It is a widely accepted view in weed biological control that additional stress factors, particularly interspecific plant competition are necessary to tip the balance in favour of the biocontrol agents. The effects of herbivory and competition on the target weed depend on the densities of these factors applied. However, only few impact studies exist that used different densities of one of these factors, and hardly any in which the density of both factors was varied. We established an impact experiment with houndstongue (Cynoglossum officinale L., Boraginaceae), an introduced rangeland weed in North America. Five different levels of below-ground herbivory by the biological control agent Longitarsus quadriguttatus and four different levels of grass competition were applied to potted houndstongue plants in summer 2000. Half of the replicates were harvested in early spring 2001 to measure the effect of the two factors on overwintering rosettes, and the remaining replicates in summer 2001 to analyze the impact on final biomass and reproductive output. The data are still being analyzed, but preliminary results indicate that interspecific competition had the largest effect on C. officinale.
Species 1: Boraginaceae Cynoglossum officinale (houndstongue)
Species 2: Coleoptera Chrysomelidae Longitarsus quadriguttatus
Keywords: Impact experiments, Biological weed control
The ESA 2001 Annual Meeting - 2001: An Entomological Odyssey of ESA