Induced tomato defenses mediated by jasmonic acid do not have a major effect on the density of predator biological control agents

Abstract

Plants have developed different defense mechanisms to protect themselves from the attack of herbivores. Plant defenses can be categorized into two types: constitutive, which are present before herbivore attack, and induced, which are activated upon attack. Some herbivores have developed the ability to neutralize either or both types of plant defenses, and plant defenses may act against their own interest when they negatively affect herbivore’s natural enemies such predator insects and mites. Here we investigated whether herbivore-induced tomato defenses mediated by jasmonic acid (JA) affect the density of predator biological control agents and thus affect biological pest control negatively. Specifically, we assessed predator–herbivore abundances in greenhouse experiments on two tomato genotypes, a wild type (Castlemart) expressing the JA-mediated defense pathway and a mutant of the wild type (def-1) unable to activate this defense path. Plants were infested with either Bemisia tabaci, a pest that suppresses the activation of the JA defense path, or Frankliniella occidentalis, a pest species that induces JA defenses. As predators, we used four species of natural enemies, two phytoseiid mites and two predatory bugs, one of each pair able to colonize tomato crops (Typhlodromus (A.) recki, Macrolophus pygmaeus) and the other not (Amblyseius swirskii, Orius laevigatus). Results suggest that JA-mediated defenses do not have a negative impact on predator density. Instead, glandular trichomes likely contributed to the unsuccessful pest control. Yet, JA-mediated defenses are key for plant protection against herbivore species that cannot avoid this line of defense.