Fighting Resistance

Fighting Resistance

To outwit pests, growers need to evolve — fast.

Insect Resistance Management

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In the age-old battle between growers and insects, it’s not always clear who’s outsmarting whom. Even the best crop protection products can lose efficacy when insects adapt to resist them. In order to tackle this perennial problem, growers need to adopt a multi-faceted and ever-evolving plan of attackwhich is often easier said than done.

Insects are remarkably adept at “learning” to resist pest management tools. These aren’t limited to crop protection technology; even centuries-old techniques can lose effectiveness over time. The northern corn rootworm provides a great example. As Stephanie Kadlicko-Stare of DuPont Pioneer notes, these damaging insects “hatch and grow” alongside corn plants. The larvae feed on the roots, which can kill a plant if it is starved of needed nutrients and water. Without a strong root system, the corn plant can wither and may tip over and die. Rootworm populations are surprisingly hardy. “Eggs can lay dormant in the field for two or more years,” Kadilcko-Stare says, using an adaptation called extended diapause. When growers rotate cropsplanting soy instead of corn, for examplerootworm eggs can wait out the year and hatch just in time for the next planting of corn, their preferred crop. Over time, only the rootworms that have developed this extended diapause adaptation survive crop rotation, rendering that time-proven technique ineffective.

The rootworm isn’t the only savvy insect species able to thrive despite growers’ best efforts. Dr. Clint Pilcher, also of DuPont Pioneer, has studied the phenomenon extensively. “Resistance is not something that’s new,” he notes. “It’s been happening for decades. An insect will overcome or adapt to any technology that’s used against them over time.” In other words, every strategy has a shelf life and the best that pest-control experts can do, Pilcher says, is to try and manage how much time each control option will be effective.

Like agriculture itself, resistance varies tremendously depending on local climate. One notable struggle is taking place now in Brazil, where Spodoptera frugiperda, also known as the fall armyworm (FAW), is wreaking havoc for corn growers. In North America’s temperate climate, says Pilcher, “That insect only goes through two or three generations a year. But in Brazil, it’ll go through eight to ten cycles. And every cycle you go through, you’re selecting for the individuals who are able to survive.” In other words, the FAW can evolve resistance four to five times quicker in a tropical area like Brazil, which has a huge impact on growers’ ability to manage successfully. Pilcher estimates that a control technology which could be used in the United States 12-15 years may only last three or four years in Brazil.

Pilcher and others at DuPont are working on protocols and strategies to protect Brazil’s corn output, which Bloomberg recently reported has doubled over the past decade, and will likely reach 53 million tons this year. Brazil is still relatively new to corn production, and there’s a steep learning curve for growers when it comes to pest management. Pilcher recommends an integrated pest management system that applies an ever-changing cast of methodologies to “outsmart” insects. This involves alternating sprays, crop rotation, and the use of engineered seeds to delay the onset of resistance to any one tool.

Refuges are portions of planted fields that do not contain a biotech trait, and are designated areas for insects to survive and reproduce. This, in turn, ensures that resistant pests aren’t dominating the gene pool. It’s a simple strategy, but it requires committing a portion of their arable land to seed that is not protected as well as the biotech-containing seed, so the strategy is often dismissed by growers in Brazil. Currently, Brazil does not enforce refuge requirements.

It’s a question that will need to be answered soon. Both Pilcher and Kadlicko-Stare emphasize the need to alternate and combine multiple modes of pest control, like genetic traits, chemicals, and seed treatments, with the goal of prolonging the viability of each tool. Pilcher is quick to emphasize that this issue will need to be addressed by multiple stakeholders; the old model of simply buying a product and using it the same way, year after year, no longer works. “Growers have to take a role in this, and not rely 100% on companies to develop new technologies,” he notes. “We have to change the way we manage this or we’re going to run out of tools, and growers will have to either plant a whole different crop or live with much lower yields than they experience today with these products.”

With so much at stake, it’s clear that this issue will be receiving attention for years to come. Pilcher and his team have recently traveled to Brazil for large-scale meetings to tackle the problem and implement large-scale guidance. It’s certainly worth the effort; as Pilcher notes, “Resistance has the capacity to cost growers and industry hundreds of millions of dollars.”