg seed Seed Trt 31 ab Fipronil Regent 4SC 0.12 Furrow 39 ab Fipronil Regent 4SC 0.09 Furrow 44 ab Check 72 b Notes: Results followed by same letter are not statistically different. Treatment rates as oz. a.i./1000 row feet. Source: [29] 18

19 Table Estimated Corn Acreage at Risk of Infestation with Rotation-Resistant Corn Rootworm. Western Corn Rootworm Northern Corn Rootworm State Acreage State Acreage Illinois 3,259,520 Iowa 3,287,200 Indiana 2,830,880 Minnesota 2,279,280 Michigan 309,600 South Dakota 1,504,000 Nebraska 572,800 Total 6,400,000 Total 7,643,280 Note: Calculated assuming 80% of corn acreage in counties at risk for rotation resistant CRW populations are rotated corn. Source: [11,22, 35, 36, 37] Table Root Ratings for Bt Corn Events Versus Conventional Insecticides Treatment Counter 20CR (Terbufos) Force 3G (Tefluthrin) Lorsban 15G (Chlorpyrifos) Event A Event B Event C Event D Untreated Root Rating 1.6 d 1.6 d 2.0 cd 2.2 c 2.6 b 2.2 c 1.0 e 4.2 a Root ratings on a 1-6 scale, with 1 = no observable rootworm feeding scars present and 6 = three or more full nodes of roots pruned [32]. Means followed by the same letter within a column are not significantly different Source: [27] 19

20 Table Rootworm Control Efficacy of Bt Corn Events Versus Conventional Insecticides Node-injury Treatment Full Partial (%) % Consistency a Counter 20CR (Terbufos) 0 37 ab 45 bc Event A 0 7 a 95 a Event B 0 2 a 100 a Event C 0 2 a 100 a Event D 0 1 a 100 a Force 3G (Tefluthrin) 0 22 ab 75 ab Lorsban 15G (Chlorpyrifos) 0 64 b 20 c Untreated check 0 65 b 25 c Means followed by the same letter within a column are not significantly different. Nodeinjury scale: 0.01-no feeding damage; 1-one node, or the equivalent of an entire node, eaten back to within approximately 2 inches of the stalk., etc. Damage in between complete nodes destroyed is noted as the percentage of the node missing. a Percent consistency equals the percentage of times a treatment limited feeding damage to ¼ node or less. Source: [28] 20

21 Table 30.8 Estimated Adoption of Bt Corn for Rootworm by State Rotation Resistant State Acreage Treated in (000A) WCR Acreage 2 (000A) Total Adoption (000A) CO IA 2, ,261 IL 2,577 2,934 5,511 IN 2,013 2,548 4,561 KS MD MI MN MO ND NE 3, ,149 NY OH OK PA SD TX WI 1, ,138 17,641 5,761 23,402 1 See Table Rotation-resistant acreage with economic levels of rotation resistant WCR calculated assuming 90% of rotation resistant acreage is treated (see Table 30.5). 21

22 Table 30.9 Estimated Impacts of Bt Corn for Rootworm by State Pesticide Use Reduction 2 Adoption Acreage 1 (lbs AI/yr.) CO IA IL IN KS MD MI MN MO ND NE NY OH OK PA SD TX WI TOTAL 23,402,000 14,496,000 1 See Table Calculated with average use rates shown in Table 30.3 minus.013 lb/a to account for seed treatment use. 22

23 Figure Trends in soil insecticide use on corn in Illinois ( ) 100 % crop treated Source: [15] 23

24 Figure Areas with Rotation Resistant Western Corn Rootworm Sources: [11,22,35,37] 24

25 Figure Areas with Rotation Resistant Northern Corn Rootworm Source: [22] 25

26 Figure Insecticide Use in Illinois Corn ( ) % Acres Treated Source: [34]

27 References: 1. Pike, D.R., et al., Biologic and Economic Assessment of Pesticide Use on Corn and Soybeans, USDA NAPIAP Report Number 1-CA-95, North Carolina State University, Insect and Related Pests of Field Crops, Publication AG-271, Available on the internet at 3. Levine, E. and H. Oloumi-Sadeghi, Management of Diabroticite Rootworms in Corn, Annual Review of Entomology 36: , Jones, G.D. and J.R. Coppedge, Foraging Resources of Adult Mexican Corn Rootworm (Coleoptera: Chrysomelidae) in Bell County, Texas, Journal of Economic Entomology 93(3): , University of Missouri, Corn Insect Pests: A Diagnostic Guide, UM Extension, Available on the internet at 6. Morrison, W.P., et al., Managing Insect and Mite Pests of Texas Corn, Texas A&M University Agricultural Extension Service Bulletin B-1366, Available on the internet at 7. Spike, B.P. and J.J. Tollefson, Yield Response of Corn Subjected to Western Corn Rootworm (Coleoptera: Chrysomelidae) Infestation and Lodging, Journal of Economic Entomology 84(5): , Turpin, F.T., et al., Edaphic and Agronomic Characters that Affect Potential for Rootworm Damage to Corn in Iowa, Journal of Economic Entomology 65(6): , Spike, B.P. and J.J. Tollefson, Relationship of Plant Phenology to Corn Yield Loss Resulting from Western Corn Rootworm (Coleoptera: Chrysomelidae) Larval Injury, Nitrogen Deficiency, and High Plant Density, Journal of Economic Entomology 82(1): , Spike, B.P. and J.J. Tollefson, Relationship of Root Ratings, Root Size, and Root Regrowth to Yield of Corn Injured by Western Corn Rootworm (Coleoptera: Chrysomelidae), Journal of Economic Entomology 82(6): , 1989.

28 11. Edwards, C.R., et al., Managing Corn Rootworms 2002, Purdue University Cooperative Extension Service publication E-49, Available on the internet at Gray, M.E, et al., Planting Time Application of Soil Insecticides and Western Corn Rootworm (Coleoptera: Chrysomelidae) Emergence: Implications for Long-Term Management Programs, Journal of Economic Entomology 85(2): , Gray, M. and K. Steffey, Seed Treatments and Consistent Corn Rootworm Control: Not a Proven Strategy, Pest Management and Crop Development Bulletin Number 24, University of Illinois at Urbana-Champaign, When Farmers Are Bugged, Illinois Research, Winter 1993/ Pike, D.R., et al., Pesticide Use in Illinois: Results of a 1990 Survey of Major Crops, University of Illinois at Urbana-Champaign Cooperative Extension Service, Edwards, C.R., Purdue University, personal communication. 17. Corn Rootworm Management, University of Illinois at Urbana-Champaign IPM Insect Information Sheet Number 3. Available on the internet at Steffey, K.L. and M.E. Gray, Should We Expect More from Wireworms, White Grubs, grape Colaspis, et al. in the Future?, Proceedings of the Illinois Crop Protection Technology Conference, January 5-6, Proshield, Prescribe Don t Make the Grade Against Rootworms, Progressive Farmer, February, Spencer, J.L., et al., Western Corn Rootworm Injury in First-Year Corn: What s New, Proceedings of the Illinois Crop Protection Technology Conference, January 6-7, Spencer, J., et al., Western Corn Rootworms in the 21 st Century: New Research on an Old Problem, Proceedings of the Illinois Crop Protection Technology Conference, January 9-10, Ostlie, K.R., Extended Diapause, Crop and Soils Magazine, June-July, Gray, M.E. and K.L. Steffey, Corn Rootworm (Coleoptera: Chrysomelidae) Larval Injury and Root Compensation of 12 Maize Hybrids: an Assessment of the Economic Injury Level, Journal of Economic Entomology 91(3): ,

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30 37. Ratcliffe, Susan T., et al., 2001 No. 1 - Western Corn Rootworm: Diabrotica virgifera virgifera LeConte wcornr/wcornr.html 38. Bruce Eisley, Ohio State University, personal communication. 39. USDA, Crop Values 2000 Summary, National Agricultural Statistics Service, February