Characterizing and predicting sublethal shifts in mobility by multiple stored product insects over time to an old and novel contact insecticide in three key stored commodities

Authors: Morrison, William - Rob; Arthur, Franklin; Bruce, Alexander

Submitted to: Pest Management Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/13/2020
Publication Date: 3/15/2021
Citation: Morrison III, W.R., Arthur, F.H., Bruce, A.I. 2021. Characterizing and predicting sublethal shifts in mobility by multiple stored product insects over time to an old and novel contact insecticide in three key stored commodities. Pest Management Science. 77(4):1990-2006. https://doi.org/10.1002/ps.6228.
DOI: https://doi.org/10.1002/ps.6228

Interpretive Summary: There has been a push to diversify integrated pest management (IPM) programs away from exclusive fumigant in stored raw grains. Residual insecticides have been increasingly included among other chemical control techniques. Relatively few studies have comprehensively examined effects of residual insecticides on insects for those individuals that do not die; however, this is critical to determining the full efficacy of insecticides. Here, we evaluated the movement of four important stored product pests (red flour beetle, lesser grain borer, rice weevil, and maize weevil) in response to commodities (wheat, corn, and rice) containing aged insecticide residues of an existing insecticide (tradename: Diacon IGR+, with methoprene + deltamethrin) and novel (Gravista®, with methorene + deltamethrin + synergist) residual insecticide. Residues were aged at 3 month intervals from 0–12 months. We found that after exposure, movement was reduced by 50–88% and equally by adults exposed to each insecticide formulation compared to untreated controls. After initial application, predicted distance moved increased from 4 m to 14 m then 28 m in a 24 h period at 0, 3 and 12 months after application, respectively. Effectiveness of each insecticide at suppressing movement generally wore off by 9–12 month after application. Given the quick and dramatic increases in movement for surviving insects after initial application, our results suggest that sanitation programs in the post-harvest environment are extremely important and it may be beneficial to pair chemical control with attractants to prevent dispersal of affected insects to new areas of a facility.

Technical Abstract: There has been a push to diversify integrated pest management (IPM) programs away from exclusive fumigant use at food facilities. Residual insecticides have been increasingly included among other chemical control techniques. Historically in stored products, indirect toxicity has been neglected in favor of evaluating direct effects for chemical control measures, including mortality and knockdown. Here, we evaluated the movement ecology of Tribolium castaneum, Rhyzopertha dominica, Sitophilus oryzae, and Sitophilus zeamais in response to aged residues of an existing (Diacon IGR+ with methoprene + deltamethrin) and novel (Gravista® with methorene + deltamethrin + synergist) residual insecticide. Using the maximum labeled rate and two exposure times for each species, we assessed distance moved and velocity on wheat, rice, and corn. Assessments were made from commodity residues aged at three month intervals between 0–12 months. We found that after exposure, movement was reduced by 50–88% and equally by adults exposed to each insecticide formulation compared to untreated controls. After initial application, predicted distance moved increased from 4 m to 14 m then 28 m in a 24 h period at 3 and 12 months after application, respectively. Effectiveness of each insecticide at suppressing movement generally wore off by 9–12 month after application. Given the quick and dramatic increases in sublethal movement after initial application, our results suggest that sanitation programs in the post-harvest environment are extremely important and it may be beneficial to pair chemical control with attractants to prevent dispersal of affected insects to new areas of a facility.