Pine sawflies were studied, because they infest needle leaves of pine trees in their larval stages, epecially Pinus kesiya which is widely cultivated in the mountains of the northern Thailand. The studies took place in the plantations and in the mixed natural forests in Chiang Mai. Five species of pine sawflies were found : Nesodiprion biremis, Diprion hutacharernae, Gilpinia marshalli, G. leksawasdii and G. paitooni. Four pine sawflies species were investigated on external morphology, two on infestation, all five on population. Parasitoids were also studied in relationships between the number of pine sawflies and parasitoids,

temperature, relative humidity and rainfall.