In the laboratory 90.7% of both sexes of moths of the pale western cutworm, Agrotis orthogonia Morrison, emerged from pupae between noon and midnight; almost half emerged between 2 and 4 p.m. Mating, evidenced by spermatophores in the bursa copulatrix, occurred almost always at night, within 3 days of emergence, and at temperatures between 5 and 35 °C. Most females mated only once. Multiple matings, with a maximum of 3 times, occurred in less than 20% of females. Males mated with a maximum of three females. Eggs developed during the pupal stage and were ready for fertilization when the moths emerged. Oviposition began on the first or second day after mating, peaked soon after, and continued until just prior to death of females. Maximum oviposition by one female was 564 eggs, with means from 90 to 342. Oviposition occurred at all temperatures from 5 to 35 °C. with an optimum between 10 and 25 °C. More eggs were laid in the dark or in subdued light than in continuous bright light. Females when unfed could oviposit but when fed water or sugar solutions they laid more eggs. Longevity varied directly with feeding and inversely with temperature. Mean longevity of moths fed honey solution in the laboratory was 12 days for both sexes. A diurnal rhythm of oviposition occurred with distinct peaks; 80% or more of the eggs were laid between noon and early evening. Rhythm of oviposition was apparently initiated by light and could be reversed by reciprocal light regimens but was maintained in continuous dark or light. The maximum distance flown on a flight mill was 14.7 miles for males and 3.5 miles for females. Speed varied from less than 1 to almost 3 m.p.h.