In the leaves, the larvae form linear mines, if space is available, confining frass to the sides in regular, alternate strips. If leaves are very small, the larvae form blotch mines. There are three larval stages. Pupation occurs within the leaf and lasts 7 to 11 days, depending upon the time of the year. Adults live 3 or4 weeks.
Partial generations occur in the winter when the reproductive activities of the insects decrease.
The flies can be found in greenhouses year-round. It is important to remove infested plant debris from the greenhouse to impede the populations of Liriomyza trifolii. At one time Liriomyza trifolii was a very difficult insect to control because it is highly resistant to many organo phospate, carbamate, and pyrethroid insecticides. With the in troduction of cyromazine and abamectin for leafminer man agement, the incidence of Liriomyza trifolii decreased dramatically. For specific chemical control recommendations, see your Cooperative Extension Service publications on ornamental plant pest management.