Spatial pattern in aerosol insecticide deposition inside a flour mill

Authors: Campbell, James - Jim; Arthur, Franklin; ZHU, KUN YAN - Kansas State University

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/26/2013
Publication Date: 2/7/2014
Publication URL: http://handle.nal.usda.gov/10113/58600
Citation: Campbell, J.F., Arthur, F.H., Zhu, K. 2014. Spatial pattern in aerosol insecticide deposition inside a flour mill. Journal of Economic Entomology. 107(1):440-454. DOI: http://dx.doi/org/10.1603/EC13423.

Interpretive Summary: Aerosol insecticides are applied as small droplets into the air, which then settle onto surfaces to provide control of stored-product insects inside food facilities such as mills and warehouses. Features inside a room such as mill and processing equipment, bins, columns and pallets of food are predicted to impact how these droplets disperse, creating zones within a room with lower droplet deposition and lower insect mortality. We used a high density grid of dishes containing confused flour beetle as a means to determine the amount of insecticide being deposited at a given location and developed a new efficacy index to show that two pyrethrin aerosols did exhibit zones with high and low efficacy within a flour mill. However, rather than the obvious physical barriers it tended to be along walls and in corners where lower efficacy occurred. The temperature when the aerosol was applied also impacted efficacy. A third insecticide, DDVP, that is an organophosphate and readily vaporizes and can cause mortality in the vapor phase was very consistent in causing insect mortality throughout the flour mill. We also used boxes of different heights and open on only one end to evaluate aerosol dispersal under a horizontal surface. Aerosol dispersal under the box decreased with decreasing box height and distance under the box in a way that could be quantified and used to predict where low efficacy is likely to occur within a food facility. These results show the potential for spatial variation in aerosol efficacy within a food facility and identify locations that are likely to receive lower dosages of insecticide and need supplemental treatment to maximize overall efficacy.

Technical Abstract: Aerosol insecticides are commonly used for management of stored-product pests inside food facilities, but the physical complexity of the interior of most food facilities may influence the dispersal and deposition of aerosol droplets and create spatial variation in efficacy. The spatial pattern in aerosol insecticide deposition was evaluated inside on multiple floors of a flour mill using a high density grid of bioassay dishes containing adult Tribolium confusum Jacquelin du Val. Three aerosols, Aerotech with NyGuard, Pyrocide 100 + Diacon II, and Vap20, were evaluated at normal (27 °C) and high (40 °C) target temperatures. For the two pyrethrins insecticides, Aerotech and Pyrocide, there was spatial variation to efficacy assessed using a newly developed efficacy index, which was relatively consistent among floors, but varied with aerosol formulation and temperature. Walls and corners, especially behind the direction of application, and the far corner of the room had zones of lower efficacy, while open areas in the center of the room had the highest efficacy. The organophosphate insecticide, Vap20, provided high efficacy at all locations, probably due in part to its vapor toxicity. Using boxes 1 m deep and 5, 10 or 20 cm high and open on only one end, the relationship between gap height and aerosol dispersal under horizontal surfaces was also determined using the efficacy index. These results show the potential for spatial variation in aerosol efficacy within a food facility and identify locations that are likely to receive lower dosages of insecticide and need supplemental treatment to maximize overall efficacy.