Correction of Spray Concentration and Bioassay Cage Penetration Data1

Abstract

Field trials were conducted to demonstrate the need for correcting sampled spray concentration data for sampler collection efficiencies and estimated spray exposure levels in mosquito bioassays for cage interference effects. A large spray block was targeted with aerial spray treatments of etofenprox in order to create a gradient in both spray concentration and mortality. Spray concentrations were measured using rotary impactors, which were coupled with caged bioassays. Measured spray concentrations were corrected for sampler collection efficiencies, which ranged from 55% to 15%. The corrected spray concentrations were then used to estimate the spray levels inside the bioassay cages. Given the cage type used (Townzen type) and wind speeds occurring during the spray trials (2-4 m/sec), concentrations inside of the bioassay cage ranged from 65% to 68% of that measured within the spray block. Not correcting for the combination of sampler collection efficiency and cage interference, underestimated spray concentration levels inside the cages were 76-90%. Correcting field-measured data allows not only better comparisons between differing studies, but can also provide better estimates of caged insect mortality versus actual spray concentration exposure levels.