A degree-day model for forecasting adult phenology of Popillia japonica (Coleoptera: Scarabaeidae) in a temperate climate

Abstract

Japanese beetle, Popillia japonica (Newman), was first detected in the United States in New Jersey in 1916. The beetle gradually spread to the Midwest U.S. region, and was first confirmed in Minnesota in the late 1960’s. Popillia japonica has subsequently become a major invasive insect pest in turfgrass and several agricultural crops. As P. japonica continues to spread throughout the U.S., and other countries, it is important to develop efficient ways to monitor adult populations, and where possible, forecast the phenology of adult population dynamics. During 2019-2021, field trials were conducted to develop a degree-day model that can be used to forecast P. japonica adult phenology under Minnesota, and Midwest summer climatic conditions in. We used commercially available traps and lures to monitor adult flight phenology, specifically beetle trap-catch, along with weather data at four locations in Minnesota, to relate ambient field temperatures to population phenology. The concordance correlation coefficient (CCC), an index of both precision and accuracy, was used to develop a final degree-day model. Model development included evaluation of simple and sine-wave degree-day calculation methods, start dates between 1 Jan. and 1 April, and a range of lower (0-15 °C) and upper (20-37 °C) thresholds. The optimum model was found to be a simple degree-day calculation, using a biofix date of 1 Jan, and lower and upper thresholds of 15 and 21.7 °C, respectively, for predicting 10% beetle trap-catch. The model will aid in future integrated pest management (IPM) and regulatory strategies by providing a tool for prediction of P. japonica adult flight phenology.

Potential distribution and spread of Japanese beetle in Washington State

“…We obtained physiological parameters from a previous Japanese beetle model that calculated a low development threshold (10°C), a growing degree requirement for the life cycle (525 DD), and cold (–15°C) and heat (34°C) tolerant temperatures (Kistner-Thomas 2019). We also used a low development threshold of 15°C following the recent degree day model (Ebbenga et al 2022). Our final physiological models were averaged based on these 2 low thresholds.…”

The establishment of the association between the Japanese beetle (Coleoptera: Scarabaeidae) and the parasitoid Istocheta aldrichi (Diptera: Tachinidae) in Québec, Canada

“…For each sampling period, % Em corresponds to the estimated cumulative emergence of Japanese beetles based on the degree-day model of Ebbenga et al . (2022; see Methods section for details). Max I.a.…”

“…For each location, total parasitism rates over the course of the season were calculated based on the total number of Japanese beetles trapped. Because we suspected that we missed some beetles in early and late season, we used the degree-day model of Ebbenga et al (2022) to estimate the proportion of unsampled Japanese beetles. For each location, we used the weather generator of BioSIM 11 (cfs.nrcan.gc.ca/projects/133) to estimate daily minimum and maximum air temperatures.…”

“…Temperatures for each location were estimated through distance-weighted interpolation using up to eight weather stations nearest to each of the sampling locations (Régnière and St-Amant 2007). For each sampling location and year, simple degree-day accumulations were calculated using a biofix date of 1 January and lower and upper thresholds of 15.0 and 21.7 °C, respectively (Ebbenga et al 2022). Accumulated degree days for each sampling date were then converted to the expected proportion of emerged Japanese beetles using Ebbenga et al's (2022) equation ( 1).…”

“…estimation, Adj. Tot I.a.total parasitism rate by I. aldrichi over the season, adjusted for missing Japanese beetle collections based on the degree-day model ofEbbenga et al (2022); Nnumber of Japanese beetles examined for parasitism estimation. ‡Date Max corresponds to earliest captures of Japanese beetles.…”