Cross-resistance means resistance to...

• A. Similar pesticides
• B. Dissimilar pesticides
• C. All pesticides
• D. A single pesticide

Answer: (A)

Cross-resistance happens when a pest population that is resistant to one pesticide also shows resistance to other pesticides that are similar in how they work or in their chemical class, because the same resistance mechanism affects multiple products. That’s why the best answer is the idea of similar pesticides: the shared mode of action or chemistry means the pest’s defense works against several of them. If pesticides are different in how they act, the same resistance mechanism is less likely to confer protection, so cross-resistance to dissimilar pesticides isn’t as common. It isn’t about being resistant to all pesticides, nor just to a single one. An example is a pest with a target-site change that makes acetylcholinesterase less sensitive to multiple organophosphates, or a detoxifying enzyme that removes several compounds within the same chemical class.