Insect Traits Evolving for Ongoing Bug Battles

From Cotton Grower Magazine – August/September 2016

bollworm1-ncsu-web Photo: North Carolina State University



American cotton producers of a certain age can attest to how much of a blessing Bt traits have been on the farm. Bollgard first appeared in 1996, and farmers were suddenly able to control earworm and tobacco budworms without the excessive spraying they had become accustomed to.

Years later, a second generation of Bt traits arrived, providing dual gene activity. Bollgard II from Monsanto, WideStrike from Dow AgroSciences and TwinLink from Bayer CropScience all provided improved control of lepidopterist pests.

“Our Bollgard II and TwinLink both have Cry-1 AC and Cry-2 AB, which are very good against corn earworm and tobacco budworm,” said Scott Graham, a graduate research assistant with University of Tennessee Extension. “The WideStrike has Cry-1 F which is better against fall armyworm.”

But as with all crop protection technologies, Mother Nature provides a constantly moving target.

“Now we’re starting to see a little decline with those, and so we’re moving into our third generation Bt products, which have three genes for control against lepidopteran pests,” Graham said.

Graham addressed a crowd of cotton producers at the Milan No-Till Crop Production Field Day, hosted by the University of Tennessee Ag Research and Education Center. He reminded the crowd there that Dow’s third generation insect trait, WideStrike 3, has been commercially available since 2014, while Bayer’s TwinLink Plus and Monsanto’s Bollgard III should be commercially available “in the pretty near future.”

Those two technologies will arrive just in time, according to Graham, because they provide noteworthy improvements in pest control over the second generation Bt traits. In 2015 field trials based in Jackson, TN, Dr. Scott Stewart with University of Tennessee Extension “could not find a single damaged boll” in his Bollgard III plots that were sprayed. The same could be said for the varieties that feature the TwinLink Plus trait. These findings were especially encouraging, given some of the reports that have come in from across the Cotton Belt regarding a lack of efficacy among the second generation insect traits.

“I know in some areas of the country they are having to spray a lot more, starting to get some resistance and stuff going,” Graham said. “It is important still to be on the lookout for pests and make sure you know what’s going on in your field.”

This is not to say that the second generation insect traits are not still highly effective. According to Graham, Bollgard II varieties still demonstrated 95% reduction in boll damage compared to non-Bt varieties in their plots.

And third generation insect traits will certainly reduce insect control applications, but as Graham said, they will not provide a silver bullet.

“There are still going to be instances where you need to spray, even on WideStrike 3 cotton where we’re seeing no boll damage,” Graham said. “You’re still going to have to spray every once in a while. It’s just unavoidable.”

Of course, any reduction in sprays is a good thing, especially in a year when prices are lagging and margins are thin.

“Saving sprays means saving money, saving trips across the field, and saving us from encouraging insect resistance management,” Graham says.