Consequences of removing a keystone herbivore for the abundance and diversity of arthropods associated with a cruciferous shrub

1. The effect of the removal of Timarcha lugens (Chrysomelidae), one of the main herbivores of Hormathophylla spinosa (Cruciferae), on the abundance of co-occurring phytophagous insects, the abundance of non-phytophagous arthropods (detritivores, predators, and parasitoids), and the structure and diversity of the entire arthropod community, was studied for 3 years (1999–2001). 2. There was competition between T. lugens and co-occurring herbivores; the removal of T. lugens was correlated with an increase in the abundance of sapsuckers, flower-feeders, and, above all, folivores. 3. Timarcha lugens also had an indirect effect on arthropods belonging to other trophic levels; the abundance of predators increased significantly after the removal of T. lugens. 4. Community composition was affected by the experimental removal. In addition, the diversity of the overall community increased after removal of T. lugens. 5. The study demonstrated experimentally that T. lugens has a significant effect not only on other species belonging to the same trophic level, but also on the abundance of species belonging to higher trophic levels, and, consequently, on the entire structure and diversity of the complex community in which it is immersed.