Effects of intraspecific plant defense diversity on aphid population growth and predation

Plant defenses regulate herbivore populations and mediate predator-prey interactions. Yet most studies on the effects of defenses on arthropods focus on individual plants; therefore, not much is known on whether the defense phenotype of neighboring plants affects herbivores and predators. In this study w e tested the effects of plant defense diversity and predators (Hippodamia convergens) on the potato aphid Macrosiphum euphorbiae population growth. To manipulate tomato (Solanum lycopersicum) defenses we independently primed two defensive pathways the jasmonic acid (JA) and salicylic acid (SA) pathways. To test the effects of plant defense diversity, we set up four treatments: SA monoculture, JA monoculture, untreated control monoculture, and a mixture of SA, JA, and controls. To test the effects of predators on aphid suppression, half of the treatments received predators. Each cage contained 3 plants inoculated with 100 aphids per plant and in cages that contained predators, one ladybug was added to every 100 aphids. Afterwards, predators and aphids were allowed to feed for 5 days and the number of aphids was recorded.

Our results indicate that predators strongly suppressed aphid populations. Additionally, defense diversity influenced aphid population growth. Mixtures and SA-monocultures exhibited lower aphid population growth compared to JA and control monocultures, suggesting that priming salicylate defenses have stronger effects on suppressing aphids.

Understanding how intraspecific diversity in plant defense affects biocontrol and pest suppression could contribute to developing more efficient and sustainable control methods.