Methyl Jasmonate and Methyl Salicylate Differentially Modulate Direct and Indirect Defenses in Coffee Plants Against the White Mealybug

ABSTRACT

Salicylic acid (SA) and jasmonic acid (JA) are key phytohormones regulating induced plant defenses against insect herbivores. Phloem‐feeding insects often activate the SA pathway, although exceptions in which both SA and JA are induced, such as during herbivory by the white mealybug Planococcus citri (Risso) (Hemiptera: Pseudococcidae) on coffee plants, highlight the need to clarify the relative roles of these pathways in modulating plant resistance. This study investigated how activation of the SA and JA pathways in coffee plants, Coffea arabica L. (Rubiaceae), affects direct plant defenses against P. citri and indirect defenses through the emission of volatiles attractive to the predatory lady beetle Cryptolaemus montrouzieri Mulsant (Coleoptera: Coccinellidae). Coffee plants were treated with exogenous doses of the phytohormone derivatives methyl salicylate (MeSA) and methyl jasmonate (MeJA). Direct defenses were assessed through P. citri preference and performance assays, whereas indirect defenses were evaluated using olfactory preference assays with C. montrouzieri . Application of MeSA to coffee plants, regardless of dose, increased host preference by P. citri nymphs compared with untreated plants, whereas treatment with MeJA, either alone or in combination with MeSA, particularly at higher doses, reduced herbivore preference. Treatment with any of the elicitors, irrespective of dose, delayed P. citri development, particularly on plants treated with MeJA alone. MeJA also induced indirect defenses, with or without P. citri infestation, triggering the emission of volatiles attractive to C. montrouzieri , whereas MeSA treatment reduced the attractiveness of plant volatiles to the predator. The combination of MeSA and MeJA in mealybug‐infested plants also reduced plant attractiveness to the lady beetle. Overall, activation of the jasmonate pathway played an important role in both direct and indirect defenses against the mealybug, whereas activation of the salicylate pathway produced inconsistent effects on direct defenses and did not regulate indirect defenses.