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Abstract
Bacillus thuringiensis subsp. israelensis (Bti) preparations are widely used for culicid larvae. There is no suitable commercially available analytical method for Cry4 toxin as active ingredient in Bti preparations. To overcome this limitation, an enzyme-linked immunosorbent assay (ELISA) was developed for quantitative determination of Cry4 toxin allowing a limit of detection (LOD) of ∼2 ng ml−1 in water. Preconcentration of aqueous samples by lyophilisation resulted in low but reproducible recoveries (25.7±6.8%), and the practical LODs for Bti preparations VECTOBAC WDG granulate and VECTOBAC 12 AS suspension were found to be ∼170 ng ml−1 and ∼900 ng ml−1, respectively. ELISA determinations indicated a rapid decay in detectable concentrations of VECTOBAC WDG applied at 400 ng ml−1 concentration in surface water: detected concentrations decreased by 18% and 44% in 4 days in water collected from two locations, and dropped below LOD afterwards. Larval mortality of Aedes aegypti indicated a continuous decrease even thereafter. Thus, quantitative Cry4 toxin detection facilitates proper timing and frequency of treatments to achieve optimal efficacy.
Acknowledgements
This work was funded by projects GOP-1.3.1-07/1-2008-0049 by the National Development Agency and MONTABIO (OM 00029/2008) by the National Office for Research and Technology of Hungary. The Authors wish to express their appreciation to Prof. Guenther Stotzky for providing the facilities for Cry4 protein purification and Cry4 specific antiserum production at the Laboratory of Microbial Ecology, Department of Biology, New York University, New York, USA.