In laboratory experiments at 21–22°C, nearly 100%Stethorus picipesCasey ♀ oviposited when reared and held as adults at a 16-h photoperiod, continuous light or continuous darkness. Only ca. 30% oviposited when reared and held as adults at a 10-h photoperiod. The reproductive-nonreproductive state of females was demonstrated as reversible by exposure to appropriate photoperiods. The results of the experiments are discussed in reference to natural populations in southern California. Mean egg production and longevity were 577 eggs and 130 days at 16-h photoperiod and 21–22°C. Oviposition response showed that eggs and larvae ofTetranychus pacificusMcGregor were more favorable as food than other stages of prey.