Spectroscopically Derived Spread Factors for Different Bacillus ThuringiensisInsecticidal Formulations on Paper Impaction Cards

摘要

The U.S. Department of Agriculture Forest Service (USDAFS) uses Bacillusthuringiensis (BT) formulations in their insecticidal spraying programs. The USDAFS monitors the coverage and droplet size distribution achieved using witness cards. The collected aerosol stains (enhanced with a dye tracer in the fluid) are converted to original droplet sizes using a predetermined spread factor regression. Recently, a novel spread factor determination method was developed and tested with neat and polymer thickened organic liquids. This method used actual trial stains and spectra properties of the tracer dyes in the test fluid. The dyes were removed by solvent extraction from individual stains on the witness cards and quantitatively spectro analyzed to determine original droplet size. This report evaluates this method's compatibility with USDAFS materials (witness cards, tracer dyes, and BT formulations). Several variables influencing the spread factor regression were investigated (e.g., solvent extraction efficiency, dye aging/degradation droplet impact velocity, witness card, material, solution composition, etc.). This method produced accurate and reliable spread factor relations when used with USDAFS materials. Errors (e.g, incomplete extraction, dye aging) were minimal if the stains were promptly (within 2 weeks) analyzed.