Pests, but not predators, increase in mixed fruit tree–vegetable plots compared to control vegetable plots in a Mediterranean climate

Abstract

Mixed fruit tree–vegetable systems simultaneously combine the production of vegetables at the ground level with that of fruits in tree canopies. We tested whether such crop diversification may reduce herbivores on the vegetable crop in the case of an apple fruit–cabbage association. For this purpose, we monitored arthropod pests and natural enemies during six sampling sessions over one growing season with direct observations and pitfall traps. Unexpectedly, we found that four out of seven pest stages [the aphid Myzus persicae Sulzer (Aphididae), lepidoptera eggs and caterpillars, and pupae of whiteflies] were more abundant or more frequent in the mixed fruit tree–vegetable plots than in control plots. In contrast, we observed more of three out of the six main predator taxa (chilopods, earwigs and ants) in the control plots. The mechanisms possibly explaining our results include better microclimatic conditions, the dilution of predators and increased bird abundance in the agroforestry plots as well as the longer generation time of predators versus pests.