The diamondback moth, Plutella xylostella (L.), is considered oligophagous on Brassicaceae. We determined the preference and performance of P. xylostella on canola, Brassica napus L., and flixweed, Descurainia sophia (L.) Webb ex Prantl (Brassicaceae), spiderflower, Cleome hassleriana Chod. (Capparaceae), and garden nasturtium, Tropaeolum majus L. (Tropaeolaceae). Females deposited most eggs on B. napus; T. majus was least preferred. The rate of survival from neonate to pupa was highest on B. napus followed by C. hassleriana, T. majus, and D. sophia. The rate of development of female larvae on Brassicaceae was similar to that on non-Brassicaceae; pupal development was slowest on non-hosts. Female pupae were heaviest on B. napus and lightest on D. sophia. Adult females were heaviest when reared on B. napus and lightest on T. majus and D. sophia. Females reared on D. sophia had the smallest forewings; forewing areas for females on other plants were similar. Females reared on B. napus and C. hassleriana lived longer without food than those reared on D. sophia or T. majus. Males reared on T. majus lived for the shortest time without food. This specialist herbivore can exploit a range of food plants, including suboptimal Brassicaceae and species from other families. This trait appears to facilitate survival and reproduction of P. xylostella when preferred food plants are limiting or absent.