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Title: Correction of spray concentration and bioassay cage penetration data

Author
item Fritz, Bradley - Brad
item Hoffmann, Wesley
item BONDS, JANE - Bonds Consulting Group
item HAAS, KEITH - Central Life Sciences

Submitted to: American Mosquito Control Association
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/1/2012
Publication Date: 12/1/2012
Citation: Fritz, B.K., Hoffmann, W.C., Bonds, J., Haas, K. 2012. Correction of spray concentration and bioassay cage penetration data. American Mosquito Control Association. 28(40):320-322.

Interpretive Summary: Field trials are a common method used to compare or test the effectiveness of different vector control spray application technologies. Measurements of spray concentration and caged insect mortality are typically collected at various locations within a designated treatment area to determine the spray dispersion and the degree of pest control. Tools used to measure both spray concentration and caged insect mortality have an inherent bias as a result of their interaction with the spray droplets, however these issues have been addressed for a number of spray concentration measurement devices and bioassay cages in several previous studies. Addressing both of these issues by applying the information developed in previous studies, the results of this study demonstrate that spray concentration levels inside the cages were underestimated by 76 to 90%. Developing a unified approach to correct field measurements for biases in droplet samplers and bioassay cages will yield meaningful estimates of dosages delivered to caged insects, and will help researchers more precisely target spray applications for maximum efficacy.

Technical 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 5-15%. The corrected spray concentrations were then used to estimate the spray levels inside the bioassay cages. Given the cage type used and wind speeds occurring during the spray trials, 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 from 76 to 90%.