Nearly 20 Years of Bt Hybrids: What Have We Learned and Where Do We Go from Here?

16th SWCS-SSSA SymposiumGreensboro, NC

July 27, 2015

Michael E. GrayDepartment of Crop Sciences

University of Illinois, Urbana-Champaign

We have a transgenic landscape in the corn and soybean production system of the

midwestern United States.

“It is an exciting time in agriculture to witness the appearance of Bt corn technology. Farmers will experience the virtual elimination of their most serious insect pest coupled with corn yields that jump 10 to 20 bushels per acre. The advent of Bt corn will alter the course of insect pest management for decades. The burdensome complexity of crop scouting, calculating economic thresholds, and timing insecticide applications for the farmer will be replaced by the novel simplicity of planting a seed.” Pages 117-118

Marlin E. Rice, European Corn Borer Management and Transgenic Hybrids: Perspectives of an Extension Entomologist

Illinois Agricultural Pesticides Conference, Urbana, Illinois, January 3-4, 1996

According to a paper published in Science (Hutchison et al.,October 8, 2010), cumulative benefits for corn growers, due to widespread use of Bt hybrids during a 14-year period in Illinois, Minnesota, and Wisconsin were $3.2 billion. Of special interest is the estimate that more than $2.4 billion of this total went to producers who elected not to plant Bt corn.

Courtesy of M.E. Rice

Hutchison, W.D. et al. 2010. Science, Volume 330, pp. 222-225.

Summary of European Corn Borer Fall Surveys,University of Illinois Extension

1943-2009

Gray et al. 2009. Ann. Rev. Entomol. 54: 303-21.

Most expensive pest to control--western corn rootworm (Diabrotica virgifera virgifera): BBC News Science and Environment website: "Plant Pests: The Biggest Threats to Food Security?" (www.bbc.co.uk./news/science-environment-15623490)

Economic Impact of Bt Corn Rootworm Hybrids

Available commercially since 2003 2011 – 19.1million ha (47.2 million acres)

planted in the US (56% of US corn crop) Primary economic impact – greater yields ~ 5%

relative to conventional hybrids Net economic impact - $24/ha to $121/ha;

$9.71/acre to $48.97/acre Cumulative economic benefit from Bt corn

rootworm hybrids, since 2003 - $7.1 billion

Source: Brookes and Barfoot. 2013. GM crops: global socio-economic and environmental impacts 1996-2011. PG Economics Ltd, Dorchester, UK, April 2013.

Tinsley, N.A., R.E. Estes, and M.E. Gray. 2013. Validation of a nested error component model to estimate damage caused by corn rootworm larvae. Journal of Applied Entomology 137(3): 161-169.

15% yield loss per node of roots pruned

Lombardy Region of NW Italy, July 2014, Courtesy of Dr. C.R. Edwards

Ball, H.J. & G.T. Weekman. 1963. Differential resistance of corn rootworms to insecticides in Nebraska and adjoining states. J. Econ. Entomol. 56: 553-555.

Excessive use of broadcast chlorinated hydrocarbon insecticides (aldrin, heptachlor) for corn rootworm control, from the late 1940s through the early 1960s, resulted in the development of impressive levels of resistance (Ball and Weekman 1963).

http://www.inchem.org/documents/ehc/ehc/e91_2.gif

To date, resistance has not developed to the commonly used soil insecticides (granular/liquid formulations: organophosphates, pyrethroids) because they are delivered in-furrow or in a narrow band during planting. In effect, creating a refuge between rows.

http://blog.machinefinder.com/wp-content/uploads/2013/02/drills_1700_06_11_1_130729_N_942x458.jpg

http://beready.caseih.com/wp-content/uploads/2012/06/Case-IH-Early-Riser-1240-Planter-June-28-544x361.jpg

Meinke, L.J., B.D. Siegfried, R.J. Wright & L.D. Chandler. 1998. Adult susceptibility of Nebraska western corn rootworm (Coleoptera: Chrysomelidae) populations to selected insecticides. J. Econ. Entomol. 91: 594-600.

Meinke et al. (1998) confirmed that western corn rootworms have developed resistance to methyl parathion (16.4 fold) and carbaryl (9.4 fold) in areas of Nebraska where applications of these products have been common for years.

http://www.gearthblog.com/images/centerpivotirrigation.jpg

Felsot, A.S., J.G. Wilson, D.E. Kuhlman & K.L. Steffey. 1982. Rapid dissipation of carbofuran as a limiting factor in corn rootworm (Coleoptera: Chrysomelidae) control in fields with histories of continuous carbofuran use. J. Econ. Entomol. 75: 1098-1103.

Lack of persistence for certain insecticides (especially some carbamates) led to control failures in producers’ fields. The lack of persistence was eventually attributed to a phenomenon known as enhanced microbial degradation. Felsot et al. (1982) believed the rapid dissipation of carbofuran was related to its repeated use.

http://wsm.wsu.edu/mag_images/big_brother/2002Winter_survival4.jpg

Felsot, A.S., and D.R. Shelton. 1993. Enhanced biodegradation of soil pesticides: interactions between physiochemical processes and microbial ecology. Soil Science Society of America and American Society of Agronomy. Special Publication No. 32.

Levine, E., J.L. Spencer, S.A. Isard, D.W. Onstad & M.E. Gray. 2002. Adaptation of the western corn rootworm to crop rotation: evolution of a new strain in response to a management practice. Am. Entomol. 48(2): 94-107.

Gray et al. 2009. Annual Review of Entomology. 54: 303-21.

LaSalle County, IL, 2002 (first-year corn)

Courtesy of Dale Baird

Courtesy of Dale Baird

Period I, 2013 Period II, 2013 Period I, 2014 Period II, 20142011

10.0–19.9 Greater than 20.05.0–9.92.5–4.9Less than 2.5

Mean number of western corn rootworm beetles per 100 sweeps in soybean

Corn Rootworm Bt Proteins and Changing Refuge Requirements

http://news.illinois.edu/WebsandThumbs/gray,mike/cornseed1_b.jpg

Cry3Bb1mCry3ACry34Ab1/Cry35Ab1eCry3.1Ab

Severe Root Injury to Bt Plants (VT Triple PRO), Rotated Corn, Kankakee County, Illinois, August 26,

2013.

Bioassays (2014) have confirmed western corn rootworm resistance to Cry3Bb1 and mCry3A, as well as cross resistance between these proteins.

Western corn rootworm resistance to the Cry3Bb1 protein has been confirmed in numerous counties across Illinois. Cross resistance with the mCry3A protein has been confirmed in Kankakee and Livingston Counties – along with rotation resistance.

Tabashnik, B.E., D. Mota-Sanchez, M.E. Whalon, R.M. Hollingworth, and Y. Carriere. 2014. Defining terms for proactive management of resistance to Bt crops and pesticides. Journal of Economic Entomology 107(2): 496-507. “Resistance: genetically based decrease in susceptibility

to a pesticide” “Field-evolved resistance (= field-selected resistance):

genetically based decrease in susceptibility to a pesticide in a population caused by exposure to the pesticide in the field”

“Practical resistance (= field resistance): field-evolved resistance that reduces pesticide efficacy and has practical consequences for pest control”

“Finally, we note that there is an escalating use of insecticides directed at western and northern corn rootworm in areas of the Corn Belt where rootworm densities are low and the likelihood of economic injury is minimal. When insecticides overlay transgenic technology, the economic and environmental advantages of rootworm-protected corn quickly disappear. We are concerned that high commodity prices and other factors may have fueled an insurance-based approach to corn rootworm management, one that violates many tenets of IPM and that will only increase insect resistance development in the long term.”

How is EPA proposing to address corn rootworm resistance in Bt corn?

“EPA has proposed a framework intended to delay the problem of the corn rootworm pest becoming resistant to Bt proteins. The Agency is proposing requirements on the manufacturers of Bt corn including:”

• In areas at risk for corn rootworm resistance, to require crop rotation, use of corn varieties containing more than one Bt protein, or other Integrated Pest Management (IPM)  strategies and stewardship for corn rootworm.

• To develop and implement a strategy to better detect and address areas of resistance as they emerge.

• To use different and improved scientific tests and sampling to study the problem and more reliably ensure that resistance to the Bt corn proteins is identified.

“EPA’s proposed framework outlines that 70% of corn acres in the “red zone” should take part in IPM efforts and that 50% of corn acres in non-“red zone” areas should participate in IPM efforts. IPM efforts (e.g. crop rotation) are designed to prevent future problems rather than reacting to them once they occur. These measures and others are designed to significantly delay development of resistance in corn rootworms in areas planted with Bt corn.”

http://www.epa.gov/pesticides/biopesticides/pips/corn-rootworm.htm

Corn and soybean producers in the North Central Region of the United States are increasingly relying upon the use of two neonicotinoid insecticides applied as seed treatments: thiamethoxam (Cruiser ®) and clothianidin (Poncho®).

thiamethoxam

clothianidin

http://water.usgs.gov/nawqa/pnsp/usage/maps/show_map.php?year=2011&map=CLOTHIANIDIN&hilo=H&disp=Clothianidin

http://water.usgs.gov/nawqa/pnsp/usage/maps/show_map.php?year=2011&map=THIAMETHOXAM&hilo=H&disp=Thiamethoxam

DOI: 10.1021/es506141g

Nicotinoid Seed Treatments: Primary

Targets in Corn

Percentage of Plants Infested in Farmers’ Fields Over a 10-Year Period

Perc

enta

ge

Years Bigger and Petty (1965)

“This analysis provides evidence that U.S. soybean growers derive limited to no benefit from neonicotinoid seed treatments in most instances.”

18 land-grant entomologists – 13 states concur with respect to the North Central Region of USA.

“Have we learned anything? I’m afraid that we are continuing to make the same mistakes in insect management that we have made over the past 50 years. To be sure, the ingredients might have changed from DDT to genetically modified organisms, but the system appears much the same.” Turpin, F.T. 2000. Management of Insect Pests During the Past 50 Years:

Lessons Learned, Illinois Crop Protection Technology Conference, University of Illinois.

Is IPM relevant in the modern corn and soybean production

system? Fewer corn and soybean producers Increasing farm size Absentee landowners Pest management decisions

increasingly made by suppliers of inputs

Corn viewed as a biofuel, not just a food crop

http://www.livinghistoryfarm.org/farminginthe70s/media/machines_0801.jpg

Is IPM relevant in the modern corn and soybean production

system? Higher commodity prices in recent years – trending lower

Trait-driven market place Insecticidal/Fungicidal Seed

Treatments – The norm Paradigm shift from IPM to IRM Industry consolidations Integration of traits is the new

integrated management plan

Summary Comments Use of Bt hybrids remains very high across many Corn Belt

states. The use of neonicotinoids is extensive in the corn and soybean

agroecosystem and environmental concerns are beginning to emerge.

Western corn rootworms have developed resistance to Cry3Bb1 and mCry3A proteins in some areas of the Corn Belt and a resurgence of corn rootworm planting-time soil insecticides is occurring due to concerns regarding Bt resistance.

Producers are increasingly managing insect pests of corn and soybeans using an “insurance” based approach rather than relying on traditional (scouting and use of economic thresholds) or more integrated (IPM) approaches.

This new form of “IPM” (Insurance Pest Management) has become the norm in large-scale corn and soybean production in much of the Corn Belt.