What is the term for the reduction in effectiveness of one or more pesticide components when two or more pesticides are combined?

What is the term for the reduction in effectiveness of one or more pesticide components when two or more pesticides are combined?

• A. Antagonism
• B. Synergy
• C. Additivity
• D. Potentiation

Answer: (A)

Antagonism is when two pesticides interact in a way that makes the overall control weaker than what you’d expect from simply adding their individual effects. Think of it like this: if each pesticide on its own provides a certain level of pest kill, you’d predict the mixture to produce at least that much effect, and often a bit more if they work well together. When the actual combined effect falls short of that expectation, that shortfall is antagonism. A helpful way to picture it is to compare to an additive expectation. If pesticide A kills 40% of the pests and pesticide B also kills 40% under the same conditions, the predicted additive kill is 64% (you still have 36% of pests left after A, and 40% of the remaining are killed by B, so 1 - 0.6 × 0.6 = 0.64). If the mixture ends up killing less than 64%, the interaction is antagonistic. This differs from synergy, where the combined effect is greater than the additive expectation; additivity, where the effect matches the additive prediction; and potentiation, where a non-active substance increases the potency of a toxicant.

Antagonism is when two pesticides interact in a way that makes the overall control weaker than what you’d expect from simply adding their individual effects. Think of it like this: if each pesticide on its own provides a certain level of pest kill, you’d predict the mixture to produce at least that much effect, and often a bit more if they work well together. When the actual combined effect falls short of that expectation, that shortfall is antagonism.

A helpful way to picture it is to compare to an additive expectation. If pesticide A kills 40% of the pests and pesticide B also kills 40% under the same conditions, the predicted additive kill is 64% (you still have 36% of pests left after A, and 40% of the remaining are killed by B, so 1 - 0.6 × 0.6 = 0.64). If the mixture ends up killing less than 64%, the interaction is antagonistic.

This differs from synergy, where the combined effect is greater than the additive expectation; additivity, where the effect matches the additive prediction; and potentiation, where a non-active substance increases the potency of a toxicant.