Managing insecticide resistance

Like weeds, insects can develop resistance to the pesticides used to control them. While trait technology, like Bt (Bacillus thuringiensis), have revolutionized insect management, farmers still need to be vigilant and actively manage for insect resistance. And that’s where Bayer Traits can help.

How does insecticide resistance develop?

There are four ways that insects can develop resistance to insecticide products:²

1. Metabolic resistance is when insects are able to metabolize the toxin in the insecticide and get it out of their bodies quickly. This is the most common cause of insecticide resistance.

2. Penetration resistance is almost the opposite of metabolic resistance in that resistant insects develop the ability to absorb toxins much slower than susceptible insects, thereby neutralizing the intended effects.

3. Altered target-site resistance occurs when the biological site where the toxin is supposed to bind within the insect has been altered genetically over time. This is very similar to how some weeds develop herbicide resistance.

4. Behavioral resistance is when insects simply learn to recognize the danger and avoid contacting or ingesting insecticidal toxins. They may stop feeding, or leave the treated area by moving to a different part of the plant or flying away altogether.

As with herbicide resistance, intensive use of insecticides from the same chemical class can be a major contributor to insect selection and resistance. But insects can be a harder target than weeds in that some species produce more than one generation per season (allowing for faster adaptation to insecticides), and some have large migration areas, meaning you cannot control what farmers do in other far away regions that may impact insecticide resistance.

What about insect trait technologies, like Bt?

Since 1996, trait technology has transformed how Canadian farmers manage insects in some crops, particularly corn. Bt crops produce certain proteins that have insecticidal activity against targeted insects – they basically protect the plant from within and, in doing so, reduce the need to spray more traditional insecticides.

In recent years, however, populations of European corn borer and Western bean cutworm have developed resistance to one strain of Bt protein (Cry1F),³ showing that insects can overcome even this powerful tool.

It should be emphasized that insect resistance to Bt has been documented only in crops with one Bt protein present, and that those with multiple, or stacked, Bt proteins are still effective.

What to do about insecticide resistance today

Insecticide resistance, like herbicide resistance, can be effectively managed by using an integrated pest management (IPM) strategy that combines cultural and chemical practices to delay or prevent the onset of resistance. These include:

• Scout and monitor. As with any crop pest, timely crop scouting is step one when it comes to assessing what insects might be present and in what quantity. If you find a pest with the potential to cause economic damage, monitor it carefully to determine if and when an insecticide application is needed.
• Know the economic thresholds. Spray insecticides only when insect populations are large enough to cause economic crop loss. Spraying when insect numbers are too low can cause selection pressure on the population and lead to insecticide resistance.
• Apply insecticides correctly. Time applications when insects are most vulnerable, which is usually when they’re small and just emerging. Apply at recommended rates and timings to get the best results.
• Keep switching it up. Keep insects off balance with crop rotations, changing up your trait packages, adjusting planting dates, using a layered insecticide approach (seed treatments, in-furrow applications and spraying), managing overwintering areas and, if possible, rotating insecticide classes
• Choose crops with stacked traits. Stacked traits mean more than one mode-of-action to go after yield and quality-robbing insect pests, which can delay the onset of resistance.

Bayer Traits can help fight insecticide resistance

Already, Bayer offers farmers leading traits that help control above and below ground insects. Traits such as:

• SmartStax® RIB Complete® corn hybrids have multiple modes of action against black cutworm, corn earworm, corn rootworm, European corn borer and fall armyworm.
• Trecepta® RIB Complete® corn hybrids also carry multiple modes-of-action against above-ground corn insect pests, including Western bean cutworm.
• The VT Double PRO® RIB Complete® line of corn hybrids provide two modes-of-action to protect against key stalk- and ear-feeding insects.

Canadian farmers can also look forward to a new generation of powerful, transformative trait technologies designed to take protection against insects to a new level, including:

• SmartStax® PRO with RNAi technology. This is the agriculture industry’s first RNAi-based trait against corn rootworm that offers greater root node protection in corn.
• VT4PRO with RNAi technology

If you have questions about insecticide resistance on your farm, talk to your crop advisor.

Sources:

¹ Entomology Today (PDF of original Melander article): https://entomologytoday.org/wp-content/uploads/2014/04/melander-jee-1914.pdf

² Insecticide Resistance Action Committee (IRAC), Resistance: The Facts – History and overview of resistance. https://irac-online.org/content/uploads/Resistance-The-Facts.pdf

³ Carolyn King, Insect resistance to BT corn, Top Crop Manager, February 2020. https://www.topcropmanager.com/insect-resistance-to-bt-corn/