An Alternative Approach for Evaluating the Efficacy of Potential Biocontrol Agents of Weeds. 2. Path Analysis

Path analysis was used to assess the efficacy of the fiddleneck flower gall nematode as a weed biocontrol agent of coast fiddleneck in competition with wheat during two years of field experiments. The path analysis revealed that the number of inflorescences/plant for fiddleneck and the number of heads/plant for wheat were the most important yield components that determine fecundity and seed yield. The density of fiddleneck had a much greater impact on the yield components of fiddleneck than did the density of wheat or the nematode rate of inoculation. The nematode had its greatest negative impact on the number of seeds/flower of fiddleneck and its greatest positive impact on the number of heads/plant of wheat. Path analysis predicts that a biocontrol agent that has a large negative direct effect on the number of inflorescences/plant for fiddleneck would be more efficacious in decreasing fecundity and seed yield than an agent that only impacts the number of flowers/inflorescence, seeds/flower, or biomass/seed. Nomenclature: Coast fiddleneck, Amsinckia intermedia Fischer and Meyer #3 AMSIN; wheat, Triticum aestivum L. \u27Anza\u27; fiddleneck flower gall nematode, Anguina amsinckiae (Steiner and Scott, 1935) Thorne, 1961

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

Methods for evaluating the efflicacy 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. Nomenclature: Coast fiddleneck, Amsinckia intermedia Fischer and Meyer #3 AMSIN; wheat, Triticum aestivum L. \u27Anza\u27; fiddleneck flower gall nematode, Anguina amsinckiae (Steiner and Scott, 1935) Thorne, 1961

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

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 two years of field experiments revealed a dramatic change in the competitive interaction between fiddleneck and wheat due to the nematode. During the 1986-1987 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. Nomenclature: Coast fiddleneck, Amsinckia intermedia Fischer and Meyer #3 AMSIN; wheat, L. \u27Anza\u27; fiddleneck flower gall nematode, Anguina amsinckiae (Steiner and Scott, 1935) Thorne, 1961