How Do Bugs Survive Exposure To Insecticides? Can We Use This Knowledge Against Them?

Insecticide resistance can result in product failures and pest infestations getting out of control. Does that mean all hope is lost? How can people stop insecticide resistance from happening? This week’s blog provides a little knowledge about the traits that allow insects to survive exposure to an insecticide and ways we can prevent this phenomenon from occurring. ​

Scientists challenge insects with different concentrations of pesticide as one way to investigate insecticide resistance.

Scientists group insecticides into classes based on different commonalities they share, such as the way they kill bugs (e.g., their mode of action). For example, the class of insecticides called organophosphates (OPs) all work by interfering with an enzyme involved in nerve function. By interfering with this enzyme, normal nerve signals fail, the insect’s behavior changes, and ultimately, the insect dies. The enzyme affected by the OP is called the target site. The target site is the exact place where the pesticide exerts its killing action.

How is all of this related to insecticide resistance, though? When people repeatedly use products with the same mode of action, resistance can develop. In groups of bugs, a variety of individuals exist with unique physical and behavioral characteristics—and some of them may have genetically based traits that make them less likely to die from pesticide exposure. Using a pesticide kills the majority of individuals in the population. With enough time, the repeated use of the same or similar pesticides kills the susceptible members of the population until only the individuals that can survive exposure remain.

WHAT KIND OF TRAITS ALLOW AN INSECT TO SURVIVE EXPSOURE TO AN INSECTICIDE?

Scientists have identified relatively few ways that insects use to survive exposure to an insecticide.

1. Metabolic resistance. Some insects overproduce or have a more efficient version of an existing enzyme that prevents the insecticide from reaching the target site. Metabolic resistance is the most common mechanism of insecticide resistance.
2. Target-site resistance. Target site resistance occurs when a change at the insect’s target site prevents the insecticide from fully interfering with that process.
3. Penetration resistance. Penetration resistance occurs when the absorption of the insecticide is slowed. A great example of this is the thickening of some bed bugs’ skin, which slows the entry of the insecticide into the body.
4. Behavioral resistance. Insects can avoid an insecticide by changing their normal behaviors. For example, German cockroaches started avoiding sugar baits because the baits often contained an insecticide.

​An insect may possess one or multiple traits simultaneously. For example, German cockroaches and bed bugs are notorious for possessing more than one of these mechanisms of resistance at a time.

HOW CAN WE DELAY RESISTANCE?

Scientists have devised several strategies to delay insecticide resistance. One method involves rotating between different products with different modes of action. By using products that kill bugs in different ways at different times, there is less pressure to select for specific mechanisms of resistance. The Insecticide Resistance Action Committee (IRAC) and the EPA have made it easier to understand what class of insecticide a product has by putting the information directly on some product labels. ​

Jennifer Gordon making an insecticide solution for resistance experiments.

Another strategy uses a product that has two different modes of action (combination product), or a tank-mix. By using multiple modes of action at once, hopefully there will not be individuals in the population with the right mechanism(s) of resistance to overcome simultaneous killing methods. However, over long periods of time, this method may still select for insecticide resistance. For more information on tank mixing, visit the Pesticide Environmental Stewardship website.

Maintaining susceptible individuals with susceptible genes that can interbreed with resistant individuals may also delay resistance. In agriculture, pest managers may do this by not spraying dedicated areas within or near fields to create safe spaces or refuges for susceptible insects. However, in some environments like people’s homes, allowing any insects to persist may not be acceptable.

FINAL THOUGHTS

Evolution is a process that allows animals to survive, even in changing environments. Thus, we should not be surprised that insects can adapt to environments where insecticides are applied. As of now, over 500 species of insects demonstrate some form of insecticide resistance. Once a population has become resistant, professionals have a challenge lessening that resistance.

Reversal of resistance can occur by allowing extensive time between applications of insecticides. However, this is not always reasonable, and no one can know if a resistant population will revert back to the same level of susceptibility. The best way to stop resistance is preventing resistance. With a little bit of knowledge, everyone from consumers to professionals can help delay the selection of resistance.

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