The dispersal capacity of the invasive larger grain borer and the cosmopolitan maize weevil after brief exposure to a novel insecticide formulation

Authors: QUELLHORST, HANNAH - Kansas State University; ARTHUR, FRANK - US Department Of Agriculture (USDA); ZHU, KUN YAN - Kansas State University; BRUCE, ALEX - University Of Tennessee; Morrison, William - Rob

Submitted to: Journal of Stored Products Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/27/2023
Publication Date: 5/13/2023
Citation: Quellhorst, H.E., Arthur, F.H., Zhu, K., Bruce, A., Morrison III, W.R. 2023. The dispersal capacity of the invasive larger grain borer and the cosmopolitan maize weevil after brief exposure to a novel insecticide formulation. Journal of Stored Products Research. 102. Article 102125. https://doi.org/10.1016/j.jspr.2023.102125.
DOI: https://doi.org/10.1016/j.jspr.2023.102125

Interpretive Summary: The maize weevil and larger grain borer are global and invasive pests of stored maize, respectively. With the reduction in availability of fumigants, due to phase-out because of negative impacts on the ozone layer or the development of resistance, there is a need for new chemical tools for managing stored product insects. In addition to insecticide impacts on mortality, they can also reduce insect mobility leading to reduced colonization and product infestation. Here, we compare the ability of two insecticide formulations to inhibit long-distance movement of these two stored product insects. The dispersal capacity for larger grain borer, measured as the percentage of adults that were able to disperse to a food source, was reduced by 90–97% after exposure to either insecticide formulation compared to the control. By contrast, the dispersal of maize weevil to the food source was only reduced by 5–25% after exposure to either insecticide formulation compared to the control. A novel insecticide formulation (methoprene + deltamethrin + piperonyl butoxide) and an older formulation (methoprene + deltamethrin) that contains fewer active ingredients in higher concentrations than the new insecticide did not differ in their effects on either stored product species. Overall, our study highlights that insecticides can have a significant impact on movement for some species of stored product insects, which may prevent colonization of food sources and reduce population levels. However, the movement of some species remains less impacted, which warrants further investigation.

Technical Abstract: The larger grain borer (Prostephanus truncatus) and the maize weevil (Sitophilus zeamais) are major pests of stored maize. With the phase-out of methyl bromide, our most effective fumigant after harvest, and increasing resistance to phosphine, the most commonly used fumigant, there is a need for alternative management tactics. Here, we present a more realistic test of the effectiveness of a novel insecticide formulation (methoprene + deltamethrin + piperonyl butoxide; tradename, Gravista ') compared to an older formulation (methoprene + deltamethrin; tradename, Diacon IGR+') at reducing the horizontal dispersal capacity to food patches by both of these stored product species. To do this, we used a dispersal apparatus (consisting of 30 or 70 cm PVC pipe modified with a baited pitfall trap at one end) where we introduced cohorts of adults after exposure on concrete arenas at labeled rates and gave them 48 h to disperse to a novel food source consisting of 15 g of maize. The dispersal capacity for P. truncatus, measured as the percentage of adults dispersing to the novel food source, was significantly reduced by 90–97% after exposure to Gravista or Diacon IGR+ compared to the control. By contrast, the dispersal capacity for S. zeamais was only reduced by 5–25% after exposure to either insecticide formulation compared to the control. Both formulations worked equally well for each species, but general suppression was lacking for S. zeamais. Overall, our study highlights the importance of using realistic behavioral assays in comprehensive insecticide testing to provide a full picture of insecticide efficacy.