Exposure to a reduced-risk insecticide on maize and concrete reduces movement by the stored product pests, Prostephanus truncatus Horn and Sitophilus zeamais Motschulsky

Authors: QUELLHORST, HANNAH - Kansas State University; Arthur, Franklin; BRUCE, ALEXANDER - University Of Tennessee; ZHU, KUN YAN - Kansas State University; Morrison, William - Rob

Submitted to: Frontiers in Agronomy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/28/2022
Publication Date: 3/24/2022
Citation: Quellhorst, H.E., Arthur, F.H., Bruce, A., Zhu, K., Morrison Iii, W.R. 2022. Exposure to a reduced-risk insecticide on maize and concrete reduces movement by the stored product pests, Prostephanus truncatus Horn and Sitophilus zeamais Motschulsky. Frontiers in Agronomy. 4:868509. https://doi.org/10.3389/fagro.2022.868509.
DOI: https://doi.org/10.3389/fagro.2022.868509

Interpretive Summary: Two major stored products pests of maize are the larger grain borer and maize weevil. Maize weevil is already established in the United States (US); however, larger grain borer is not frequently reported. Under climate change scenarios, larger grain borer is expected to become a biosecurity threat and may shift its distribution northward further into the US. Thus, there is a critical need to develop diversified chemical control tools in the post-harvest supply chain for these two species. In this study, we compared the efficacy of a new reduced-risk insecticide, Gravista®, which contains three active ingredients and the synergist piperonyl butoxide (Central Life Science, Schaumberg, IL, US), to Diacon IGR+®, an existing commercial formulation that contains the same active ingredients, but without the synergist. Insects were exposed to both insecticides applied to either treated concrete to simulate application to concrete flooring found in many food facilities or to maize to simulate application as a grain protectant. Direct mortality was recorded. In addition, insecticide exposure may also limit mobility and ability to colonize commodities, so impacts on movement were also assessed. The new formulation containing the synergist was as effective at inducing mortality and limiting mobility of both insect species on concrete and on maize as the commercial formulation; however, the new formulation contains lower concentrations of the active ingredients, thus making it a more cost-effective alternative that also may help reduce the emergence of insecticide resistant populations in the field. Overall, this new reduced-risk insecticide is a promising tool for controlling both species in bulk storage and around food facilities.

Technical Abstract: Two major stored products pests of maize are the Prostephanus truncatus Horn (larger grain borer) and Sitophilus zeamais Motschulsky (maize weevil). Under climate change, P. truncatus may be expected to shift its distribution northward further into the United States (US). Thus, there is a critical need to develop diversified chemical control tools in the post-harvest supply chain for these two species. In this study, we investigated the efficacy of a new reduced-risk insecticide Gravista®), containing the insect growth regulator, methoprene, combined with the pyrethroid, deltamethrin and the synergist piperonyl butoxide (Central Life Science, Schaumberg, IL, US), compared to the existing commercial standard formulation without synergist (Diacon IGR+®), and controls at inducing direct mortality and sublethal changes in movement on treated grains as a grain protectant, and on concrete as a surface treatment. Mortality of adults was assessed visually, while movement was tracked with a network camera coupled with Ethovision software that automatically recorded velocity and distance moved by both species, after continuous exposure on treated material for 4–168 h. The novel formulation significantly induced mortality while reducing distance and velocity moved by multiple-fold compared to controls for exposed adults even after relatively brief exposure periods. In fact, the novel formulation was just as effective as the older formulation, but used only a fraction of the active ingredients, thus it may be more cost-effective. Overall, the novel reduced-risk insecticide is a promising tool for controlling S. zeamais and P. truncatus in bulk storage and around other food facilities.