Using thermal time to predict the timing of flight activity in Noctuidae (Lepidoptera) species: Calculation and verification of forecast methods

From 1967 to 1995, the flight activity of 25 monovoltine species of moths (Noctuidae, Lepidoptera) was monitored via a light trap located in Prague (50.09 N, 14.30 E). For each species, the day when half of the individuals were caught (peak of flight activity, PFA) was specified each year. This study addresses a method of predicting the calendar date of the PFA via thermal time. We determined a base temperature of +6 C, at which the differences between the predicted and actual dates of the PFA were minimal. For each species and each year, the sum of the degree days exceeding the base temperature from January 1 to the date of the PFA (SumT) was determined, and the average SumT throughout the study was calculated. Each year, the predicted date of the PFA is the date when the average SumT was achieved. Sixty-five percent of the predicted PFA dates fell within ±5 days of the actual date of the PFA. Shifts in the magnitude and direction of the difference between the actual and predicted PFAs affecting concurrently all species were caused by the thermal conditions of the year.