Experience can induce oviposition on nonhost plants, but little is known about the mechanisms underlying such behavioral changes. In laboratory experiments, we examined the effects of early adult experience of nonhost volatiles and larval food restriction on the olfactory response and oviposition preference of the diamondback moth, Plutella xylostella, a specialist herbivore of cruciferous plants. Naïve ovipositing females showed aversion to the odor of pea, a nonhost plant of P. xylostella, and seldom accepted pea plants for oviposition. However, females with prior experience with pea odor showed preference for the volatiles and significantly increased acceptance of pea plants for oviposition. Larval food restriction did not alter olfactory response and oviposition preference. We conclude that olfactory learning plays a significant role in inducing oviposition on nonhost plants and may contribute to host range expansion in phytophagous insects.