An Alternative Approach for Evaluating the Efficacy of Potential Biocontrol Agents of Weeds. 1. Inverse Linear Model

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Abstract
Methods for evaluating the efficacy of potential classical biocontrol agents were outlined for a model biocontrol agent-weed-crop system. A proposed biocontrol agent (the fiddleneck flower gall nematode), its weed host (coast fiddleneck), and wheat were used as representative organisms. An additive experimental design (inverse linear model) was used. Regression of the reciprocal of the average plant biomass of each species onto the density of itself and the other plant species yielded competitive indices that measure the competitive ability of the plants. The results of 2 yr of field experiments revealed a dramatic change in the competitive interaction between fiddleneck and wheat due to the nematode. During the 1986–87 season in the absence of the nematode, fiddleneck intraspecific competition was 33 times stronger than interspecific competition with wheat. In the presence of the nematode, intra- and interspecific competition of fiddleneck were nearly equal. Only the coefficients that measure interspecific competition changed significantly in the presence of the nematode while the coefficients for intraspecific competition did not.