When the alfalfa blotch leafminer, Agromyza frontella (Rondani), was held in the laboratory at 20±1.1°C, 65±5% RH, and 24L:OD, an avg of 141 eggs/♀ were laid (11% sterile eggs), adult longevity averaged 3 wk, and the sex ratio was 1.2 ♀:1.0 ♂. Larval instar was determined by measuring the length of the cephalopharyngeal skeleton: the 1st instar averaged 0.1, the 2nd instar 0.2, and the 3rd instar 0.3 mm. At 20° C, time for each stage or instar was egg (6 days), 1st instar (1 day), 2nd instar (2 days), 3rd instar (4 days), and pupa (23 days). Total time required for development was 52 days at 16.7°, 36 days at 20°, 31 days at 22.8°, and 27 days at 25.6°C. Female flies fed by making perforations, “pinholes,” with their ovipositors, and lapping the plant juices. The avg number of such perforations made during a female lifespan was 3769, the equivalent of ca. 1.1 cm3 of alfalfa leaflet. The adult fly damaged laboratory alfalfa by feeding; leaflets dehisced when populations were very high. The larvae damaged the alfalfa leaflet by mining (0.64 cm2 avg area/mine); this too usually resulted in leaflet dehiscence ca. 2 wk after larvae exited from the leaflets to pupate in the soil.