Managing Corn Pests with Bt Corn Fact Sheet No. 0.708 Crop Series|Production by F.B. Peairs* New technology allows us to improve relatively harmless to humans and most non Quick Facts crop varieties by adding genes from other pest species. species. This is useful because we can alter • (Bt) traits, such as insect resistance, that might Q: Are there other types of Bt ? is a soil bacterium that not naturally exist in the crop species, or produces insecticidal toxins. that might be difficult to transfer within the A: Another group of Bt toxins are called crop species using classical breeding vegetative insecticidal proteins, or VIPs. • Genes from Bt can be techniques. One successful application of this VIPs also are considered relatively safe for inserted into crop new technology is the development of corn non pest species, however, other classes to make them capable of hybrids that are resistant to certain insect of toxins produced by Bt have a broader producing an insecticidal pests because of the addition of a gene from spectrum of toxicity. toxins and therefore resistant a natural soil bacterium. Such hybrids are to certain pests. referred to as “transgenic” hybrids, although Q: What is Bt corn? not all transgenic hybrids contain insect • Corn hybrids with one or A: Production of delta endotoxins is resistance traits. more Bt genes (Bt corn) are controlled by a single gene in the bacteria. Although these insect-resistant transgenic resistant to some important Modified versions of these genes can corn hybrids are highly effective in pests. be placed in corn plants. Corn plants controlling insect pests, their use has raised containing the gene can produce delta concerns. The following series of questions • Bt corn hybrids are a highly endotoxin and therefore be toxic to insects and answers provides an overview of these effective and economical that are susceptible to that form of the insect resistant corn hybrids and their use in alternative to conventional protein. pest management. Fact sheet 0.707, Bt Corn: insecticide treatments, if Health and the Environment addresses what targeted pest activity is at bacteria are involved; the insecticidal toxins Q: Why use Bt genes in corn? economically significant they produce; crop transformation; and A: Delta endotoxins sprayed on plants break levels. health and environmental issues that have down quickly when exposed to UV light. developed from the use of this technology. Delta endotoxins produced in the plant are protected from UV light. Also, several major Questions and Answers corn pests are difficult and expensive to control with conventional insecticides, but are susceptible to delta endotoxins produced Q: What is Bt? in plant tissues. And, the biotechnology to A: Bt is shorthand for common soil insert the producing Bt gene into corn inhabiting bacteria called Bacillus is available. thuringiensis. Bt also refers to insecticide products made from these bacteria. Q: Is the entire Bt corn plant toxic? A: It depends. Two factors, the event Q: What does Bt have to do with and the promoter, control where delta insect pests? endotoxins are produced in the plant and A: Some strains of Bt kill insects with in what amounts. Different seed companies toxins called insecticidal crystal proteins use different events and promoters, so their ©Colorado State University or delta endotoxins. They are considered hybrids will be different in what plant tissues Extension. 6/02. Revised 12/14. produce delta endotoxins. www.ext.colostate.edu The insertion event is the physical act * F.B. Peairs, Colorado State University Extension of putting the Bt gene into the corn plant’s entomologist and professor, bioagricultural sciences and pest management. 12/2014 genetic material. This is when the physical Table 1. Types of BT corn. Q: Does each hybrid contain just one event? Bt Event Trade Name*** Toxin Type 5307 Agrisure Duracade Cry3A-Cry1Ab** A: This is true for some hybrids. However, the trend is towards having two events Bt11 Agrisure CB Cry1Ab* each for corn borer, rootworm, and DAS59122-7 Herculex RW , Cry35Ab1** herbicide tolerance in a single hybrid. MIR162 Agrisure Viptera VIP3Aa20* MIR604 Agrisure RW modified Cry3Aa** Q: Will all Bt corn hybrids give the MON810 YieldGard Corn Borer Cry1Ab* same level of control? MON88017 YieldGard VT Rootroom Cry3Bb1**, Cry1A.105, Cry2A6* A: The level of control of targeted pests and the spectrum of control provided MON89034 Yieldgard VT Pro, Genuity VT Double Pro by a hybrid is a function of the event(s) TC1507 Herculex CB (Mycogen, Pioneer) Cry1F*, Cry1Ab* + it contains. It is better to compare insect modified Cry3Aa** control by event rather by hybrid. For Bt11 + MIR604 Agrisure CB/LL/RW, Agrisure 3000GT example, corn borer control can be expected to be similar among hybrids Bt11 + MIR162 Agrisure Viptera 3110 Cry1Ab* + VIP3Aa20* containing the Mon810 event. Bt11 + MIR604 + Agrisure Viptera 3111 Cry1Ab* + VIP3Aa20* + MIR162 modified Cry3Aa** Select hybrids that will work well in your area and ask for insect control data Bt11 + MIR162 + Agrisure Viptera 3220 Cry1Ab* + VIP3Aa20* + TC1507 Cry1F* that are specific for the events that these hybrids contain. MON810 + MON88017 YieldGard VT Triple Cry1Ab* + Cry3Bb1 MON810 + TC1507 Optimum Intrasect Cry1Ab* + Cry1F* Q: Will Bt corn work well in my area? TC1507 + 149B1 Herculex XTRA Cry1F + Cry34Ab1, Cry35Ab1 A: The Bt traits should not affect hybrid MON88017 + Genuity VT Triple Pro Cry3Bb1** + Cry1A.105, performance. If the conventional version MON89034 Cry2A6* of the hybrid works well, the Bt version MON810 + TC1507 + Optimum Intrasect XTRA Cry1Ab* + Cry1F* + should work well too. DAS59122-7 Cry34Ab1, Cry35Ab1** MON88017 + SmartStax Cry1A.105, Cry2A6* + Cry1F* MON89034 + + Cry3Bb1** + Cry34Ab1, Q: Is Bt the only trait genetically DAS59122-7 + TC1507 Cry35Ab1** engineered into corn? 5307 + Bt11 + MIR604 Agrisure Duracade 5122 Cry3A-Cry1Ab*,** + Cry1Ab* + TC1507 + modified Cry3Aa** + A: Other hybrids with genetically Cry1F* engineered traits, such as herbicide 5307 + Bt11 + MIR604 Agrisure Duracade 5222 Cry3A-Cry1Ab*,** + Cry1Ab* resistance and drought tolerance, are + TC1507 + MIR162 + modified Cry3Aa** + available. Many other traits are in Cry1F* + VIP3Aa20* development and will become available in *Targets caterpillars. the future. **Targets rootworms. ***Some may include herbicide tolerance traits, as well. Q: Is corn the only crop genetically engineered with Bt? location of the Bt gene is determined the corn plant, leading to differences among A: No, several other crops have been (which chromosome, what part of the hybrids. modified to produce Bt toxins. However, chromosome, etc). Gene location affects corn and cotton make up most of the where in the plant delta endotoxins are Q: Have VIPs been used in corn? commercial use. produced and how much A: VIP events have been used successfully is produced. Currently, we do not have the for many years in cotton and now are Q: What kind of European corn borer technology to control Bt gene location, so available in corn (Table 1). each event results in plants that differ in control can I expect from Bt corn? where and in how much delta endotoxin is A: Control of first generation is expected produced. Q: How many kinds of Bt corn are to be excellent and possibly better than The promoter is a genetic switch that there? would be expected from a single well- tells the inserted Bt gene when and where A: There are many different Bt corn timed insecticide application. Control of to produce delta endotoxins. Several hybrids available, and some may contain second generation European corn borer different promoters are available and the both corn borer and corn rootworm is expected to be substantially better than choice of promoter also affects where and events. The available events are generally would be expected from a single how much delta endotoxin is produced in summarized in Table 1. well timed insecticide treatment. Q: Are there other advantages Q: I have experienced failures of Q: Are there other disadvantages to using Bt corn instead of an rootworm insecticides. Are the to using Bt corn compared to insecticide to control corn borers? rootworm events more reliable than conventional pest management A: Bt corn will control corn borers insecticides? practices? without directly affecting predators and A: This is a difficult comparison to make. A: There may be difficulty in marketing other beneficial insects. This should make Conventional insecticide application Bt corn destined for international markets. management of other pests such as failures have been reported many times, The international marketing situation mites easier, although there are no field but few of these have been associated changes rapidly, so it is impossible to data to support this claim. with genetic resistance in rootworm know how the rules might change between populations. Rootworm control failures hybrid selection and harvest. This is Q: Are there disadvantages to using with one event have been documented and most commonly a problem with newly Bt corn compared to conventional could spread to include other rootworm approved events. corn borer control? events. These failures are due to genetic adaptation by the rootworm. The cause of Q: What will be the additional cost A: There will be an additional cost to Bt other event failures is unknown. corn seed regardless of whether there for Bt corn seed? is an economic corn borer infestation. A: It should cost from $5 (dry land) to $10 Conventional chemical control allows you Q: What about the other corn pests I (irrigated) per acre to use a given Bt corn to wait and see if an infestation develops have to deal with every year? event, depending on seeding rates. There before investing in insect management. A: Events targeting corn rootworms, corn may be additional costs for other traits. In Also, compliance with refuge requirements borers, western bean cutworm, and several some hybrids, one or both of the Bt traits (see below) may complicate planting, other caterpillar species are available. No may be available only in combination harvest and pest management activities. events are available for spider mites. (stacked traits) with other traits such as herbicide resistance. Q: What kind of corn rootworm Q: Can I plant Bt corn and forget control can I expect from Bt corn? about insects and mites? Q: Where should I use Bt corn in my A: Most university studies have shown A: No, Bt corn will not let you forget operation? corn rootworm control with Bt events to completely about insect pests. Scouting A: Bt corn should be used only where be superior to soil insecticides and seed and management will still be necessary the risk of infestation by a targeted pest is treatments except under conditions of very for some pests. Table 2 shows the major high. high corn rootworm pressure. Under such corn pests and the expected effect of conditions performance with older events commercially available events. Also, is more similar to that of soil-applied pests in refuge acres need to be managed insecticides, while remaining superior to conventionally. seed treatments. However, newer events and event combinations tend to maintain a Table 2. Major corn pests and the expected effect with Bt corn. performance advantage over conventional Corn Pest Effect of Bt Corn Comments treatments. Armyworm Variable Data lacking. Corn rootworm adults No control Q: Are there other advantages Corn rootworm larvae Control Only with corn rootworm specific events. Field to using Bt corn instead of resistance reported for events containing an insecticide to control corn Cry3Bb1. rootworms? Corn leaf aphid No control Less insecticide use may reduce aphid activity. A: Bt corn would eliminate the need for Corn earworm Control Control with Cry1F and VIP3Aa20. the specialized equipment needed to apply Cutworms Variable Cry1F and VIP3Aa20 events effective against soil insecticides and the need to handle black cutworm. Data lacking on other species. these chemicals. European corn borer Control No control with single events targeting corn rootworm or VIP3Aa20. Fall armyworm Variable Cry1F and VIP3Aa20 events more effective. Q: Are there disadvantages to using Bt corn compared to conventional Grasshoppers No control corn rootworm control? Southwestern corn borer Control No control with single events targeting corn rootworm. A: Compliance with refuge requirements Spider mites No control Less insecticide use may reduce mite activity. (see below) may complicate planting, harvest and pest management activities. Western bean cutworm Variable Cry1F and VIP3Aa20 events effective. Wireworms No control Q: Where are the high risk areas for flights typically extend over long periods seed premiums. Use this seed in situations European corn borer? of time. Economic infestations from with higher pest risk (with European corn A: Colorado State University Extension either generation are likely and often both borer, for example, in the earliest and latest entomologists recognize the following generations need treatment in the same planted fields). European corn borer risk areas within field. It’s often difficult to obtain adequate the Golden Plains area (Kit Carson, second generation control with a single Q: Will corn borers or corn Phillips, Washington and Yuma counties) insecticide application. The use of Bt corn rootworms eventually overcome based on more than a decade of pest hybrids are recommended for this area, the delta endotoxins produced by survey information. Pest survey data are regardless of planting date or maturity. Bt corn, as has been observed with insufficient to characterize European corn greenbug resistance in sorghum borer risk for other parts of the state. Q: If I am not in one of these risk hybrids or with many insects and Zone 1 (Burlington, Bonny Dam, areas, how can I to justify switching various insecticides? Kirk) is characterized by heavy soils and to Bt corn to control corn borers? A: Insects can develop resistance to Bt consistently low insect light trap catches. A: Take a look at your average toxins. Resistance in diamondback moth Areas in this zone generally are not expenditures for insect management and other vegetable pests to commercial expected to have economic European (scouting, insecticides and application) Bt insecticides has developed in several corn borer infestations, although growers and your average losses to corn borers parts of the world. This is also a major in the Kirk area experience occasional over the last five years. Your annual total concern for all Bt modified crops because problems. Growers in Zone 1 should select of corn borer management costs and crop they put so much selective pressure on well adapted non Bt corn hybrids, scout for value lost should be similar to the cost the pest. However, apart from western insect pest problems and apply appropriate of switching to a Bt corn event targeting corn rootworm, no cases of resistance in insecticides if justified. The exception might corn borer. any targeted corn or cotton pests have be the Kirk area because it has a long (four been documented since 1996 when Bt to five week) second generation flight in crops first were grown extensively in the Q: Where are the high risk areas for some years, increasing the probability that United States. late planted or late maturing varieties will corn rootworm? experience economic infestation. Bt corn A: Corn rootworm risk is considered Q: What is being done to avoid corn hybrids might be an appropriate choice for high only in continuous corn. However, borer resistance to Bt corn? these situations. continuous corn grown on sandy soils is Zone 2 (Yuma, Clarkville, Holyoke) considered a lower risk. A: University researchers, the seed has a high probability of late planting industry, and the EPA are working or late maturing varieties due to heavy together to develop resistance Q: How can I justify switching to Bt soils. These areas also have a consistent management plans that are effective and corn for corn rootworm control? history of a prolonged second generation practical. They are based on the high dose flight that result in economic infestations. A: If you currently use a soil insecticide or and the refuge strategies. The Bt trait would be an appropriate control adult corn rootworms to prevent choice for late planted or late maturing egg laying, you are likely justified in using Q: What is the high dose strategy? hybrids in these areas. The prolonged Bt corn for corn rootworm control. flight makes treatment decisions difficult. A: The idea is to use Bt corn hybrids that produce enough delta endotoxin to The infestations accumulated over the Q: Should I plant all of my corn kill even partially resistant corn borers. season are economically significant, but acreage to Bt corn? not enough of the infestation occurs in Killing partially resistant corn borers and any two week period to justify the use of A: No! The EPA has published guidelines preventing their mating greatly delays an insecticide. The first generation flight on resistance management (refuge the development of resistance. High dose is consistent enough in these areas that strategy) that affect how much you can events currently are not available for corn Bt hybrids might be considered for early plant. Details on these guidelines are in the rootworms. planting situations. Although there is not a EPA document Biopesticides Registration Action Document: Bacillus thuringiensis consistent need for Bt hybrids in this zone, Q: How does this strategy affect Plant Incorporated Protectants (www.epa. it will be important to consider resistance producers? management requirements when selecting gov/pesticides/biopesticides/pips/bt_brad. A: hybrids and their acreage allocation. htm). How much to plant also depends on Some events are not as high dose as Zone 3 (Eckley, Wray, Wauneta – the severity and the consistency of your others and some areas are considered to north of Hwy 34 and east of Yuma) is corn borer or corn rootworm problems. be more likely to develop insect resistance characterized by light soils, relatively Your average annual total of management than others. The EPA may prohibit the sale uniform crop maturity, and consistently costs and crop value lost to these insects of certain events in certain regions. In the large first and second generation European over the last five years will give you an past, sales of two events were prohibited in corn borer flights. Also, second generation idea of how much to spend on Bt corn some southeast Colorado counties. Q: What is the refuge strategy? Q: Can I use “refuge in a bag” Acknowledgments: A: If a certain acreage (refuge) is planted hybrid? I would like to thank Gary Hein, with non Bt hybrids then any corn borers A: This concept is just entering the University of Nebraska; Jerry Alldredge, or corn rootworms coming out of these marketplace, but should become more and Assefa Gebre-Amlak, Bruce Bosley, Randy areas will be susceptible to Bt. They will more available over the next few years. Buhler, Pat Byrne, Jerry Johnson, Ron mate with any survivors from the Bt corn In general, hybrids with two or more Meyer, Stan Pilcher, Elaine Roberts, and and preserve the genetic susceptibility of events for both European corn borer and John Shanahan, all of Colorado State the overall population. rootworms will be allowed to use this University; and Phil Sloderbeck, Kansas strategy. State University, Garden City, for reading Q: How does the refuge strategy and commenting on earlier versions. affect producers? Q: What can I, as a grower, do to A: Current EPA policy restricts growers help avoid the development of pests to a certain percentage Bt corn acreage that are resistant to Bt corn? for either corn rootworm or corn borer A: Follow the resistance management control. Hybrids with a single event for recommendations provided by CSU corn borer or for rootworm can be planted Extension specialists, your seed company, on only 80 percent of a grower’s acres. and the EPA. Use good agronomic Dual event hybrids will have a lower practices to avoid unneeded crop stress. refuge requirement. Report any suspected failure s to the seed company and to local Q: Can I plant my refuge in the same Extension entomologists as soon as field as the Bt corn? possible. A: Yes, EPA allows the non Bt corn refuge to be planted as strips running the length Q: How do I tell if I have a Bt corn of the field. The strips need to be at least failure? six to 12 rows wide. A: Identifying resistance to Bt corn is a complicated process. A few damaged Q: How is the refuge strategy for plants in a field may not be a sign that Bt corn hybrids for corn rootworm resistance has developed. For example, control different from the strategy the occasional susceptible plant may get for corn borer hybrids? into a field either from the seed source A: Refuge requirements are becoming or as volunteer plants. If the frequency more complicated as hybrids with different of damaged plants seems unusually high, combinations of events become available. however, it should be reported. Be sure to understand and comply with the requirements for the hybrid(s) that Q: Are there ways to make future you plant. Bt corn hybrids less prone to resistance development? Q: I have heard the term “refuge in a A: Some future hybrids will have bag,” what is this? combinations of different delta endotoxin A: This is the concept of planting a or VIP forms that should have fewer mixture of Bt corn hybrid seed and problems with resistance development. non Bt seed (about 5 percent). This Others may have different genes that allows the grower to comply with refuge produce different toxins, such as requirements without planting or . Hybrids with toxin combinations maintaining a separate refuge. should be less likely to have problems with resistance development in pest insects.

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