Abstract
In the spring generation, considerable difference of the larval development was found between two regional stocks. The progenies from the three-generation area developed rapidly and those from the two-generation area slowly. In the cross between two regional stocks, the larval development in the hybrid generations varied widely, but it resembled to that of the maternal parent. The three-generation stock persisted its inherent characters over the experimental period of 3 years after being transferred into the two-generation area. From these results the existence of the two distinct geographical ecotypes in the rice stem maggot was discussed.
