Seasonal fluctuation in the occurrence, larval development, and gall formation of the rice gall midge in the wild rice (Oryza rufipogon) was examined throughout the year in northern Thailand. Larval population was much higher in the dry season than in the wet season. On the contrary, the number of galls was found to be more abundant in the wet season than in the dry season. A peak of larval population was recognized in the period from December to February with the minimum air temperature lower than 14°C. The 1st instar larvae were found to be very much abundant from November to January. The population of the 2nd or 3rd instar larvae showed two peaks, one in October and the other in February. Larval development is considered to be inhibited by low temperature and dry condition which also affect growth of the wild rice. It is evident that some of the rice gall midge can proceed from generation to generation in the wild rice throughout the year. Wild rice is the most important alternate host plant for the rice gall midge during the dry season.