A GROWER’SHANDBOOKS E C O N D E D I T I O N

Controlling Corn Insect Pests with Bt Corn Technology

AuthorsEditor:Tracey BauteOntario Ministry of Agriculture and FoodAgronomy Building, Ridgetown CollegeP.O. Box 400Ridgetown, Ontario N0P 2C0Tel: (519) 674-1696Fax: (519) 674-1564E-Mail: tracey.baute@omaf.gov.on.ca

Other Authors:Albert Tenuta (Editor First Edition)Ontario Ministry of Agriculture and FoodAgronomy Building, Ridgetown CollegeP.O. Box 400Ridgetown, Ontario N0P 2C0Tel: (519) 674-1617Fax: (519) 674-1564E-Mail: albert.tenuta@omaf.gov.on.ca

Art SchaafsmaRidgetown College/University of GuelphRidgetown, Ontario N0P 2C0Tel: (519) 674-1624Fax: (519) 674-1600E-Mail: aschaafs@ridgetownc.uoguelph.ca

François MelocheAgriculture and Agri-Food CanadaEastern Cereal & Oilseed Research CentreNeatby Building960 Carling AvenueOttawa, Ontario K1A 0C6Tel: (613) 759-1615Fax: (613) 759-1926E-Mail: melochefc@agr.gc.ca

Marlin E. RiceIowa State UniversityDepartment of Entomology103 Insectary Bldg.Iowa State University Ames IA 50011 Tel: (515) 294-1101 Fax (515) 294-8027E-Mail: merice@iastate.edu

Michèle RoyGouvernement du Québec (MAPAQ)Direction de l'innovation scientifique et technologique Complexe scientifique 2700, rue Einstein Sainte-Foy (Québec) G1P 3W8 Phone: (418) 643-9729Fax: (418) 646-6805E-Mail: michele.roy@agr.gouv.qc.ca

Mark SearsUniversity of GuelphDept. of Environmental BiologyGuelph, Ontario N1G 2W1Tel: (519) 824-4120Fax: (519) 837-0442E-Mail: msears@uoguelph.ca

CitationBaute,T. (ed), 2004. A Grower's Handbook; Controlling Corn Insect Pests with Bt Corn Technology.Second Edition. Canadian Corn Pest Coalition. Ridgetown, Ontario. 24pp.

Printed on Recycled Stock10% Post-Consumer Fiber

AcknowledgementsThe authors would like to thank the following individuals, associations and companies for theircontributions: Henri Goulet (Agriculture and Agri-Food Canada); Elaine Roddy (Ontario Ministry ofAgriculture and Food); Ontario Corn Producers’Association; the Canadian Food Inspection Agency;Agriculture and Agri-Food Canada; Dow AgroSciences Canada; Monsanto Canada; Pioneer Hi-BredLimited; and Syngenta Seeds Canada.

Product brand names mentioned within are registered trademarks of their respective companies.

TABLE OF CONTENTSWho Is the Canadian Corn Pest Coalition? .................................................................................. 4What This Book Is About ............................................................................................................ 4

European Corn Borer and Its Distribution .................................................................................... 5Why Manage European Corn Borer? ............................................................................................ 5European Corn Borer Life Cycle .................................................................................................. 6What Does European Corn Borer Damage Look Like? .................................................................. 7

Corn Rootworm and Its Distribution ............................................................................................ 8 Corn Rootworm Life Cycle .......................................................................................................... 9What Does CRW Damage Look Like? .......................................................................................... 9Best Management Practices for CRW ........................................................................................ 10

What Is Bt Corn? ...................................................................................................................... 11How Does the Bt Gene Work? .................................................................................................. 11What Have We Learned From Bt Corn for ECB? ........................................................................ 13YieldGard Rootworm Bt Corn and YieldGard Plus ...................................................................... 13

The Challenge - Resistance Management .................................................................................. 14How Resistance Develops .......................................................................................................... 14Resistance Development by ECB ................................................................................................ 15Managing ECB Resistance Through "High Dose / Refuge Strategy" ............................................ 15Insect Resistance Management Requirements for ECB Bt Corn .................................................. 16Insect Resistance Management Requirements for ECB Bt Sweet Corn ........................................ 16Insect Resistance Management Requirements for YieldGard Rootworm Bt Corn ........................ 17Insect Resistance Management Requirements for YieldGard Plus Bt Corn .................................. 17Resistance Development by Corn Rootworm .............................................................................. 18Monitoring Your Bt Fields .......................................................................................................... 18

Refuge Planting Options for Bt Corn Technology ........................................................................ 19

What are the Impacts on Natural Enemies and other Non-Target Organisms? ............................ 20What About the Monarch Butterfly? .......................................................................................... 20Glossary of Basic Biotechnology Terms ...................................................................................... 21

A GROWER’SHANDBOOKS E C O N D E D I T I O N

4

Representatives of the seed corn industry, growerassociations, regulatory agencies, academic institutionsand extension and research staff from both provincialand federal governments founded the Canadian CornPest Coalition in 1997. This working group bringstogether industry leaders in corn breeding,entomology, insect resistance management, pathology,agronomy, environmental biology, regulatory scienceand public affairs.

Each member is committed to the common goal ofresponsibly deploying and managing new pestmanagement technologies for corn as they areintroduced in Canada to support their continuedeffectiveness. The main focus of the CCPCcurrently is ongoing proactive post-marketstewardship of Bacillus thuringiensis (Bt) corn hybrid technologyfor European corn borer (ECB) control. The group has recently turned its attention to include thedevelopment of similar strategies for Bt-based corn rootworm (CRW) control. The strategy to accomplish both its initialmandate and future initiatives includes co-operative scientific investigation and successful grower education to promoteindividual accountability for trait stewardship at all levels of the production chain.

This is the second edition of "A Grower'sHandbook" produced by the CCPC. Thiscurrent edition includes new information oncorn rootworm biology and the new Bt cornevents registered in Canada. It also includes indepth information on insect resistancemanagement strategies for both ECB Bt cornand CRW Bt corn.

This book is only part of the proactive approachtaken by the CCPC to best inform growers oncorn pest management and transgenictechnology. For further information on variouscorn pest issues, visit the Canadian Corn PestCoalition website at:

Who Is the Canadian Corn Pest Coalition?

w w w . c o r n p e s t . c a

A Grower’sHandbookControlling European

Corn Borer with

Bt Corn Technology

How to get the most from Bt Corn!

• Use Bt corn in fields at economic risk of corn borer damage

• Keep accurate records of where Bt and non-Bt hybrids

are planted

• Initiate an Insect Resistant Management Plan (IRM):

- Plant at least 20% non-Bt corn

- Keep all Bt corn within 400 metres (quarter mile)

of non-Bt corn

• Scout for potential resistant corn borers

A GROWER’SHANDBOOKS E C O N D E D I T I O N

Controlling Corn Insect Pests with Bt Corn Technology

What This Book Is About

5

The European corn borer (ECB), Ostrinia nubilalis, is the most destructive insectpest of field, seed and sweet corn in Canada. ECB was introduced into NorthAmerica in 1910 from a central European broom factory. It was first reported inOntario in 1920, 1925 in New Brunswick, 1926 in Quebec, 1929 in Nova Scotia, 1948 in Manitoba,

1949 in Saskatchewan and 1956 in Alberta (waseradicated but re-appeared in 1980).

In Canada, the European corn borer isdistributed from the southern

portions of the Prairieprovinces to theMaritimes, generallywhere corn is grown.ECB is a moth larva

that bores into the stalkand ears of corn and other

host plants.

Most areas of Canada have a strain thatundergoes a single generation per year

(univoltine), whereas southwestern Ontarioand southern Quebec (along the St.Lawrence River) have the two-generationper year strain (bivoltine). Damage severity

varies from year to year, depending on thepopulation of the insect. The introduction of Btcorn has aided producers in better managingthis destructive pest.

Number of ECBGenerations

1234

European Corn Borer and Its Distribution

Canadian corn producers lose millions of dollars annuallyto corn borer as a result of lost yield, increased harvest timeand reduced grain quality due to disease. Although yieldloss estimates are difficult to determine, some studies haveshown that one corn borer could reduce yield by 3 to 5 %,and greater reductions can be expected under high cornborer pressure. (Table 1)

OTHER FACTORS THAT CAN INFLUENCE YIELDLOSS DUE TO CORN BORER INCLUDE:

• level of hybrid tolerance or resistance to the borer

• climatic conditions experienced (drought, heat etc.)

• the plant stage attacked.

Why Manage European Corn Borer?

Plant Stage1 2 3

Early Whorl 5.5 8.2 10.0

Late Whorl 4.4 6.6 8.1

Pre-tassel 6.6 9.9 12.1

Pollen Shed 4.4 6.6 8.1

Blister Stage 3.0 4.5 5.5

Dough Stage 2.0 3.0 3.7

Number of Corn Borer per Plant(Estimated % Yield Loss)

TABLE 1

6

European Corn Borer Life CycleThe corn borer undergoes four stages: egg, larva, pupa and adult for eachgeneration. Corn damage is caused solely by the larval stages. Within the larvalstage, there are five molting stages called instars. The earliest instars feed on theleaves of the plants while the later instars tunnel into the plant.The Europeancorn borer overwinters as a full grown larva in corn (stalks and cob residues,weeds and others). Within the stalk a larva will transform into a pupa and thenemerge as a moth. In the one generation per year area, adult moths emerge frommid June to August. In the two generation area, moths of the first generationemerge from late May to July and those of the second generation emerge fromlate July to early September. In hot years, an additional partial third generationmay develop in October. This is often referred to as a "suicide" generation sincemost of the larvae will not develop sufficiently to survive the winter.

Egg Mass

Newly hatching egg mass

2nd-3rd instar larva

4th-5th instar larva

Pupa

Adults

NOV. - APR. MAY JUNE JULY AUGUST SEPT. OCT.ONE GENERATION STRAIN (UNIVOLTINE) LIFE CYCLE

NOV. - APR. MAY JUNE JULY AUGUST SEPT. OCT.

First GenerationSecond Generation

First GenerationSecond Generation

TWO GENERATION STRAIN (BIVOLTINE) LIFE CYCLE

7

What Does Corn Borer Damage Look Like?

Window-pane effect - smallcircular feeding areas on theleaf where the first instarlarvae did not feed all the waythrough but left a thin layerof leaf tissue (a)

FIRST GENERATION CORN BORER DAMAGE

SECOND GENERATION CORN BORER DAMAGE

a

Lodging - lodged plants (f)may also increase as a resultof weakened stalks, andincreased disease.

f

Shot-gun effect - as thelarvae develop, the size of theholes in the leaves get largerand the first and second instarlarvae are able to feedcompletely through the leaf(b). Feeding pattern becomesrather apparent when thecorn leaves extend out of theplant whorl (c).

b

c

• Considered to be the most damaging to corn.

• Pay particular attention to late-planted fieldsor fields that are pollinating since these fieldsare the most attractive to the adult moths.

• Damage includes leaf feeding, stalk tunneling(g), grain feeding (h), ear drop, tassel breakage(i) and shank tunneling (j).

• Stalk and ear rot diseases (g) also tend to bemore prevalent in areas infested by secondgeneration ECB.

g

h

i

j

Tunneling - points of entryof the third and fourth instarsoften have excrement or"frass" around them (d).Larva will enter through themidrib or at the base of theleaf axil to pupate or willform a cocoon on the leavesor tassel. This can result insignificant physiological yieldloss by interfering with thetransportation of nutrientsand water to the stalk andleaves (e).

d

e

8

Corn rootworm (CRW) is the most destructive insect pest of corn in NorthAmerica. There are two species of corn rootworm found in the corn growingregions of Canada; the western (Diabrotica virgifera virgifera) (WCR) and thenorthern (D. barberi) (NCR) corn rootworm. Both the adult and larval stages ofthis insect can feed on corn.

Adult WCR beetles are approx. 6mm in length and vary in colour from lightyellow to green. The females typically have three wavy black stripes on theirwing covers while the three stripes on males are fused and are undifferentiated.Male WCR adults are also slightly smaller, and their antenna are longer than thefemales. WCR may be confused with striped cucumber beetles, which also havesimilar colouring and striping; however the stripes on the cucumber beetle arestraight with well defined margins. Also, the striped cucumber beetle'sabdomen is black on the underside compared to WCR which is not. TheNCR adult beetle is also approx. 6 mm long and has beige to dark green wingcovers (elytra), with no particular markings that differentiate between malesand females.

The immature stage (larva) of this insect is whitish in colour, measuring 2 to 10mm long with a brown head and brown anal plate. Though adults can feed oncorn silks and pollen, it is the larval stage that causes the most economic injuryin corn.

Corn Rootworm and Its Distribution

Western Corn Rootworm adult

Northern Corn Rootworm adult

Rootworm larva

DISTRIBUTION IN CANADA

WesternCorn Rootworm

NorthernCorn Rootworm

The distribution of WCR and NCR overlap. NCR is present in Ontario, Quebec and the Atlantic provinces whilethe WCR is found throughout Ontario and west of Quebec City. In southwestern Ontario,WCR predominatewith a ratio of greater than 4:1 WCR to NCR whereas in eastern Ontario and Quebec, the ratio is opposite with8:1 NCR to WCR.

9

Both CRW species have one

generation per year and overwinter

in the soil as eggs. Corn rootworms

undergo four developmental stages:

egg, larva, pupa, adult. Egg hatch

occurs around mid-June. The larvae

undergo three larval growth periods.

Third instars construct an earthen soil

cocoon and transform into an inactive

pupa. The pupa then matures into an

adult and emergence occurs between

late-July and the end of September.

Males emerge first and need this extra

time to complete sexual development.

During that period, males are

searching for females to mate. After

mating, the female deposits the first

egg clutch 11-16 days later. Females

continue feeding to mature more eggs

and another egg clutch is deposited.

This process of female feeding, egg

maturation and oviposition is repeated

until all eggs have been laid. Female

WCR may lay more than 1000 eggs

and NCR approximately 300 eggs.

Most of the eggs are deposited during

August with the majority of the eggs

laid in the top 30 cm of soil.

CRW adults are typically attracted to

corn fields for egg laying. Conse-

quently, the majority of the first eggs

are laid in the same field from which

the beetles emerged. However, some

may migrate to other corn fields that

are shedding pollen to lay more eggs.

Fields in flower are the most attractive

because of the strong scent the corn

releases during pollination. Therefore,

the latest flowering corn fields are at

a greater risk of being infested.

Adults prefer fine textured soils such

as loams and clays, so they can use soil

cracks and earthworm burrows to

deposit eggs where soil moisture is

adequate. Eggs also require adequate

moisture in the spring to hatch.

Sandy soils tend to be less prone to

CRW injury because sand is abrasive

to the eggs and does not retain

moisture.

Once corn rootworm eggs hatch in lateMay-early June, the first instar larvaeare attracted to the CO2 and othermolecules released by corn roots. These larvae can travel 1 m to reachthe corn root. Young larvae initially will feed on root hairs. Certainsugars exuded by the root stimulate larval feeding. Larvae then tunnelinto the cortex region of the primary roots from nodes 1-3, causingroot scarring. As the corn plant continues to grow and CRW larvaereach the 2nd and 3rd growth stages, they begin feeding on root tipsof nodes 4-6. Corn roots typically average 7-8 nodes of roots.Rootworm feeding destroys the growing point at the tips of the roots

and stops root elongation. Larvae that continue to feed can prune the root back to the base of the root (a). Root feedingcontinues until the larvae reach the pupation stage (late July). Peak root feeding, i.e., when larvae are causing the greatest

a

What Does CRW Damage Look Like?

NOV. - APR. MAY JUNE JULY AUGUST SEPT. OCT.

Corn Rootworm Life Cycle

10

amount of damage, occurs during the first two weeks of July and coincides withcorn tasselling. Root pruning, environmental conditions (e.g. wet soils, high winds),herbicide injury and soil compaction (hinders root growth) may cause lodging or increase the risk of lodging (c). Also, severe root feeding may occur without evidenceof lodging. Finally, some hybrids have stronger root systems or roots that regeneratemore rapidly and may be less likely to lodge under higher levels of damage.

Adults that emerge in early July feed oncorn leaves and then move to ear silkand pollen as it appears. They can prunethe silks back to the ear tip interferingwith pollination (b). Severe clippingdamage on very late plants may causebarren ears. This is rare since silk andpollen shedding in a field are spread overtime and this favours adult dispersionthroughout the field. Adult leaf feedingdoes not cause much yield loss, but maycreate an avenue for invading pathogensto enter and cause various leaf diseases.

Best Management Practices for CRWBecause CRW generally lay their eggsin corn fields and the larvae needcorn to develop, rotation to a non-corn crop remains the most effectiveand economical control strategy inCanada. Monitoring for damage infirst year corn should still beconducted.

In some cases, when corn is plantedin the year following corn, someprotection may be necessary. Thethree control options for protectionare: YieldGard Bt corn for cornrootworm, seed treatment withPoncho™ (clothianidin) at the highrate or an application of either Force®

(tefluthrin) or Counter (terbufos)granular insecticides at planting. Allof these methods are preventivemeasures that assume an infestationabove an economic threshold.

In some areas of the US corn beltwhere vast areas of corn are rotated

with soybean in a two crop rotation,beetles of the WCR have adapted tolaying eggs in non-corn fields (i.esoybeans, wheat, oats, etc.). Thisphenomenon has not beendocumented in Canada to date but afew first year corn fields in Ontariohave experienced lodging and rootpruning due to rootworm larvae.Further research is being conductedto verify whether this is due to therotation variant or because ofenvironmental conditions favouringegg laying outside of corn fields.

In general, the odds of an economicinfestation are less than one in five,but it is difficult to determine whichfield is at risk. Fields not at risk canbe eliminated by scouting the cornonce per week in August to count thenumber of adults present at the earzone (i.e. one leaf below to one leafabove the ear node). If the total adult

count is on average less than onewestern corn rootworm (or twonorthern corn rootworm) adults perplant in August, then the field willnot need a control measure thefollowing spring.

What Does CRW Damage Look Like? (cont’d)

b

c

11

FOR DETAILED INFORMATION REFER TO THE INFOSHEET TITLED "HOW IS BT PUT INTO A CORN PLANT" AVAILABLE AT WWW.CORNPEST.CA

The Bt proteins produced in these corn products are quite specific and lethal tothe juvenile stage (larva) of a few members of one of two specific groups ofinsects; Lepidoptera (moths and butterflies) and Coleoptera (beetles). The larvamust ingest plant tissue that contains the Bt protein for it to work. As the larvafeeds, the insect's own digestive enzymes activate the toxic form of the protein.The toxin binds to specific receptors on the cells in the lining of the larva's gut,and ruptures these cells. These receptors are specific to the Bt Cry proteinstructure and must be present for the Bt protein to work. The larva has analkaline environment in the gut, which is also critical to activate the toxin.Within hours, the larva stops feeding and its stomach lining ruptures. Bacteriafrom the gut invade the body cavity and the larva becomes infected and dieswithin 24 to 48 hours.Animals and humans have acidic digestive systems andlack the receptor cells which the protein requires for binding, so the proteinposes no risk to these groups and is digested like any other protein.

How Does the Bt Gene Work?

Promoter turns on production of Bt protein in corn plant

•Larva ingests corn tissue

containing Bt protein•

Larva’s digestive enzymesactivate toxin

•Toxins bind to specific receptors

in gut lining of larva•

Cells rupture and leak in gut•

Larva stops feeding•

Larva (insect) dies

Btcornis oneof thefirstexamples ofagriculturalbiotechnology thathas a practical on-farmapplication. Biotechnology includesprocesses by which the genetic codeor DNA from one organism is placedinto another organism. Plants thatreceive these genes are called"transgenic plants". These genes arechosen because they produce productsthat provide or enhance certain traits(e.g., insect, disease or herbicideresistance) or quality (e.g., increasedoil or amino acids) of the crop.

Three primary components of theinserted genetic package are:

Bt protein gene - expressesspecific desired Cry (crystal)

protein

Promoter - controls where and howmuch of the Cry protein a plantproduces (eg. leaves, green tissueand pollen only vs. throughout theplant including the ear)

Genetic marker -- used to identifysuccessful transformations (eg.herbicide tolerance)

In the case of Bt corn, the transgeniccorn plant is modified to produce aninsecticidal protein that occursnaturally in Bacillus thuringiensis(Bt). This bacterium is commonlyfound in soils throughout the world.There are several strains of Bt andeach produces different insecticidalproteins, in the form of crystals ("Cry

proteins"), which control specificgroups of insect pests (Table 2, nextpage). Most of the Bt corn hybridsmarketed in Canada are targetedeither against the European cornborer (Cry1Ab, Cry1F protein) orthe corn rootworm (currently onlyCry3Bb protein).

The Cry proteins produced by Bt are"environmentally safe" materials. TheCry 1Ab protein has been used as afoliar insecticide by organic growersand foresters since the 30s. TheseCry proteins and their breakdowncomponents are non toxic tovertebrates, including humans. Thebuilt-in delivery system protects theprotein from environmental factorsthat can influence the effectiveness oftypical foliar insecticide applications.Bt corn reduces the potential forsynthetic pesticide usage, therebylowering environmental and humanhealth concerns.

What Is Bt Corn?

12

CURRENTLY REGISTERED TRANSGENIC CORN PRODUCTS (CANADA)TABLE 2

STRAIN OF Bacillusthuringinsis

CryProtein

TargetPests Event Brand Name Company Expressed In

* NatureGard (Event 176) licensed to Hyland, Pride and others

** YieldGard (MON810) licensed to Cooperative Federée de Québec, DEKALB, Dow AgroSciences/Mycogen Seeds, Garst, Hyland, Maizex, Pickseed, Pioneer Hi-Bred, Pride and others

+ May not provide complete protection against second generation ECB. Does not protect against ECB damage to the ear.++ May control young larvae only

Bt var. kurstaki(controls certaincaterpillars)

Bt var. aizawai(controls certaincaterpillars)

Bt var. israelensis(controls flies andmosquito larvae)

Bt var. tolworthi(controls certaincaterpillars)

Bt var. SanDiego(tenebrionis)(controls certainbeetle larvae)

Cry1AbEuropean

Corn Borer176+ Knockout Syngenta Seeds

Green Tissue andpollen only

Cry1AbEuropean

Corn BorerBT11 YieldGard Syngenta Seeds All plant parts

Cry1AbEuropean

Corn BorerMON810 YieldGard** Monsanto All plant parts

Cry1AcEuropean

Corn BorerDBT418 Bt-Extra

No LongerRegistered

Cry1Aa

DiamondbackMoth,

Cabbage Looper, Fall Armyworm

Not Applicable

Cry1F

EuropeanCorn Borer,

Black Cutworm++

Fall Armyworm

TC1507 Herculex IDow AgroSciences/

Pioneer Hi-BredAll plant parts

Cry1AbEuropean

Corn Borer176+ NatureGard*

Dow AgroSciences/Mycogen Seeds

Green Tissue andpollen only

Cry3Bb1Corn

RootwormMON863

YieldGardRootworm

MonsantoAll tissue

including roots

Cry9CEuropean

Corn BorerCHB351 Starlink

Was not grantedapproval in Canada

Cry3CColorado

Potato BeetleNot Applicable

Cry4Mosquitoes &

Black FliesNot Applicable

Cry3AColorado

Potato BeetleNot Applicable

13

YieldGard Rootworm corn utilizes adifferent Bt protein that controlsdifferent insects than Bt corn for cornborer control. YieldGard Rootwormexpresses the Cry3Bb1 protein in theplant, protecting the plant against root

feeding fromthe

western and northern corn rootwormlarvae. This product will not provideprotection against the adult cornrootworm or from ECB larvae.

YieldGard Plus is the newest productavailable which expresses both theCry1Ab and Cry3Bb1 proteins,providing protection against feeding

from both ECB larvae and thewestern and northern corn rootwormlarvae. Appropriate resistancemanagement strategies have beencreated for both YieldGardRootworm and YieldGard Plus toensure the longevity of these twonew management tools.

Bt HYBRIDS DO NOT GUARANTEEHIGHEST YIELDSome high performance conventional corn hybridsperformed as well as or better than the Bt hybrids,especially under low to moderate European corn borerpressure.

Bt GENE PROVIDES "YIELD PROTECTION"AGAINST CORN BORER, NOT "YIELDINCREASES"Yield potential is determined by the hybrid’s genetic makeup and can be influenced by many variables other thancorn borer. These can be weather related (drought, heat,cold, flooding, light quality, etc) and agronomic factors(plant populations, fertilization, seed bed, seeding depth,weed control, row width, tillage, compaction, etc.). The Btgene technology is rapidly being incorporated into manyof the top performing corn hybrids. Although thistechnology will not increase a hybrid's yield potential itwill optimize the hybrid's performance through improvedplant health while reducing corn borer impact on yieldand reducing stalk and ear rot incidence.

ALL Bt EVENTS DO NOT PROVIDE EQUALEUROPEAN CORN BORER PROTECTIONAll events (BT11, MON810, 176 and TC1507) providegood early corn borer protection (first generation) and allcould be used in early planted fields.

Event 176 expresses Bt protein in leaf tissue and providesexcellent European corn borer protection for most of theseason but Bt levels will diminish as the corn plantmatures.This reduction in Bt levels late in the season offersless protection against the 2nd generation of corn borer

and can result in increased plant breakage due tostalk tunneling. Event 176 hybrids offerless protection against ear damage,which can lead to greater risk of earmolds.

In late-planted corn, this late damage hasminimal effect on yield since yield is alreadyset. Events BT11, MON810 and TC1507 provide seasonlong protection and the Bt protein is expressed in all theplant tissue and the grain.

Bt ANOTHER "TOOL" IN FIGHT AGAINSTCORN BORERBt will not eliminate European corn borer on its own,and therefore an integrated approach to pest management(IPM) should be implemented.

HYBRID SELECTION IS CRUCIALMost commercially available non-Bt hybrids have beenselected for good standability and good native corn borertolerance. The Bt gene or any other single gene will notmake an average hybrid a "bin buster". The gene for theBt protein is only one of several thousand that make up acorn plant. Focus on the total genetic package and chooseagronomic characteristics that are suitable for your farm.This will provide you with the greatest genetic yieldpotential. Hybrid selection is still one of the most crucialdecisions you can make. Since European corn borerpopulations fluctuate, it is best to select hybrids based onperformance over several years and target Bt corn varietiesto high risk fields.

What Have We Learned About Bt Corn for ECB?

YieldGard Rootworm Bt Corn and YieldGard Plus

14

Bt corn hybrids have beencommercially available in Canadasince 1997 and have become avaluable tool in controlling Europeancorn borer. In 2003, Bt corn hybridsspecific for the control of cornrootworm larvae also becamecommercially available. Scientistsacross North America in public andprivate sectors agree that these twopests could develop resistance to the

Bt under conditions of continued use.To prevent or delay the onset ofresistance, the CanadianFood Inspection Agency(CFIA) requires that eachregistrant of Bt cornimplement an insect resistancemanagement (IRM) strategy withproducers. Proper implementation ofthe IRM plan will be critical to thesustainability of this technology. If

you areplanning to

plant Bt corn thisyear, you will need to implementan IRM plan.

RESISTANCE COULD OCCUR:

• Because the protein cannot bind to the specific site of the gut wall;

• Some factor in the gut breaks the protein down; or

• Some other factor changes how the insect might respond to the protein. An individual insect cannot "decide" tobecome resistant. Resistance arises within populations through natural genetic variability and increased selection pressureby continual exposure to Bt protein.

There are numerous and repeated examples of poor stewardship of new insect control tools that have resulted in pestresistance and loss of that management technology. We have taken a proactive approach by implementing an InsectResistance Management (IRM) strategy to maximize the effective duration of these lines of Bt corn.

How Resistance Develops

Control becomes ineffective ashigher percentage of moths becomeresistant

C. Prevalent Use of Bt Corn

Incidence of resistant moths (rr) increases with their selective advan-tage for survival and reproduction

B. Introduction of Bt Corn

Resistant Moths (rr)

A. Bt Corn Not Yet Available

Very few moths have genes (rr) that allow larvae to survive on Bt Corn

Susceptible Moths (ss) D. Bartels and W. Hutchinson

The Challenge - Resistance Management

15

In any population of European cornborers, a few of the borers will havetwo copies of genes for resistance (rr),some will have one copy of the gene(rs) and most will have none (ss).Resistance genes are believed to berare. In Bt corn, European corn borerwith one or more copies of resistancegenes (rr or rs) could perhaps surviveand produce more offspring.Improved survival or reproductivesuccess results in a "selectiveadvantage." As the Bt corn acreageincreases, and with it the proportionof the European corn borerpopulation exposed to Bt corn, morelarvae carrying resistance genes couldsurvive to adulthood. The overallpopulation of Bt-resistant individualscould increase with each generation.At some point, control failure couldoccur with resistant larvae reachinginfestation levels in Bt corn fieldssimilar to levels found in non-Bt

corn fields, hence the necessity ofimplementing IRM on your farm andkeeping good records.

The greater the proportion andduration of exposure of corn borerpopulations to the protein, the faster

the selection process occurs. If allcorn acreage in North America wereplanted to Bt corn, the selectionpressure would be extreme andresistance could develop quickly(some estimate within 3-5 years).

Resistance Development by ECB

The North American corn industry has adopted what is called the ‘‘high dose/refuge strategy’’ to manage corn borerresistance to Bt technology. The high-dose/refuge strategy involves exposing one portion of the pest population to Btplants with an extremely high concentration (dose) of the Btprotein, while maintaining another part of the population as arefuge where the pests do not encounter any Bt protein.

THE HIGH DOSE STRATEGY: Plant geneticists designed Bt corn to produce very high levels of Bt Cry proteins, much higher than levels than found on corntreated with Bt insecticides. The intent is to kill all Europeancorn borer larvae with no genes for resistance (ss), plus thosewith one copy of a resistance gene (rs).

Bt protein concentrations in a hybrid vary depending on whichgenetic event was used in its production. The level of Europeancorn borer control against late-season European corn borerinfestations differs between events.

Managing ECB Resistance Through "High Dose / Refuge Strategy"

Mixing of resistant survivors from Bt Corn, with susceptible moths from refuges delays resistance.

Resistant MothsSusceptible Moths

Bt Corn Non-Bt Corn

R. Hellmich

• ECB Bt hybrids may be sold for commercial sweet corn production only (minimum purchase of one

unit of seed, approximately 4.5 acres.)

• Bt hybrids should be planted in large blocks and kept separate from non-Bt hybrid types.

• The grower will not repackage or resell Bt sweet corn hybrids.

• The grower will scout for non-target pests and use IPM strategies. Chemical pesticides may be

applied, if necessary, to prevent economic loss.

• Do not spray Bt microbial pesticides on Bt sweet corn hybrids.

• The grower must destroy any Bt sweet corn stalks that remain in the fields following harvest. This

activity must take place either immediately following harvest or a short period of time (maximum

1 month) later in accordance with local production practices.

• A refuge is not required for sweet corn if these management steps are followed

Insect Resistance Management Requirementsfor ECB Bt Sweet Corn:

• Minimum of 20% of total corn acreage planted to non Bt refuge

• Refuge must be planted within 400 metres (1/4 mile) of the ECB Bt planting(s);

• Do not mix ECB Bt and non-Bt seed at planting because it increases the chance of resistance;

• The use of ECB insecticides is not permitted in the refuge planting;

• Refuge and ECB Bt corn hybrid must be of similar maturity (within 100-150 CHU) to be equally

attractive to the adult moths

• Keep accurate records of corn field planting(s)

Insect Resistance Management Requirementsfor ECB Bt corn:

• For YieldGard Plus Bt corn (containing both ECB and CRW controlling proteins), follow the same

insect resistant management requirements as YieldGard Rootworm corn (directly above). Refuge

must be adjacent to or within YieldGard Plus corn field.

Insect Resistance Management Requirementsfor YieldGard Plus Bt Corn:

• Minimum of 20% of total corn acreage planted to non Bt refuge

• Refuge must be adjacent to or within YieldGard Rootworm corn field;

• Refuge may be treated for CRW larval control with soil-applied insecticides if economic thresholds

prescribe it. Insecticide use for adult control is not permitted;

• YieldGard Rootworm and refuge must be owned or managed by same grower;

• If refuge is treated for other late-season insect pests such as corn borer, then YieldGard Rootworm

field must also be similarly treated ;

• If the adjacent field option is used, YieldGard Rootworm and refuge fields should have the same

crop rotation histories and maturities;

• Mixing CRW Bt and non-Bt corn seed at planting is not permitted

Insect Resistance Management Requirementsfor YieldGard Rootworm Bt Corn:

18

The level of understanding ofresistance development in CRW islow compared with that of ECB,however many studies are underway.Several factors still need to beinvestigated. There are a few keydifferences between the two insects intheir exposure to resistance selection.CRW have two life stages exposed toBt; larva and adult. Also, the dose thatCRW is exposed to is low tomoderate for the Cry3Bb events, asopposed to high dose in the ECB Btevents. Though YieldGardRootworm hybrids are effective atprotecting the roots from larval injury,some adult emergence will take placefrom these Bt fields. Anotherbiological difference is that CRWmate in the same field as they emerge,reducing the chance of geneticmixing from nearby non Bt fields.

For these reasons, entomologists recommend a proactive approach to resistance management for the time being. Thecurrent requirement for refuge size and configuration for YieldGard Rootworm and YieldGard Plus takes into accountwhat growers are already accustomed to for ECB refuge. However, the CRW refuge must be placed within or adjacent tothe YieldGard Rootworm or YieldGard Plus field to accommodate the limited movement of CRW adults at mating.

Resistance Development by Corn Rootworm

Keep careful and accurate records asto where Bt and non-Bt corn wasplanted for both insect monitoringand hybrid performance evaluationpurposes.

Scout for insects and diseases in bothyour Bt and non-Bt fields. Bt cornhybrids are not resistant or tolerant toother diseases and corn insect pestssuch as wireworm, white grubs,seedcorn maggot, seedcorn beetle,flea beetles, aphids, or mites.

Monitor for resistance to Bt corn. Iffeeding damage is detected, investigate

the cause. Verify from field recordsthat a Bt hybrid was planted wherethe injury was found. If needed, gethelp to accurately identify thefeeding pest. Notify seed companyrepresentatives immediately if yoususpect a problem. Seed companieshave diagnostic tests available todetermine if resistance has developedin your field.

For more information on how toaccurately scout for ECB and CRW,visit the Canadian Corn PestCoalition Website at:www.cornpest.ca

Monitoring Your Bt Fields

19

Since both the value of Bt technology and the threat of resistance are real, producers need to consider the following pointson how to best implement an IRM plan on their own farm.

Not all fields are alike so there are various refuge configurations you can follow. Whichever you choose, it is important toensure that your refuge is planted at the same time as your Bt fields, and that you select refuge hybrids that are similar inmaturity (within 100-150 CHU), disease resistance, herbicide tolerance, standability and other traits as your Bt hybrids.This will work to your advantage during weed control and at harvest time, as well as ensure that the moths are attractedequally to both your non-Bt and Bt fields.

Refuge Planting Options for Bt Corn Technology

WHOLE/SEPARATE FIELD

Planting whole field refuge of non-Bthybrids is the simplest and mostpractical option because emptyingseed boxes and switching hybrids isminimized. However, these wholefields must represent a minimum of20 percent of your own total cornacreage. For ECB Bt corn, the refugemust be positioned within 400 metres(quarter-mile) from any of your ownBt corn. For YieldGard RootwormBt corn or YieldGard Plus, the refugemust be adjacent to or within theYieldGard rootworm or YieldGardPlus corn field.

BLOCKS

Many field sizes and configurationswill make the ‘whole field’ optionimpossible and require that a specificblock or portion of a field be plantedas non-Bt refuge. This could result inthe most effective refuge. Onepotential problem in this arrangement

is the possibility of having a non-Bthybrid "land locked" by the main Bthybrid of the field at harvest.

STRIPS

Planting alternating strips of Bt andnon-Bt hybrids can be an effectiverefuge. This approach will eliminatethe need to dump planter boxes andswitch hybrids over the course of afield or farm but will be restricted toplanters with individual row hoppers.However, each refuge strip must be aminimum of six rows wide. This willbe impossible for producers withfour-row planters. Producers withsix-row planters could dedicate threerows to Bt and three rows to non-Bt.If you are in an area where pestpressure is traditionally high and yourgoal is to plant as much Bt corn aspossible, you are now restricted to the50 per cent level. The obviouscandidates for these alternating strips

are those producers with eight-rowor 12-row corn planters. Dedicatingthree end row units to non-Bt refugehybrids will effectively give you 38per cent (eight-row planter) and 25per cent (12-row planter) of yourcorn acreage as refuge. For reasonsmentioned earlier this more intimatepairing of hybrids require additionalcare in selecting refuge hybrids thatwill be compatible with your Bthybrid in terms of maturity, resistanceto lodging, etc.

Do not plant less than six rows ormix Bt and non-Bt seed because itmay allow the larva to travel and feedon both Bt and non-Bt hybrid, thusingesting an insufficient amount ofBt-toxin. The result is an increase inrisk of resistance development.

HEADLANDS/PERIMETER

Planting headland areas with non-Bthybrids is another option. Somequick calculations indicate thatdepending on the dimensions of thefield, headlands of 24 to 30 rows inwidth can generally meet the 20 percent requirement on fields up toapproximately 60 acres (again,depending on shape).

Bt CornBt Corn

SoybeansSoybeans

Bt Corn

NonBt

Corn

Bt CornNonBt

Corn

NonBt

CornNon Bt Corn

Bt Corn

Bt

Co

rn

No

n B

t C

orn

Bt

Co

rn

No

n B

t C

orn

Bt

Co

rn

No

n B

t C

orn

For example: a field 1,500 feetby 1,000 feet has a total of

34 acres and 24 rows (30-inchrow width) of headland wouldrepresent 6.5 acres or slightly

over 19 percent refuge.

20

What are the Impacts on Natural Enemies and other Non-Target Organisms?

Ladybird Beetle Adult

Many studies have shown that Bt Cry proteins are highly selective in managing larvae of the target pest species. Bt corndoes not affect beneficial insects including honey bees, ladybird beetles, green lacewing larvae, spiders, pirate bugs, damselbugs, syrphid flies or parasitic wasps. In addition, Bt corn for rootworm control does not affect beneficial soil arthropodsincluding centipedes, millipedes, carrion beetles, tiger beetles, crickets, ants, collembola, or earthworms.

However, indirect effects on natural enemies could occur. Predators, parasites and pathogens of the corn borer or cornrootworm larvae might decline as these pest populations decline. Refuge areas may moderate these indirect effects. Potentialdeclines in beneficial species are predicted to be much less than one would expect if a foliar insecticide were to be used.

On-going research is being conducted to ensure that key beneficial and other non-targets insects are not being affected byBt corn technology.

Green Lacewing Larva Syrphid Fly Adult Damsel Bug

The monarch butterfly is one of the mostrecognized and beautiful butterflies found inNorth America. It has four distinct life stages:egg, larva, pupa and adult butterfly with thelarvae entirely dependent on the commonmilkweed for food. Initial U.S. laboratorystudies conducted in 1999 found that themortality rate of monarch larvae increased when fed milkweed leaves that weredusted with Bt pollen. A collaborative research effort across the U.S. Corn Belt andOntario (University of Guelph) was undertaken to address the potential questionsthis study posed. These studies expanded on the extensive risk assessment already

completed for Bt corn on non-target insects, but also specifically addressed theimpact of Bt pollen on the monarch butterfly and other caterpillar species.The main conclusions from the subsequent studies were that Bt corn hybridsgrown in Ontario and throughout the Corn Belt of North America pose anegligible threat to monarch butterfly larvae.

Final Report on the Ecological Impact of Bt Corn Pollen on the MonarchButterfly in Ontario can be found at:http://www.inspection.gc.ca/english/plaveg/bio/bt/btmone.shtml

Full details on the research conducted can be found at:http://www.ars.usda.gov/is/br/btcorn

What About the Monarch Butterfly?

Amino Acids:Building blocks of proteins.

Bacillus thuringiensis (Bt):A group of naturally-occurring soilbacteria that occur worldwide andproduce protein toxins specific tocertain insects ( e.g. moths, beetles,blackflies or mosquitoes).

Biotechnology:Biotechnology is the application ofscience and engineering in the director indirect use of living organisms, orparts, or products of living organismsin their natural or modified forms.

Cry Proteins:Any of several proteins that comprisethe crystals found in spores of Bacillusthuringiensis.Activated by enzymes in an insect's midgut, these proteins attackthe cells lining the gut, cause gut paral-ysis and subsequently insect death.

Deoxyribonucleic Acid (DNA): Double-stranded molecule, consistingof paired nucleotide units groupedinto genes and associated regulatorysequences.These genes serve asblueprints for protein constructionfrom amino-acid building blocks.

Event:Successful transformation of anorganism by insertion of geneticmaterial (DNA). Events vary in thecomposition of the genetic packageinserted into the organism and theparticular location of insertion intothe host DNA.

Expression:Production of the desired trait (e.g.,Cry protein) in a transgenic plant.Expression varies with the gene, itspromoter and its insertion point inthe host DNA.

Gene:The basic unit of inheritance anddiversity; a section of DNA that codesfor a specific product (e.g., protein) ortrait.

Genetic Diversity:The huge variety in DNA sequencesfound in different organisms, that isresponsible for the wide variety ofplants and animals in the world.

Genetic Marker:Sequence of DNA that can easily beidentified and which therefore can beused as a reference point for mappingother genes.

Genetic Modification:Describes a series of techniques usedto transfer the genes from oneorganism to another, or to alter theexpression of an organism's genes.

Heredity:The transfer of genetic informationfrom parents to their offspring byreproduction (e.g., leaf shape).

High-Dose Strategy:An approach for minimizing the rapidselection for resistance to transgenicplants by using plants that produceCry proteins at a concentrationsufficient to kill all but the mostresistant insects.

Host Plant Resistance:Ability of a plant to avoid insectattack, kill attacking insects or toleratetheir damage.

Integrated Pest Management (IPM): A management approach thatintegrates multiple, complementarycontrol tactics (e.g., biologicalcontrol, crop rotation, host plantresistance, insecticides) to managepests in an effective, yetenvironmentally sound manner.

Marker Gene:A genetic flag or trait used to verifysuccessful transformation, and toindirectly measure expression ofinserted genes. For example, a geneused as a marker in BT 11 conferstolerance to the herbicide Liberty™.

Mode-of-Action:Mechanism by which a toxin kills aninsect. For example, the mode-of-action of Bt is ingestion anddisruption of cells lining the midgut.

Organism:A living plant, animal or microbe.

Promoter:A DNA sequence that regulateswhere, when, and to what degree anassociated gene is expressed.

Protein:A molecule composed of many aminoacids.There are many types of proteinswith a wide range of functions.

Refuge:An area of corn planted without theBt trait where susceptible pests cansurvive and produce a localpopulation capable of inter-matingwith any possible resistant survivorsfrom Bt corn.

Resistance:The capacity of an organism to surviveexposure to a control measure.

Resistance Management:A proactive process of limiting ordelaying resistance development in apest population with a focus onpreserving susceptible genes(individuals).

Selection:A natural or artificial process thatresults in survival and better repro-ductive success of some individuals over others. Selection results in geneticshifts if survivors are more likely tohave particular inherited traits.

Transgenic Plant:A plant which one or more genes,genetic constructs, or traits have beenintroduced using recombinant DNAtechniques, which could beconsidered to include the insertion ofgenetic material from the same ordifferent species.

Glossary of Basic Biotechnology Terms

21

22

Bt Field Layout

DETAILS / COMMENTS:

N

23

Notes

www.cornpest .ca