Comparative efficacy of Beauveria bassiana, Bacillus thuringiensis, and aldicarb for control of Colorado potato beetle in an irrigated desert agroecosystem and their effects on biodiversity

Five weekly applications of Beauveria bassiana (Balsamo) Vuillemin, a genetically engineered isolate of Bacillus thuringiensis Berliner (Raven), and aldicarb (Temik) were compared for control of Colorado potato beetle, Leptinotarsa decemlineata (Say) in an irrigated desert cropping system. B. thuringiensis was applied using low and high label rates (1.17 and 7.0 l ha−1). B. bassiana was applied at 5 × 1013 spores ha−1. Aldicarb (RhônePoulenc), applied at 3.37 kg a.i. ha−1 provided the greatest beetle control and potato yields (45 metric tons ha−1), but overall lowest biodiversity in nontarget organisms, particularly predatory Heteroptera. Low and high rates of B. thuringiensis produced fair to excellent beetle control, yielded 33 and 40 metric tons ha−1 and enabled good survival in predatory Heteroptera and other nontargets. Plots treated with B. bassiana resulted in poor control of beetles prior to row closure after which fair to good control was achieved. Yield in the Beauveria-treated plots was 33 metric tons ha−1 and effect on biodiversity was comparable to the Bt-treated plots. The lowest number of overwintering adult L. decemlineata was found in the plots treated with bacteria and fungi (0.68–0.84 adults/0.03 m−3 of soil) and the highest was found in control and aldicarb plots (3.44 and 1.84 adults/0.03 m3 of soil). Aphids and leafhoppers showed higher densities in plots treated with microbial control agents, but were eliminated from plots treated with aldicarb.