Eliminating explanations for Maladera formosae (Coleoptera: Scarabaeidae) preponderance in sandy soil

Authors: Pekarcik, Adrian; Ranger, Christopher; LONG, ELIZABETH - Purdue University; TILMON, KELLEY - The Ohio State University

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/10/2024
Publication Date: 6/27/2024
Citation: Pekarcik, A.J., Ranger, C.M., Long, E.Y., Tilmon, K.J. 2024. Eliminating explanations for Maladera formosae (Coleoptera: Scarabaeidae) preponderance in sandy soil. Journal of Economic Entomology. Article toae138. https://doi.org/10.1093/jee/toae138.
DOI: https://doi.org/10.1093/jee/toae138

Interpretive Summary: Most field corn in the United States receives neonicotinoid seed treatment for the management of early-season, soil-dwelling insect pests. The insecticide is applied to the corn seed, taken up by developing roots, and translocated throughout the plant tissues; any insect feeding on the plant will ingest the insecticide. Larvae of the Asiatic garden beetle, Maladera formosae (Brenske), are white grubs that have been reported feeding on young field corn plants receiving neonicotinoid seed treatments in northwest Ohio, northern Indiana, and southern Michigan. Anecdotally, these infestations are seemingly restricted to sandy soils in the region. The purpose of this study was to 1) verify whether M. formosae populations in corn are restricted to sandy soils, and 2) determine whether soil type affects insecticide uptake by the plant, possibly explaining the observed differences in M. formosae abundance by soil type. First, we sampled grubs over time from two different soil types present in a single corn field and observed nearly 10-times more grubs in sandy than loamy soil. We then compared the concentrations of neonicotinoid insecticide seed treatment in the roots and shoots of corn seedlings grown in either sand or loam soil types over time. Similar amounts of the active ingredient were found in the roots and shoots of corn grown in both soil types. Within two weeks, the clothianidin concentrations in both soil types had significantly declined in roots and shoots and were no different from the no-insecticide control. These findings suggest that factors other than insecticide exposure contribute to the higher abundance of M. formosae larvae in sand as compared to loam soils, even within the same field.

Technical Abstract: Most field corn in the United States receives neonicotinoid seed treatment for the management of early-season, soil-dwelling insect pests. Larvae of the Asiatic garden beetle, Maladera formosae (Brenske), are annual white grubs that have been reported feeding on young field corn with both low and high rates of neonicotinoid seed treatments in northwest Ohio, northern Indiana, and southern Michigan. Anecdotally, these infestations are seemingly restricted to sandy soils in the region. The purpose of this study was to 1) verify whether M. formosae populations in corn are restricted to sandy soils, and 2) determine whether soil type affects insecticide uptake by the plant, possibly explaining the observed differences in M. formosae abundance by soil type. First, we sampled grubs over time from different soil types present in a single corn field and observed nearly 10-times more grubs in loamy sand than sandy loam soil. We then compared the concentrations of neonicotinoid insecticide seed treatment in the roots and shoots of corn seedlings grown in either sand or loam soil types over time. Similar amounts of the active ingredient were found in the roots and shoots of corn grown in both soil types. Within two weeks, the clothianidin concentrations in both soil types had significantly declined in roots and shoots and were no different from the no-insecticide control. These findings suggest that factors other than insecticide exposure contribute to the higher abundance of M. formosae larvae in sand as compared to loam soils, even within the same field.