Aerosolize insecticide spray distributions and relationships to storage insect efficacies

Authors: Brabec, Daniel - Dan; LANKA, SRINIVAS - Kansas State University; Campbell, James - Jim; ARTHUR, FRANK - Retired ARS Employee; Scheff, Deanna; ZHU, KUN YAN - Kansas State University

Submitted to: Insects
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/8/2023
Publication Date: 11/28/2023
Citation: Brabec, D.L., Lanka, S., Campbell, J.F., Arthur, F., Scheff, D.S., Zhu, K. 2023. Aerosolize insecticide spray distributions and relationships to storage insect efficacies. Insects. 14(12. Article 914. https://doi.org/10.3390/insects14120914.
DOI: https://doi.org/10.3390/insects14120914

Interpretive Summary: Insecticides applied as aerosols (i.e., small droplets) are widely used in food facilities to manage insect infestations of raw grain and packaged products. These facilities are often large and complex spaces containing equipment and structural features that could affect the movement of insecticide droplets after release and cause variation in efficacy. The purpose of this study was to investigate the spatial variation in particle size distributions of two different insecticides when released at different locations within a pilot scale flour mill. The number and concentration of medium and large sized droplets that are generally most effective at controlling insects were determined and an estimate of deposition was calculated. There was spatial variation in insecticide deposition that was influenced by insecticide type and application method, application location, distance from release point and structural features in the facility. Measurements of aerosol insecticide droplet deposition were correlated with efficacy against the confused flour beetle as measured in an earlier study. For one insecticide formulation, insecticide efficacy against adults increased with increasing deposition values, but efficacy against larvae was high at all deposition values. For the second insecticide formulation, there was no relationship between insecticide deposition and efficacy against adults, but efficacy against larvae increased with increasing deposition. These findings indicate that the index developed to estimate deposition can be an effective tool for estimating insecticide efficacy, but relationship is impacted by the insecticide type and formulation. Results show how spatial variation in insecticide deposition can impact the level of insect control that is likely to result from an aerosol treatment, and identifies how changes in application location within a facility could improve consistency in deposition and ultimately improve impact of aerosol insecticide treatments.

Technical Abstract: Aerosol insecticides are widely used in stored product insect management programs in food facilities. Previous research has shown spatial variation in aerosol efficacy within facilities, but information on how spatial patterns of aerosol droplet concentration, size distribution, dispersal and deposition contribute to this variation in efficacy is limited. A study involving two aerosol formulations and application systems (TurboCide Py-75 with IGR (ChemTech Ltd., Des Moines, IA) and Pyrocide 100 (MGK, Minneapolis, MN) with Diacon II (Wellmark, Schaumburg, IL)) that were applied at single or multiple application points was conducted in a small-scale flour mill. The droplet size distributions were monitored at multiple locations within the mill room being treated using nine aerodynamic particle sizing (APS) instruments. The APS data collected over the treatment period was summarized into a mass concentration index (MCI), which ranged from 155-2549 mg/m3 for TurboCide and 235-5658 mg/m3 for Pyrocide. A second index, Dep.Idx, was derived to estimate potential insecticide droplet deposition on the floor and has units of g/m2. The Dep.Idx was below 5.3 g/m2 for most Turbocide applications. The Dep.Idx was below 8.4 g/m2 for most Pyrocide applications. The MCI and Dep.Idx values varied with APS location and application point, with proximity to the aerosol application location and degree of obstruction between release point and APS location contributing to this variation. Using efficacy data collected in an earlier studies, the relationship between aerosol droplet parameters and direct efficacy from pyrethrins on adults or IGR residual efficacy on larval development was assessed using Tribolium confusum Jacqueline DuVal. For TurboCide efficacy against adults increased with MCI and Dep.Idx values, but for residual efficacy of the IGR it was high at all aerosol droplet values so no relationship was apparent. In contrast, with Pyrocide there was highly variable efficacy against adults with no apparent relationship with aerosol MCI or Dep.Idx, but with residual IGR efficacy there were increasing negative effects on larval development with increasing MCI and Dep.Idx. Contour plots of Dep.Idx values were developed which could be used to predict areas of the mill that are not receiving an adequate application rate, and this could be used to develop more effective application strategies.