Factors affecting the efficacy of three commercial formulations of Bacillus thuringiensis var. israelensis against species of European black flies

The efficacy of three commercial formulations of Bacillus thuringiensis var. israelensis against two European black fly species was determined. The effect of seston concentration, temperature and larval size on the efficacy of the formulations was also determined. Teknar‐WDC was found to be almost four times as effective as Bactimos‐WP though only slightly more efficient than Vectobac‐AS against Simulium variegatum gp. larvae. Small larvae ( < 2.5 mm) were more susceptible to both Teknar‐WDC and Vectobac‐AS than large larvae ( > 5 mm) though no difference was seen with Bactimos‐WP. High seston concentrations both before and during bioassays significantly decreased the efficacy of all formulations. Increased temperatures increased the efficacy of all formulations.