If a pest shows resistance to a pesticide and a second pesticide with a similar mode of action is also ineffective, this is an example of what concept?

• A. Cross-resistance
• B. Curative
• C. Cultural Control
• D. Directed application

Answer: (A)

Cross-resistance happens when a pest that has become resistant to one pesticide also shows resistance to another pesticide that works in the same way. The pest has a resistance mechanism—like a change in the pesticide’s target site or an enhanced ability to detoxify the chemical—that affects multiple products sharing that mode of action. So even though the second pesticide is not the exact chemical, it still targets the same site or uses the same biochemical pathway, and the pest isn’t killed as effectively.

This isn’t about curing existing pests (curative) or about using non-chemical methods (cultural control) or applying chemicals in a targeted way (directed application). Those concepts describe different approaches or outcomes, not the resistance pattern where one resistance extends across a class of similar-action products.