Filtration effects due to bioassay cage design and screen type.

The use of bioassay cages in the efficacy assessment of pesticides, application techniques, and technologies is common practice using numerous cage designs, which vary in both shape and size as well as type of mesh. The objective of this work was to examine various cage shapes and mesh types for their filtration effects on air speed, spray droplet size, and spray volume. Reductions in wind speed and droplet size seen inside the cages were measured by placing cages in a low-speed wind tunnel at air speeds of 0.5 m/sec, 1 m/sec, 2 m/sec, and 4 m/sec and cage face orientations (relative to the air stream) of 0 degrees, 10 degrees, 22.5 degrees, and 45 degrees. Reduction in spray volume inside a select number of cages was also evaluated under similar conditions. Generally, greater air speed reductions were seen at lower external air speeds with overall reductions ranging from 30% to 88%, depending on cage type and tunnel air speed. Cages constructed with screens of lower porosities and smaller cylindrical-shaped cages tended to provide greater resistance to air flow and spray volume. Overall, spray droplet size inside the cages was minimally reduced by 0-10%. There was a 32-100% reduction in concentration of the spray volume applied relative to that recovered inside the bioassay cages, depending on the cage geometry and screening material used. In general, concentration reductions were greatest at lower air speeds and for cages with lower porosity screens. As a result of this work, field researchers involved in assessing the efficacy of vector control applications will have a better understanding of the air speed and spray volume entering insect bioassay cages, relative to the amount applied, resulting in better recommended application techniques and dosage levels.