A combination of parasites and compatible insecticide applications can keep leafminers in check and delay the development of resistance.

Drs. I. P. Ting and L. Bates, Department of Botany and Plant Sciences, UC Riverside, provided information on the proper use of the porometer as well as access to the syntillation counter. The author gratefully acknowledges the help of H. Nakakihara, W. Carson, J. Feaster, T. Perring, and J. Morse. This research was supported in part by grants from the California Celery Advisory Board.