Bioassay

Definition

A quantitative or semi-quantitative analytical method that measures the potency, toxicity, or biological activity of a substance by its effect on living organisms, tissues, or cells. Bioassays may be quantal (yielding binary, all-or-nothing responses such as mortality or emergence) or quantitative (yielding graded responses such as growth rate, enzyme activity, or behavioral change). In entomology, bioassays are essential for determining lethal concentrations (LC₅₀), resistance levels, pheromone activity, and mode-of-action studies.

Etymology

From Greek bios (life) + Old French assai (trial), via English assay.

Example

A standard contact bioassay for pyrethroid resistance in Anopheles mosquitoes exposes adult females to treated filter paper for a fixed duration, then records mortality at 24 hours to calculate the resistance ratio compared to a susceptible strain.

Synonyms

• biological assay
• living-system assay

Related Terms

• LD50
• LC50
• dose-response curve
• toxicity testing
• insecticide resistance
• no-choice test
• probit analysis
• synergist bioassay

Usage Notes

Distinguish from purely chemical or physical assays that do not require biological response. In entomological toxicology, bioassays are typically standardized (e.g., WHO tube tests, leaf-dip assays) to ensure reproducibility across laboratories. The term is broader than 'toxicity test'—bioassays can measure stimulatory, attractant, or developmental effects, not just lethality.