none Life history and natural enemies of an undescribed species of Pontania sawfly forming leaf galls on the arroyo willow, Salix lasiolepis Bentham, were studied at Flagstaff (Arizona, USA) from 1980 to 1984. Adults were morphologically indistinguishable from Pontania pacifica Marlatt, but galls, life history, and gall growth patterns were different, suggesting that the Pontania leaf-galler in Arizona is an undescribed species near P. pacifica that occurs on the same host plant. Arizona Pontania prepupae overwintered in cocoons in soil and adults emerged to oviposit into young willow leaves in July and August. Larval development was completed in ca. 9 weeks, and larvae emerged from galls in September and October. Adult oviposition behavior and development of immature stages and galls are described. Proportion of larvae surviving per generation varied from 8 to 23% from 1981 to 1983. From 55 to 79% of the sawflies died in the egg or early instars from abortion, unknown causes, and attack by two inquilines, Eurytoma fossae Bugbee and Batrachedra striolata Zeller. Ectoparasitoids, Bracon angelesius Provancher and Pteromalus sp., attacked later instars and killed 13-26% of the sawflies. Endoparasitoids were not found. Sawfly gall densities declined dramatically from an average of 56.4 galls per 100 leaves in 1980 to 3.1 in 1983.