Temperature-dependent development of overwintering pupae of Phyllonorycter ringoniella and its spring emergence model

Asiatic apple leafminer, Phyllonorycter ringoniella (Matsumura), is an important insect pest of apple. Overwintering pupae were collected from the apple orchards on February 11, February 25, and March 15, 2016, respectively. The three cohorts were subjected to six constant temperatures (12.0, 15.0, 20.9, 26.1, 29.9, and 35.6 degrees C, RH 75 +/- 5%) and further development into adults was studied. The developmental period decreased with increasing temperature up to 29.9 degrees C and no development occurred at high temperature (35.6 degrees C). The development period was longest at 12.0 degrees C (56.44 +/- 2.72 days) and shortest at 29.9 degrees C (13.33 +/- 1.65 days) from the second sampling colony (February 25, 2016). Based on the linear relationship between developmental rates and temperatures, the lower developmental threshold (LT) and thermal constant (K) of overwintering pupae were estimated to 7.06 degrees C and 307.6 DD, respectively. The nonlinear Logan-6 model provided good description of temperature-dependent development especially with high temperature inhibition (r(2) = 0.99). The cumulative emergence of P. ringoniella from overwintering pupae was well described by the two-parameter Weibull function (r(2) = 0.83) using the accumulated degree-days based on the LT 7.06 degrees C. This model was validated with actual spring emergence data in both semi-field and field conditions in 2015 and 2016. The model would be useful in predicting the spring emergence of P. ringoniella and establishing management tactics against P. ringoniella in apple orchards.