Plant defense mixtures result in distinct volatile blends with trade-offs for aphid resistance and biological control

Plants deploy multiple defense pathways to deter herbivores, with consequences that can drive predator–prey interactions. While the effects of interspecific variation in plant defenses on herbivores and natural enemy are well understood, far less is know about the consequences of intraspecific differences in defense phenotypes. This limits our ability to predict how plant trait diversity influences pest control. Herein, we tested how intraspecific defense diversity in tomato (Solanum lycopersicum Linnaeus) affects potato aphid populations (Macrosiphum euphorbiae Thomas) and interactions with the convergent ladybeetle (Hippodamia convergens Guérin-Méneville). We independently primed the jasmonic acid (JA) pathway and the salicylic acid (SA) pathway and established four treatments: monocultures of untreated controls, JA-treated plants, SA-treated plants, and mixtures of all three defense phenotypes. Half of the cages received one ladybeetle per 100 aphids. We hypothesized that defense mixtures would reduce aphid populations, increase their dispersal relative to monocultures, and strengthen predator effects. Instead, our findings suggest that while combining multiple defense phenotypes can directly limit herbivores, it may also disrupt predator-prey interactions. In the presence of predators, SA-treated monocultures resulted in the highest reduction in aphid density and population growth, while JA-treated monocultures led to increased aphid dispersal. Predator effects were reduced in defense mixtures which emitted a distinct volatile blend that partially overlapped with SA- and JA-treated monocultures but differed from controls. Integrating knowledge of defense pathways with natural enemy effectiveness is crucial for developing integrated pest management strategies that suppress pests both directly and through biological control.