Bottom-up and top-down forces in plant-herbivorous insect-natural enemy tri-trophic interactions

ABSTRACT

In agro-ecosystems, variations in fertilization and irrigation to plants not only trigger bottom-up effects on herbivorous insect pests, but also influence the strength of top-down forces (via arthropod natural enemies) in controlling the herbivores. The two forces act in concert shaping the plant-arthropod communities. Using tomato Solanum lycopersicum as host plant, the tomato leaf miner Tuta absoluta, the whitefly Bemisia tabaci and the aphid Macrosiphum euphorbiae as herbivorous insects, Macrolophus pygmaeus as predator, we investigated how nutrient (nitrogen) and water inputs to tomato plants trigger bottom-up effects on the herbivores, the predator, as well as their interactions. The experiments are performed at both individual and population levels. We found that (i) nitrogen and water inputs can trigger strong bottom-up effects on both the herbivorous as well as the predator; (ii) the bottom-up effects are equally strong even though plants use different strategies to cope with nitrogen and water limitations; and (iii) nutrient inputs can influence the strength of indirection interactions between the two herbivores shared by one predator. These findings can not only enhance our understanding on how environmental factors influence plant-herbivore-natural enemy tri-trophic interactions, but also help optimize fertilization and irrigation regimes without losing the effective control of herbivorous pests.