The effects of algae on the efficacy of Bacillus thuringiensis var. Israelensis against larval black flies (diptera: simuliidae) in laboratory bioassays
Stephens, Marianne Shockley
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The effects of algae on the efficacy of Bacillus thuringiensis var. israelensis against larval black flies (Simulium vittatum IS-7) were investigated in laboratory bioassays. Microcystis, a blue-green algae, demonstrated no statistically significant effects on the efficacy of B.t.i. Navicula, a diatom, demonstrated significant effects at cell concentrations greater than 34,000 cells/ml. Scenedesmus, a green algae, also demonstrated significant effects at cell concentrations greater than 7,000 cells/ml. Negative effects of algae were reversed both by increasing the concentration of B.t.i. and to a lesser degree by increasing exposure period. Differences attributable to introduction time of algae and B.t.i. into the bioassay could not be determined from our experiments. Residual toxicity determinations using the Aedes aegypti bioassay revealed that, if given the opportunity, black flies ingest significantly more algae and B.t.i. particles in an increased exposure period.