Tomato (Solanum lycopersicum) volatiles prime defenses against Manduca sexta in the field

Recent efforts in biological control have explored using the attractive qualities of herbivore-induced plant volatiles (HIPVs) to draw natural enemies to protect crops throughout the field.  Methyl salicylate (MeSA) is a common HIPV used commercially to attract natural enemies, but is closely related to the signaling hormone salicylic acid (SA).  SA is known to interfere with the jasmonic acid (JA) -signaling pathway, which is responsible for regulating defenses against chewing herbivores.  We investigated the possible interaction of MeSA lures (PredaLure®) and herbivory to determine if MeSA positively or negatively affects tomato defense against herbivores.  We exposed tomatoes in the field to PredaLure® for two days and then induced leaves with wounding and Manduca sexta regurgitant every 24 hours for three days.  Subsequently, we measured herbivore-associated defenses, specifically proteinase inhibitors, polyphenol oxidase, and peroxidase protein activity within damaged leaves, and weight gain of Spodoptera exigua, a generalist lepidopteran.  We also measured pathogen-associated defenses (SA-pathway): phenylalanine ammonia-lyase activity and growth of naturally occurring biotrophic fungal pathogens (Cladosporium and Alternaria).  We found that MeSA decreased tomato resistance to chewing herbivory up to four meters downwind of the lure, but it increased resistance to pathogens, indicating cross-talk between the JA and SA pathways.  We suggest that while MeSA lures may attract a broad suite of natural enemies, they decrease tomato resistance to chewing herbivores in the immediate area around the lure by interfering with the JA pathway.