We tested the role of salicylic acid (SA) and jasmonic acid (JA) in altering the tomato plant's defense against herbivory by tobacco hornworm. Treatments of SA or JA were topically applied to tomato plants, hornworm consumption was allowed to proceed for 12 days, and harvest analyses were performed Measurements taken included a subjective plant rating (1-10 score), plant dry mass, caterpillar mass, and the number of times the caterpillars fell off the plant. Results showed significant effects of exogenously applied SA and JA on the defense of tomato plants against insect herbivory. Plants treated with SA had little resistance to the feeding caterpillars and the plant lost more biomass to them. JA, in contrast, apparently increased the defensive mechanisms of the plant, resulting in lower caterpillar growth and increased caterpillar detachment from plants. The data are consistent with a model where JA, endogenous or exogenously applied, is necessary for defense against insect herbivory and SA disrupts JA biosynthesis and/or pool accumulation.
Iverson, Aaron L.; Iverson, Louis R.; Eshita, Steve. 2001. The effects of surface-applied jasmonic and salicylic acids on caterpillar growth and damage to tomato plants. Ohio Journal of Science. 5: 90-94.