Trait Table Update

Insect Resistance Issues Showcased in 2017 Handy Bt Trait Table

Emily Unglesbee
By  Emily Unglesbee , DTN Staff Reporter
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The failure of the Herculex trait, Cry1F, to protect many cornfields from western bean cutworm in 2016 prompted a new column on compromised Bt traits in Michigan State's Handy Bt Trait Table. (Photo courtesy of Andy Michel, Ohio State University)

ROCKVILLE, Md. (DTN) -- If you are planting Bt corn this year, there's a new tool to help you determine if your hybrids' traits are still effective against the pests they claim to control.

Each year, Michigan State University entomologist Chris DiFonzo produces the Handy Bt Trait Table, which lists which Bt corn hybrids contain which Bt proteins, as well as the insects they target. This year, a new column will also alert growers to traits that may be "locally or regionally ineffective" because of suspected or documented insect resistance.

DiFonzo's trait table has become an invaluable tool for growers, scientists and other members of the ag community as cross-licensing between companies has turned Bt corn products into a confusing tangle of traits and brand names. The table cuts through this marketing maze by showing how just nine Bt proteins are grouped and repackaged among corn hybrids from Dow AgroSciences, DuPont Pioneer, Monsanto, Syngenta and their licensees.

The new column of regionally ineffective traits was inspired by the collapse of Cry1F (the Herculex trait) against populations of the western bean cutworm in parts of the U.S. last year, including the Great Lake states and the eastern Cornbelt, DiFonzo said.

A group of entomologists from those states sent a letter in October to the Cry1F registrants asking them to remove the western bean cutworm from the Cry1F label, where it is listed as an insect the trait controls. (See the DTN story here:…)

DiFonzo at first considered simply removing western bean cutworm from the Handy Bt Trait Table's list of insects controlled by Cry1F, but ultimately decided to create a new column for all compromised Bt traits.

"I decided it still is useful for farmers to know what insects the trait is supposed to work against and what it is labeled for, since maybe there are still some [places] where they will see some efficacy or some suppression," she told DTN.

"This column is intended to alert growers and consultants to potential management problems, influence seed selection, and encourage field scouting," the introduction to the table adds.

The new column is based on scientific literature and communications reporting either documented resistance or suspected resistance based on field failures of the trait.

Here are the Bt traits that are currently compromised by documented or suspected resistance in Lepidoptera (moths and caterpillar) populations:

-- Cry1F (Herculex 1) -- fall armyworm, western bean cutworm and southwestern corn borer

-- Cry1Ab (YieldGard Corn Borer) -- corn earworm and sugarcane borer

-- Cry1A.105 x Cry2Ab2 (YieldGard VT Pro) -- corn earworm

-- Cry3Bb1 (YieldGard Rootworm) -- western corn rootworm

-- mCry3A (Agrisure RW) -- western corn rootworm

-- eCry3.1Ab (Agrisure Duracade) -- western corn rootworm

-- Cry34/35Ab1 (Herculex RW) -- western corn rootworm

Note that the western corn rootworm now has documented resistance to all four Bt proteins marketed for its control.

You can find the new 2017 Handy Bt Trait Table here: The table now covers all U.S. corn production, thanks to assistance from DiFonzo's co-authors, Texas A&M entomologist Pat Porter and Ohio State entomologist Kelley Tilmon. (Past versions used two tables, one for Southern growers and one for Midwestern growers.)

You can also see the studies DiFonzo used to identify which traits were compromised here:…. However, this is not a comprehensive list of all Bt trait failures, and growers should contact their local Extension office to see if insect populations in their region have shown resistance to the Bt traits listed as regionally ineffective in the new trait table.

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Emily Unglesbee