Contrasting Effects of Methyl Jasmonate and Methyl Salicylate on Coffee Plant Defenses against the Southern Red Spider Mite

Herbivory by mites often activates both jasmonate and salicylate signaling pathways in plants. While the role of jasmonic acid (JA) pathway in inducing plant defenses against mites is well established, the contribution of salicylic acid (SA) remains under debate. In previous studies, we found that herbivory by the mite Oligonychus ilicis (McGregor) (Acari: Tetranychidae) triggered the accumulation of both SA and JA, but increased plants susceptibility to subsequent herbivores. Here, we investigated the relative importance of SA and JA signaling pathways in coffee resistance to O. ilicis by applying methyl jasmonate (MeJA) and methyl salicylate (MeSA) as elicitors. To address this question, we combined behavioral assays (host selection and performance) with chemical analyses to attempt to identify and quantify secondary metabolites in plants treated with two concentrations of the elicitors (1.5 mM and 3.0 mM). Treatment with MeSA at 3.0 mM increased mite attraction but did not affect their performance. In contrast, treatment with MeJA at 3.0 mM reduced mite performance without altering mite preference, confirming the defensive role of the JA pathway. Levels of total phenolic compounds were not affected, but target analyses revealed that some phenolics were up-regulated by the elicitor treatments, such as syringic acid and coumaric acids in MeSA-treated plants and o-coumaric acid in MeJA-treated plants. By demonstrating the contrasting effects of MeJA and MeSA on the responses of coffee plants, our study extends the understanding of phytohormone-mediated defenses, providing guidance for sustainable pest management and deepening our comprehension of arthropod-plant interactions.