Degree-day forecasing of generation time of Cydia pomonella (Lepidoptera: Tortricidae) populations in California
1992
Pitcairn, M.J. | Zalom, F.G. | Rice, R.E.
The generation time of Cydia pomonella (L.), measured as the number of degree-days occurring from the start of a flight to the start of the following flight, was estimated for 176 generations in walnuts, apples, pears, and other hosts at several locations throughout California. The results show that the accumulated number of degree-days during the first generation (average, 595.62 DD [>1O degrees C]) was significantly lower than the number of degree-days for the second and third generations (average, 677.68 and 685.06 DD [>10 degrees C], respectively). There was no significant difference among hosts within flights, but significant differences did exist among locations. Five published degree-day models were compared using the data set. Model accuracy, reported as root mean square error (RMSE), ranged from 6.3 to 10.8 d across generations. A degree-day model using 1O degrees C as the lower threshold, 31.1 degrees C as the upper threshold (horizontal cutoff), and a generation time of 619 DD provided an adequate fit to the data when all generations were considered. The median predicted duration of the first generation was 4 d too long; however, 72% of the predictions were within approximately 7 d of their observed date. The median predicted duration of the second generation was 2 d too short; however, 82% of the predictions were within approximately 7 d of their observed date.
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