A 24-h potato-based toxicity test for evaluating Bacillus thuringiensis var. israelensis (H-14) against darkwinged fungus gnat Bradysia impatiens Johannsen (Diptera : Sciaridae) larvae

A rapid and inexpensive acute toxicity test was developed and validated to evaluate formulations of the entomopathogenic bacterium, Bacillus thuringiensis Berliner var. israelensis (Serotype H-14) de Barjac (Bti) against laboratory-reared second instar larvae of Bradysia impatiens Johannsen (Diptera: Sciaridae), a pest of greenhouse and nursery crops. The test, based upon larval darkwinged fungus gnat attraction to potato starch as a food source, yielded results in 24 h and was inexpensive to conduct. Using written standard operating procedures, validation data were collected using a Bti formulation from a single lot to validate the method through QA/QC methods and develop a database for employing the toxicity test as a bioassay. The bioassay might be suitable for use with other biological and chemical pesticides, to assist insecticide product development efforts, for quality control testing, for formulation evaluation, and for efficacy comparison between pesticides.