We report the comparative inducing effects of a phytopathogen and a herbivorous arthropod on the performance of an herbivore. Tomato, Lycopersicon esculentum Mill., was used as the test plant, and tomato mosaic virus (ToMV) and corn earworm, Helicoverpa armigera Hübner, were used as the phytopathogen and herbivore, respectively. There were decreases in the efficiency of conversion of ingested food and efficiency of conversion of digested food when H. armigera was reared on tomato plants that had been previously inoculated with ToMV. However, virus inoculation did not affect feeding or oviposition preferences by H. armigera. In contrast, approximate digestibility, total consumption, relative growth rate, and relative consumption rate were lower for fourth-instar H. armigera that fed on plants previously damaged by the same herbivore. Feeding and oviposition were both deterred for H. armigera that fed on previously damaged plants. The duration of development of H. armigera was also prolonged under this treatment. Infection by ToMV and feeding damage by H. armigera increased the host plant's peroxidase and polyphenol oxidase activity, respectively, suggesting that the performance of H. armigera may be affected by the induced phytochemistry of the host plant. Overall, this study indicated that, in general, insect damage has a stronger effect than ToMV infection on plant chemistry and, subsequently, on the performance of H. armigera.