A forecasting model for the adult emergence of overwintered Monochamus alternatus (Coleoptera: Cerambycidae) larvae based on degree-days in Korea

Abstract

Emergence data from 1999 to 2011 were analyzed to develop a forecasting model of the adult emergence of overwintered Monochamus alternatus Hope (Coleoptera: Cerambycidae) larvae. The cumulative emergence curves of M. alternatus adults showed high variation year to year and were fitted by the Weibull function to obtain an all-combined preliminary model that was then used to separate fractional models. The emergence curves were grouped into three fractional modes—advance, regular, and delay—based on the number of discrepant days between actual and predicted date by the preliminary model at 50 % emergence date (predicted − observed), resulting in the mean number of discrepant days of 8.7, −0.2, and −8.0, respectively. Three assumptions were made to support the grouping: delay mode is selected when the third instars prevails in overwintering stages; advance mode is selected when the fourth instars prevail, since fourth instars immediately can go into pupal stage; regular mode is located between advance and delay mode. These three modes produced a 340, 420, and 500 degree-days (DDs) at 50 % emergence date, respectively, when each was fitted by the Weibull function, with DDs based on 11.9 °C from 1 January. The emergence models developed in this study considerably described the actual population phenology of M. alternatus, with the selection of advance, regular, and delay modes. Consequently, the models should be useful in establishing management strategies against M. alternatus in Korean forests.