Technical Abstract: Jasmonic acid (JA) and its derivatives mediate induced resistance against caterpillars and other herbivores that cause tissue disruption. Far less is known about the role of jasmonates in plant interactions with phloem-feeding insects such as aphids. This study compared responses in tomato (Solanum lycopersicum) to the potato aphid (Macrosiphum euphorbiae) and a chewing insect, the beet armyworm (Spodoptera exigua). Armyworms but not aphids upregulated genes involved in JA synthesis (lipoxygenaseD, allene oxide synthase2, and allene oxide cyclase) and response (proteinase inhibitorII and 1-deoxy-D-xylulose 5-phosphate synthase2). In contrast, aphids induced salicylic acid (SA) accumulation and upregulated the SA-responsive pathogenesis-related gene P4. This study also assessed aphid performance on mutant tomato lines that are deficient in JA synthesis (spr2, acx1) or perception (jai1-1), and that are highly susceptible to chewing insects. Aphid numbers were comparable on acx1, jai1-1, and wild-type plants, but aphid survival and reproduction were significantly lower on spr2. Transcripts encoding P4, '-dioxygenases, and divinyl ether synthase were also more abundant in spr2 than in wild-type plants, suggesting that spr2 may alter SA signaling and oxylipin metabolism in response to aphids. The spr2 mutation abolishes function of LeFAD7, a fatty acid desaturase involved in jasmonate synthesis. This study shows that alterations in fatty acid desaturation can enhance aphid resistance. Furthermore, our data suggests that jasmonates do not play a major role in limiting aphid population growth on tomato, and highlights potential trade-offs in plant defenses against different insect feeding guilds.