Ecology and Management of the Asiatic Garden Beetle, Maladera formosae, in Corn-Soybean Rotated Agroecosystems.

다국어 초록 (Multilingual Abstract)

The Asiatic garden beetle, Maladera formosae (Brenske) (syn. M. castanea [Arrow]), is an annual white grub species that was introduced to North America 100 years ago and quickly established as a pest of turf-grass, ornamentals, and vegetables in the Mid-Atlantic states. Over time, economic damage to these crops by M. formosae became merely sporadic, though its geographic range continued to expand. Now, in 2022, it is reported in at least 25 states and two Canadian provinces. Unexpectedly, in the last 15 years M. formosae emerged as a significant, early-season pest of field corn grown in sandy soils of the Great Lakes region. The beetle overwinters in the soil as a grub and in the spring second and third instars feed on seedling corn roots shortly after planting, causing stand loss that can exceed 40%. Management is difficult and many chemical products used against other annual white grub species are ineffective against M. formosae.Many questions surround the recent emergence of this near-endemic species as a corn pest nearly 100 years after its introduction, and we are hampered in its study by a lack of research techniques designed for use in field crops, and by a lack of understanding of its basic life history in the climate and habitats of this region of the country. The overall goal of this research was to investigate the ecology and management of M. formosae in corn-soybean rotated agricultural systems of the Great Lakes region.At the time M. formosae emerged as a pest in the Great Lakes region, most available literature stemmed from horticultural settings of New York and New Jersey in the 1930s. Scouting for M. formosae grubs is problematic as the grubs are subterranean and adults are nocturnal, and no standardized sampling methods have been developed for the species. To develop sampling methods for grubs in corn-soybean rotated fields, I first evaluated the compact cutter, cup cutter, and wire-mesh bait station. The cup cutter, which takes a smaller but deeper soil 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 efficient and economical since it can be used with less equipment in a single trip to the field. I then investigated sampling methods for the adults, since they are responsible for laying eggs that hatch into the grubs that overwinter and feed on corn roots the following spring. I performed two experiments: one to evaluate pitfall traps and sticky cards for sampling beetle emergence, and the other to evaluate milkjug traps and blacklight traps for sampling beetle flight. Pitfall traps were effective at capturing beetles, but not sticky cards. Peak abundance was observed between June 28 and July 5. Flying adults were strongly attracted to the blacklight trap, which caught nearly100-times more adults than the milkjug traps. These sampling tools are useful for researching the life history characteristics of M. formosae in field cropping systems.I then evaluated the life history characteristics of M. formosae in Michigan and Ohio corn-soybean rotated fields in 2018 and 2019. In Michigan and Ohio, about 40-50% and 25-30% of grubs emerging from overwintered grubs are second instar, respectively. Second instars were sampled as late as mid-June in Ohio and early July in Michigan. In both states most grubs emerged from overwintering in the third (and final) instar. Grub activity was detected in mid-April, peaked in May, and declined through June. Grubs were no longer sampled in Ohio by mid-June, but remained in the soil until July 1 in Michigan. Pupae in Michigan were first recovered one to two weeks later than in Ohio. Of the diet options typically available in a corn-soybean rotated field, grubs generally showed preference for ? and gained significant body mass when subjected to corn and marestail (a weed) but were also able to survive and develop on soybean, crop residues and bare soil. Grubs are also concentrated to soils with sand content exceeding 75%; relatively few grubs, if any, are sampled in loamy soils. In particular, grub distribution was most affected by sand and clay content, and soil moisture.I monitored adult ground movement and flight using pitfall traps and milk jug traps, respectively. Adult emergence out of the ground in Michigan occurred one to two weeks later than in Ohio. Adult movement around the soil surface peaked during the last week of June in Ohio and the first week of July in Michigan. In both states, ground movement significantly declined shortly after peak flight activity and never recovered. Adult capture rates also increased in soils with sand content exceeding 75%. Adult flight, which requires warm night temperatures around 20°C, peaked at the same time in early July in both states. Unlike ground movement, adult flight steadily declined throughout July into August. Beetle flight did not seem to be influenced by adjacent or surrounding habitat type. However, there were significantly more flying males than females during peak flight. The sex of beetles was determined from the orientation of the posterior abdominal sternite and pygidium, a newly reported sex-determination feature for M. formosae. Understanding the timing and duration of M. formosae life stages in corn-soybean rotated fields of the Great Lakes region will ultimately inform the timing and implementation of management strategies.Management of this pest is difficult in affected fields. Soil-applied and seed-applied insecticides are often used for management of soil-dwelling insects. However, M. formosae has been observed at high densities in fields planted with neonicotinoid-treated seed treatments and in-furrow pesticides. Entomopathogenic nematodes are a biological control agent used to manage M. formosae grubs in turfgrass. I examined their potential to control M. formosae in field corn. I isolated three species of naturally occurring entomopathogenic nematode, Heterorhabditis bacteriophora, H. megidis, and Steinernema glaseri, from infested fields in northern Ohio, and I confirmed their ability to infect and kill M. formosae grubs in greenhouse and microplot field trials. Relative to commercially available nematode isolates, locally isolated species are already preadapted to local environmental extremes and persist and suppress pest populations longer.Perhaps the most mysterious question surrounding the recent advent of M. formosae as a corn pest in the Great Lakes region is why, why corn, why here, why now? A first step in addressing these questions is to diagnose the population structure of M. formosae in this region relative to other regions. I conducted the first population genetics study on M. formosae populations sampled from three regions in the U.S.: Mid-Atlantic, New England, and the Great Lakes regions. Low genetic variation was detected among populations from different regions or habitats. However, only three genes were used to assess population structure. A genome-based approach with more intensive sampling is needed to gain higher resolution and determine if populations in the corn-pest region are genetically clustered. This knowledge could help predict the likelihood that M. formosae could become a significant pest of field corn in other areas.