Plants have evolved the ability to accumulate defensive chemicals in their tissues in response to insect herbivory. Although wounding of the plant occurs during herbivory, we found evidence that mechanical wounding, herbivory by Spodoptera exigua or Pieris rapae, and oral secretions from these herbivores are not equivalent in stimulating the cellular signaling pathways and chemical defenses in Arabidopsis. Oral secretions derived from salivary gland contents and regurgitate were tested separately since their relative role and importance in modifying plant responses is unknown. Transcription of marker genes was used to infer cell signaling through the jasmonic acid (JA) or salicylic acid (SA) pathways. Accumulation of glucosinolates was used to correlate the defensive response with the signaling pathway and plant treatment. It appears that oral secretions contain compounds that alter plant perception of the wounding caused by these chewing insects.