Forecasting the beetle storm: Abiotic drivers of Japanese beetle phenology and abundance in Midwestern vineyards

The invasive Japanese beetle (Popillia japonica, Coleoptera: Scarabaeidae) is an
expanding pest in the US, causing millions of dollars in annual damage to crops, turf, and
ornamentals. In Wisconsin, adult beetles are the primary defoliator of grapes. Larvae develop in
the soil feeding on turf grass roots, and their distribution, development timing, and influence
on adult populations in vineyards remain difficult to predict. Adult beetles are highly mobile
and fly several miles in search of suitable food and abiotic conditions, further complicating
population forecasts. Accurate predictions of both larval and adult populations are essential for
improving pest managements strategies of this important pest.
Several abiotic factors – including temperature, moisture, and surrounding landscape
characteristics – may influence beetle phenology and abundance. While previous models have
successfully predicted Japanese beetle phenology with air temperature, they often overlook soil
characteristics which more directly reflect larval conditions and may better predict phenology
than air characteristics alone. This study tracks soil temperature, soil moisture, and air
temperature in vineyards across Wisconsin and one site in Minnesota to predict adult
emergence timing in the spring.
Additionally, although research has shown that landscape composition influences adult
beetle distribution, it did not distinguish between cropping types. Crops such as
soybean are known to attract adults and cause population spillover into nearby areas. This
study incorporates fine-scale landscape distinctions to better predict adult population
abundance and distribution throughout the summer. These findings enhance our
understanding of Japanese beetle ecology and support more targeted pest management in vineyard
systems.