Effects of jasmonate-induced defenses in tomato on the potato aphid, Macrosiphum euphorbiae

Jasmonates such as jasmonic acid (JA) are plant-signaling compounds that trigger induced resistance (IR) to a broad range of arthropod herbivores. JA-dependent defenses are known to reduce the growth and survivorship of many chewing insects, but their impact on piercing-sucking insects such as aphids has not been extensively investigated. In this study, induced resistance was activated in tomato (Lycopersicon esculentum Mill) (Solanaceae) using a foliar application of synthetic JA, and control plants were treated with carrier solution. The life parameters of individual potato aphids and their progeny (Macrosiphum euphorbiae Thomas) (Hemiptera: Aphididae) were evaluated on the unsprayed leaves of plants in order to access the systemic effects of the foliar treatments. IR significantly reduced the longevity and net reproduction of adult aphids, as well as the percentage of juveniles to survive to maturity. These results indicate that JA application induces systemic defenses in tomato that have a direct negative impact on aphid survivorship. This study also examined aphid honeydew excretion, in order to evaluate the potential influence of induced resistance on aphid feeding behavior. The average honeydew production per aphid was comparable on plants with or without JA treatment, indicating that JA-dependent defenses did not deter feeding. This suggests that the observed effects of JA on aphid survivorship were due to antibiotic rather than antixenotic factors. In addition to studying the effects of JA treatment on a tomato cultivar that is susceptible to aphids, this study also examined the effects of exogenous application of JA on tomato plants that carry the aphid resistance gene, Mi-1.2. JA application did not significantly enhance or inhibit aphid control on resistant tomato. These findings expand our understanding of the effects of JA-dependent defenses on piercing-sucking insects, and of the potential interactions between induced resistance and R-gene mediated aphid resistance in tomato.