Laboratory evaluation of particle size, food contamination, and residual efficacy of pyrethrin + methoprene aerosol

Authors: Arthur, Franklin; Campbell, James - Jim; DONALDSON, J - Mri Global

Submitted to: Journal of Stored Products Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/6/2017
Publication Date: 4/22/2017
Publication URL: http://handle.nal.usda.gov/10113/5666760
Citation: Arthur, F.H., Campbell, J.F., Donaldson, J.E. 2017. Laboratory evaluation of particle size, food contamination, and residual efficacy of pyrethrin + methoprene aerosol. Journal of Stored Products Research. 72:100-110. https://doi.org/10.1016/j.jspr.2017.04.003.
DOI: https://doi.org/10.1016/j.jspr.2017.04.003

Interpretive Summary: Aerosols containing insect growth regulators, which prevent immature insects from developing to the adult stage, are used to manage insect pest populations in flour mills. However, there is little information on how aerosols are deposited on a treated surface when they are applied at different particle sizes. We conducted several studies to determine effectiveness of an aerosol containing the insect growth regulator methoprene, by applying the aerosol at either 2 or 16 microns and exposing larvae of selected stored product insects. The aerosol applied at 16 microns was more effective, as measured by the number of larvae that could develop to the adult stage, apparently because of greater deposition of the larger particles. When food material was allowed be on the surface when it was treated or to accumulate on a surface, the food material resulted in greatly decreased effectiveness of the aerosol. Results show that when aerosols are used in flour mills and warehouses, the particles generated must be of a size sufficient to allow for deposition on the floor of the structure. In addition, any food material present will greatly reduce the effectiveness of that aerosol. Mill managers can use these results to better utilize insecticidal aerosols in management programs, especially by improving cleaning and sanitation.

Technical Abstract: A series of tests were conducted to determine residual efficacy of pyrethrin+methoprene aerosol to manage larvae of selected stored product insects. Efficacy was assessed through emergence of morphologically-normal adults and through a quantitative developmental index with values ranging from 1, for no advancement out of the larval stage, to 5, with advancement to the adult stage without deformities. Concrete arenas were treated with the aerosol droplets averaging 2µm or 16µm, food material placed on the arenas at 1-8 weeks post-treatment, and larvae placed on the arenas at the same time. No Lasioderma serricorne (DeGeer) larvae reached the adult stage at either particle size, though they developed further (i.e., developmental index values were higher) for 2µm compared to 16µm. No larvae of either Tribolium confusum Jacqueline duVal or Trogoderma variabile (Ballion) reached the adult stage when exposed to 16µm, but at 2µm most larvae completed development to the adult stage and index values were high. Exposed Dermestes maculatus (DeGeer) larvae completed development to the adult stage at both particle sizes, indicating low susceptibility to methoprene residues. In a second experiment, when food material in the arenas was also treated with two particle sizes and bioassays conducted in the same manner using only L. serricorne, T. confusum, and T. variable, results were similar to those described above. In the final experiment, only the 16µm particle size aerosol was used to treat arenas with or without food, with arenas without food having it added one day after treatment. At 1-8 weeks post-treatment, the food was transferred to new untreated arenas and food was replaced in the arenas originally treated with aerosol. Bioassays were conducted on all four types of arenas using only larvae of T. confusum and T. variabile. The food material blocked deposition of the aerosol on the arenas or absorbed some of the residues, leading to increased adult emergence and higher index values on the original treated arenas. Larvae exposed on the food material transferred from those arenas failed to emerge as adults, indicating transference of the methoprene residues from surfaces onto the food. Results show deposition on the arenas was greater at 16µm compared to 2µm, but residual efficacy was mitigated by the presence of food material.