The reliability of the empirical phenology model proposed by Nam et al. (2013) was tested using spring emergence data of Thecodiplosis japonensis Uchida et Inouye (Diptera: Cecidomyiidae) from 1986 to 2011 in Yeongcheon, Korea. First, the lower developmental threshold temperature (LDT) was estimated using spring emergence of T. japonensis and field temperatures. Then a degree-day model to predict spring emergence of T. japonensis was constructed, based on LDTs estimated from field observations and laboratory temperature-dependent development data. Based on field observations, the estimated LDT value for postdiapause development of T. japonensis was 6.1°C, only 0.2°C higher than that estimated from laboratory data. The explanatory power of the empirical degree-day model constructed on the basis of LDT from field observations was 87.2%, similar to the 87.0% of a degree-day model based on laboratory data, suggesting that both models had similar explanatory power. Furthermore, the predictions of median date of emergence in both models were only five days earlier than the observed median date in 2011. These results show that the empirical phenology model based on field observations is a reliable method for predicting the phenology of insects.