Insecticide applications and resistance

Main

Insecticides are substances used to control insect pests that damage crops, spread diseases, or are a nuisance. They are widely used in agriculture to protect crops and increase yields. Insecticides work through various modes of action, such as disrupting the nervous system, inhibiting energy production, or regulating growth. Common types include organophosphates, carbamates, pyrethroids, and neonicotinoids.

However, the repeated use of insecticides with the same mode of action can lead to insecticide resistance - a heritable change in the sensitivity of a pest population that results in the repeated failure of an insecticide to achieve the expected level of control when used as recommended. Resistance develops through natural selection of rare, pre-adapted resistant individuals that survive insecticide exposure and pass on the resistance trait to their offspring.

For example, the Colorado potato beetle has developed resistance to over 50 different insecticides.

Terms

• Cross-resistance: Resistance to one insecticide that confers resistance to another, even when the insect has not been exposed to the latter product.

• Insecticides: Substances used to control insect pests that damage crops, spread diseases, or are a nuisance.

• Metabolic resistance: Overexpression of enzymes that detoxify insecticides, rendering them ineffective.

• Mode of action (MOA): The specific process by which an insecticide kills an insect or inhibits its growth.

• Multiple resistance: When an insect population resists two or more insecticide classes with different modes of action by expressing multiple resistance mechanisms.

• Target-site resistance: Changes in the target site that reduce the binding of the insecticide, leading to insensitivity.

Analogy

Insecticide resistance is like antibiotic resistance in bacteria. Overusing the same antibiotic selects for resistant bacteria that survive and multiply. Soon the antibiotic becomes ineffective against infections. Similarly, overusing insecticides with the same mode of action selects for resistant insects that eventually become dominant, making the insecticide ineffective.

Misconception

Many believe insects develop resistance only after repeated exposure over many generations. In reality, resistance arises from rare individuals with pre-existing resistance traits that are selected for and enriched by insecticide applications. The speed of resistance development depends on factors like insect reproduction rate, migration, and insecticide application practices.

History

• 1940s: Introduction of synthetic organic insecticides like DDT

• 1947: Resistance to DDT confirmed in houseflies

• 1950s-1990s: With each new insecticide class introduced, resistance appeared within 2-20 years in key pests

• 2000s-present: Over 500 pest species have developed insecticide resistance, increasing at alarming rates

How to Manage Resistance

• Monitor pest populations and apply insecticides only when needed based on economic thresholds to avoid unnecessary use.

• Rotate insecticides with different modes of action to avoid repeatedly exposing pests to the same type.

• Use insecticide mixtures that combine two or more modes of action.

• Employ non-chemical control methods like crop rotation, resistant plant varieties, and biological control when possible to reduce selection pressure.

Facts

• Over 500 species of insects and mites have developed resistance to insecticides worldwide.

• Insects can develop resistance in as little as 2-20 years after a new insecticide class is introduced.

• The house fly was one of the first insects to develop resistance, showing resistance to DDT by 1947.

• Resistance develops fastest in enclosed settings like greenhouses, where insects reproduce quickly and there is little immigration of susceptible individuals.

• An estimated 10-30% of crops are lost each year to insect pests despite widespread insecticide use.