Effects of harsh climate on wild Japanese beetle populations

The Japanese beetle is an invasive species introduced to the United States from Japan in 1916.  Since then, the beetle has spread to cover most of the Eastern U.S., parts of the Midwest, and Midsouth. The annual densities of Japanese beetle adults and larvae were monitored from 2005 to 2012 and compared to climactic data. With few microbial and parasitoid natural enemies of P. japonica in the region, fluctuations of Japanese beetle populations is likely due to abiotic factors, such as severe spring flooding and extreme summer drought and heat waves along this invasive species’ southwestern border. Additionally, we used archival data on the range of temperatures the beetle can survive at, field collected data, and established soil thermal models, a predictive model for temperature dependent mortality of first and second instar was constructed. Data collected on first instar mortality showed from 2009 to 2012 fell within our predicted mortality ranges. Mortality of first instars molting into second instars was higher than the predicted range. This model may help explain the decrease in larval population densities of P. japonica with decreasing latitude as well as season collapses in populations during extremely hot summers and autumns.