97 - A statistically rigorous but organism and time efficient framework for determination of median lethal dose or concentration in insects

Abstract: The median lethal dose (LD₅₀) is the standard measure used in human and vertebrate pharmacology and toxicology and is also an important parameter derived from some insect bioassays. Median lethal dose is a critical parameter used to quantify the intrinsic efficacy of a pesticide, to quantify the intensity of insecticide resistance, and to allow comparisons of chemicals, populations, species, and temporal comparisons. Ethical issues and cost concerns have driven the development of formalized, parsimonious methods to accurately determine LD₅₀ in vertebrates and the resulting LD₅₀s are considered reliable and accepted by FDA and EPA.

Bioassays to determine arthropod LD₅₀ (and median lethal concentration - LC₅₀) have not adopted these efficiencies that have become standard in vertebrate toxicology. Current arthropod bioassays are time consuming and require testing of several hundred organisms over several days to generate rigorous results. In this presentation, we introduce modifications of the existing topical method to determine LD₅₀ and modifications of the larval bioassay method to determine LC₅₀ that allow determination of these parameters from as few as 120 insects in a single assay. We show that Low Input Topical (LIT) and Low Input Larval (LIL) assay methods produce results equivalent to the standard methods with similar coefficients of variation but require reduced effort. We also demonstrate several useful applications of these methods, including parsing out the toxicologic effect of genetic mutations without requiring isolation, determining LD₅₀ directly from species not easily colonized, and quantifying insecticide resistance to multiple active ingredients in Culex quinquefasciatus from locations in a Florida county using quantities of organisms comparable to that of the standard CDC bottle bioassay which does not quantify resistance.