Control of sewage filter flies using Bacillus thuringiensis var. israelensis—I. Acute toxicity tests and pilot scale trial

The possible use of the entomopathogenic bacterium, Bacillus thuringiensis var. israelensis ( Bti) to control fly nuisance associated with sewage filter beds was investigated. Acute toxicity tests using Teknar ®, a commercial formulation of Bti, showed it to be toxic to the nuisance species Limnophyes minimus, Metriocnemus hygropetricus, Psychoda severini and Sylvicola fenestralis. Twenty-four h LC 90 values for these species ranged from 1.1 × 10 5 to 5.5 × 10 7 spores cm −2. The application of Bti (Teknar ®) to pilot scale filter beds to give a theoretical concentration of 1.4 × 10 9 spores cm −2 of medium in the top 15 cm of each treated bed successfully killed almost all M. hygropetricus and P. severini larvae present without seriously reducing the efficiency of sewage treatment. The non-target organisms—Microturbellaria, Nematoda, Naididae, Lumbricidae, Collembola and Acari—were unaffected.