The cutwormMeltpotis indomttaWalker is the most important defoliator of honey mesquite,Prosopts glandulosaTorrey var.glandulosa, in the southwestern United States. Several aspects of its population dynamics were investigated in the insectary and field at Temple, Tex., because of its potential value in a biological control program. Females deposited about 750 eggs, and a generation was completed in about 45 d in an insectary at natural temperature and photoperiod. Insectary populations increased 1.12 times per day and doubled every 6.3 d. In the field, larvae eclose from egg masses presumably deposited in crevices under mesquite bark, feed nocturnally on the leaves, and pupate in the soil. The highest level of cutworm activity was observed in 1980 on the Edwards Plateau where the population density in the soil beneath a heavily defoliated mesquite stand was 70.1 larvae and 15.6 pupae/m2. Light trap samples showed moths were active as early as mid-April in 1982 in central Texas. Adult emergence continued into October during 1981 and 1983, giving no indication thatM. indomttaunderwent a pupal diapause. Weather conditions and parasitism of larvae and pupae were important factors regulating populations ofM. indomtta. The potential effectiveness ofM. indomttaas a biological control agent of mesquite was also examined. It was concluded thatM. indomttawould be only a partially effective agent because the defoliating activity of the larvae does not permanently damage mesquite.