|QUELLHORST, HANNAH - Kansas State University|
|SAKKA, MARIA - University Of Thessaly|
|GOURGOUTA, MARINA - University Of Thessaly|
|Morrison, William - Rob|
|ZHU, KUN YAN - Kansas State University|
|ATHANASSIOU, CHRISTOS - University Of Thessaly|
Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/26/2023
Publication Date: 6/1/2023
Citation: Quellhorst, H.E., Sakka, M., Gourgouta, M., Morrison Iii, W.R., Zhu, K., Athanassiou, C.G. 2023. Efficacy of deltamethrin and pirimiphos-methyl in layer-treated maize against the larger grain borer and the maize weevil. Journal of Economic Entomology. 116(3), 2023, 1017-1024. https://doi.org/10.1093/jee/toad072.
Interpretive Summary: Grain protectants are applied as grain is loaded into bins during bulk storage on and off-farm, and must be effective against a range of stored product insects. However, most of the time all the grain is treated, but it is possible that only a smaller layer (or amount) of grain needs to be treated to deliver the same desired control. Using less grain protectants or amount of insecticide active ingredient would help satisfy growing consumer demand for commodities with fewer insecticides. In this study, we evaluated the grain protectants deltamethrin and pirimiphos-methyl when applied to a whole batch of grain, the upper half, just one fourth, or only one-eighth of a column of corn and looked at how it affected larger grain borer and maize weevil, two important corn pests after harvest. Mortality was nearly 100% for larger grain for all treatments and insecticides, even when just an eighth of the grain was treated. Mortality was much higher for pirimiphos-methyl than deltamethrin across all treatments for maize weevil. Our work suggests we may be able to use much less insecticide and achieve the same control for larger grain borer and maize weevil (depending on compound) compared to treating a full column of grain. This should help decrease insecticide inputs after harvest.
Technical Abstract: Two grain surface treatment insecticides (deltamethrin and pirimiphos-methyl were evaluated in laboratory assays as a surface treatment for maize to control adult Prostephanus truncatus and Sitophilus zeamais. Both insecticides were applied to 20 g of maize placed in a vial or to the upper one half, one fourth, or one-eighth layer of the maize. Insects were either added to the vials before or after the maize. Mortality, progeny production, and insect damaged kernels (IDK) were then evaluated for each vial. Introduction method (before or after) did not have any impact on any of the variables. Mortality was nearly 100% for all treatments for both insecticides for P. truncatus. Subsequently, progeny production and the number of insect damaged kernels was very low or zero for P. truncatus. Mortality for S. zeamais remained low across layer treatments for deltamethrin. However, S. zeamais was easily controlled by primiphos-methyl. The results of this laboratory study show that while deltamethrin and pirimiphos-methyl has some effectiveness as a layer treatment on a column of maize, efficacy will be dependent on the target species, and the depth of the treated layer, as well as the location on which the insects are present.