Aerosol insecticide distribution inside a flour mill: Assessment using droplet measurements and bioassays

Authors: Arthur, Franklin; Campbell, James - Jim; Brabec, Daniel - Dan; DUCATTE, GERALD - Mri Global; DONALDSON, JOHN - Mri Global

Submitted to: Journal of Stored Products Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/12/2017
Publication Date: 7/1/2018
Citation: Arthur, F.H., Campbell, J.F., Brabec, D.L., Ducatte, G., Donaldson, J. 2018. Aerosol insecticide distribution inside a flour mill: Assessment using droplet measurements and bioassays. Journal of Stored Products Research. 77:26-33. https://doi.org/10.1016/j.jspr.2017.12.004.
DOI: https://doi.org/10.1016/j.jspr.2017.12.004

Interpretive Summary: Aerosol insecticides are increasingly being used by the milling industry as an alternative to the fumigant methyl bromide. However, there is little information on the effectiveness of these treatments, especially in regards to the size of the aerosol particles that are dispensed, their concentration, or how they are distributed during an application. In a pilot-scale flour mill study comparing two aerosol formulations, one dispensed from a liquid fogging machine and one dispensed from a cylinder, we found that in general, aerosol particle size, concentration, and deposition amount of both aerosol formulations decreased with increasing distance from where they were applied. Equipment and support beams in the mill obstructed aerosol dispersion and deposition. Using bioassay insects to evaluate efficacy of deposited aerosol droplets indicated that there was no recovery of adult confused flour beetles exposed to the cylinderized aerosol, but with the liquid fogger there was recovery with increasing distance from the aerosol release point. Results show that aerosols applied from a fixed position may not distribute evenly throughout a milling facility, and that improving distribution would have a beneficial effect on resulting control. Mill managers and service providers can utilize these results to improve their pest management programs for control of stored product insects inside milling and processing facilities.

Technical Abstract: The distribution of aerosol applications of pyrethrin+methoprene, generated from a mechanical fogger, and pyrethrin+pyriproxyfen, dispensed from a pressurized cylinder, were characterized inside a pilot-scale flour mill using measurements of particle size and concentration and effects on adult confused flour beetles, Tribolium confusum Jacqueline duVal, in bioassay arenas. Particle measurements were made using TSI Aerodynamic Particle Sizers (APS) units placed in an open straight line at distances of 4.3, 8.9, and 13.5 m from the aerosol release point (open configuration). Measurements were also made using a second configuration (termed obstructed), which was done by moving the APS unit at 8.9 m underneath a piece of equipment, and moving the APS unit at 13.5 m behind a support beam. The APS units provided extensive data on aerosol particle size dispensed during the test, mass concentration, actual number of particles dispensed, which were then used to quantify aerosol characteristics. Actual concentration and calculated deposition was about 4x greater for the pyrethrin+methoprene aerosol compared to the pyrethrin+pyriproxyfen aerosol. Concentration and calculated deposition of both aerosols decreased with increasing distance from the spray release point and when the APS units were in the obstructed configuration. However, bioassays of adult T. confusum showed no difference in recovery after exposure to either insecticide, but recovery did increase with increasing distance from the spray release point. Results from this field trial show how efficacy of aerosol applications is impacted by distance and obstacles, how use of equipment that measures droplet size and concentration can help quantify the dispersion and spread of insecticidal aerosols. Results also provide guidance to develop relationships between aerosol deposition and efficacy and thus improve pest management programs for structural management of stored product insects.