Evaluation of residual efficacy of pyrethrin + methoprene aerosol on two dermestids: Impact of particle size, species and temperature

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

Submitted to: Insects
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/14/2019
Publication Date: 5/17/2019
Citation: Lanka, S.K., Arthur, F.H., Campbell, J.F., Zhu, K. 2019. Evaluation of residual efficacy of pyrethrin + methoprene aerosol on two dermestids: Impact of particle size, species and temperature. Insects. 10(5):E142. https://doi.org/10.3390/insects10050142.
DOI: https://doi.org/10.3390/insects10050142

Interpretive Summary: Insects of the family Dermestidae, including the warehouse beetle and the larger cabinet beetle, are becoming more prevalent pests in mills and warehouses where processed grain products are manufactured and stored. Aerosol treatments using reduced risk insecticides are becoming a more frequent treatment in food facilities, and they are often applied as a combination of pyrethrin and an insect growth regulator. These applications are used to treat surfaces and can have residual activity over multiple weeks after application, although environmental conditions may negatively impact this residual activity. There is comparatively little data on susceptibility of larvae of dermestid beetles to insecticides when applied in an aerosol formulation. When surfaces were treated with a combination of a pyrethrin and an insect growth regulator (methoprene) applied as an aerosol at two different average droplet sizes (4 and 16 microns) and then held at different temperatures, we found that the temperature at which the arenas were held had no effect on efficacy. However, larvae of the warehouse beetle were much more susceptible to the aerosol treatment compared to larvae of the larger cabinet beetle, and treating surfaces with the larger droplet size was much more effective then the smaller size droplets. Efficacy also declined with time. Results show that the particle size at which aerosols are dispensed is a critical factor for control, and that effectiveness of treatment will vary between species, thus identification of specific Dermestid species is important in developing management programs. Pest management professionals can use these results to more effectively control dermestids when they are encountered in mills and processing facilities.

Technical Abstract: Residual effects of pyrethrin + methroprene aerosol dispensed at 4 and 16-µm particle sizes, and an untreated control, was assessed against late-stage larvae of Trogoderma inclusum (LeConte), the larger cabinet beetle, and T. variabile (Ballion), the warehouse beetle. Treated arenas were stored at 25, 30, 35 and 40 deg C and bioassays were conducted at 1, 3, or 6 weeks post-treatment. Larval development was monitored through adult emergence to compare the efficacy of treatments by using both the percentage of normal adult emergence and a developmental index as dependent variables. There was no overall effect of temperature on residual activity as measured using either adult emergence or developmental index values. Both the 4 and 16-µm particle sizes resulted in reduced adult emergence and low developmental index values compared to untreated controls. The insecticide was more effective on T. variabile than on T. inclusum. The impact of particle size varied between species, both particle sizes reduced adult emergence and developmental index in T. variabile, but only the 16-µm particle size resulted in reduction of adult emergence of T. inclusum. Furthermore, there was a reduction in activity of methoprene with residual exposure time. The variations in susceptibility of species to methoprene, differences in efficacy of particle sizes and decrease in residual persistence at smaller particle sizes highlight the need for attaining optimal particle size to improve overall efficacy of aerosol mixtures containing methoprene.