Active and passive sampling methods for grubs of the Asiatic garden beetle, Maladera formosae (Coleoptera: Scarabaeidae), in a corn-soybean rotation

Abstract

Beginning in the mid-2000s, grubs of the Asiatic garden beetle, Maladera formosae (Brenske) (syn. M. castanea [Arrow]), emerged as significant early-season pests of field corn grown in sandy soils of the Great Lakes region. Overwintered grubs move towards the soil surface in springtime to resume feeding on roots, causing stand losses of up to 40%. Scouting for M. formosae is problematic as the grubs are subterranean, and the adults are nocturnal. The objective of this study was to evaluate sampling methods currently in use for other annual white grub species specifically for use with M. formosae grubs in corn production systems. In a series of two experiments, we evaluated the ability of the compact cutter, golf hole cup cutter, and wire-mesh bait station to detect M. formosae grubs and sense varying population densities. The cup cutter, which takes a deeper but smaller soil volume sample than the compact cutter, sampled more grubs per soil volume and was more sensitive to smaller grub populations. The bait station, a passive sampling technique, and cup cutter were both successful at detecting M. formosae before planting. However, the cup cutter is more adequate and economical since it can be used with less equipment in a single trip to the field. Identification of a standardized sampling methods will enable researchers to predict future infestations and ultimately lead to the development of economic threshold levels for M. formosae in row crop agroecosystems.