Intraguild interactions among key predators in Mediterranean pear orchards

Intraguild interactions have a strong effect on the population dynamics and structure of the community of arthropods in ecosystems. Ants are key species in Mediterranean pear orchards due to the mutualistic relationship they establish with honeydew-producing hemipterans and its impact on other natural enemies, such as spiders and predatory mirids. The aim of this work was to assess intraguild interactions among the main predators in pear orchards, since such interactions may affect pest suppression. The interactions among the ant Lasius grandis, the myrmecomorphic mirid Pilophorus gallicus and two species of spiders (Oxyopes lineatus and Philodromus lividus) was assessed in the presence/absence of each species in a complete factorial design. The arena consisted of a 2-liter clear plastic jar with a pear seedling. Ant nests were connected to the arena by means of a plastic tube. The survival of P. gallicus was significantly reduced by ants and spiders. In addition, the survival of both spiders was significantly affected by L. grandis, with O. lineatus being more adversely affected than P. lividus. In arenas with ants, the addition of the spider O. lineatus further decreased P. gallicus survival, whereas when P. lividus was incorporated to the arena the survival of the mirid increased significantly. These findings corroborate that L. grandis is the top predator in Mediterranean pear orchards and that the role of other predators in pest regulation in this agroecosystem is expected to be conditioned by their interactions with ants.