Effects of freezing and field-collected substrates on the efficacy of Bacillus thuringiensis serovar. israelensis as determined through bioassays in the laboratory
1992
Tousignant, M.E. | Boisvert, J.L. | Chalifour, A.
Numerous field trials have been undertaken in order to obtain a deeper understanding of the behavior (persistence, dispersion, etc.) of Bacillus thuringiensis serovar. israelensis (B.t.i.) formulations when treating rivers or streams for blackfly control. After an extensive sampling of water and natural substrates (periphyton, sediments, moss), freezing is a useful procedure to prevent enzymatic deterioration or bacterial growth in samples before bioassays are to be performed. Using Aedes triseriatus neonate larvae, we quantified the effect on potency of freezing and thawing of B.t.i. suspensions at operational field concentrations. In addition, as samples varied in their content of natural substrates we tested the hypothesis that the presence of such suspended solids affected the mortality response of larvae. Our results showed that these parameters are of significant importance and should be accounted for when comparing bioassays performed on previously frozen or turbid samples.
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