Monday, December 10, 2007 - 10:17 AM

Functional complementarity among predators and pathogens strengthens herbivore suppression

Ricardo Ramirez, and William Snyder, Washington State University, Dept. of Entomology, FSHN 166, Pullman, WA

A key ecosystem service provided by natural enemies is the control of herbivores, which may be impacted by changing patterns of enemy diversity. The beetle Leptinotarsa decemlineata, a pest of potatoes, has a complex life history with egg, larva and adult occurring on plant foliage, while the last instar larva burrows into the soil to pupate. A diverse community of enemies attacks different beetle stages both aboveground, where arthropod predators and parasitoids are key players, and belowground, where several pathogen species attack fossorial beetle stages. Thus, herbivore suppression might be the most complete when a functionally diverse enemy community of both predators and pathogens, partitioning attacks among the different beetle stages, is present. Conversely, adding additional species within either the predator or pathogen communities may lead to functional redundancy, and little improvement in herbivore suppression. In field cages, using a substitutive experimental design, we manipulated species richness (0, 1, 2, or 5 enemy species present) creating all possible enemy compositions of three predator species aboveground and three pathogen species belowground. We then recorded the impact of these manipulations on beetle survival. Overall, increasing enemy diversity increased herbivore suppression. More importantly, improvement on herbivore suppression only occurred when both predators and pathogens were present, suggesting that the predators and pathogens are working complementary.

Species 1: Coleoptera Chrysomelidae Leptinotarsa decemlineata (Colorado potato beetle)