Second-instar larvae of the phytophagous thrips, Thrips tabaci, consumed significantly more spider mite (Tetranychus urticae Koch) eggs than did any other T.tabaci life stage. We supplemented two plant diets with mite eggs to assess whether the inclusion of prey could make up completely for dietary deficiencies in the host plant. Therefore, turnip weed (Rapistrumrugosum L.) floral tissue (a major breeding host of T.tabaci) and cotton vegetative tissue (a host on which T.tabaci populations dwindle) were compared. In both cases, prey in the diet reduced the developmental time from egg to adult and increased fecundity over that achieved on a host-plant diet alone, but had no effect on immature mortality or adult life span. Females on turnip weed plus mite eggs produced more eggs than those on cotton cotyledons plus mite eggs. We discuss the role of facultative predation (or opportunism) in the ecology of T. tabaci.