Soil amendment effects on survivorship and development time of Colorado potato beetles

Plants grown on organically managed soils have been found to be less favorable hosts for a number of insect pests when compared with plants grown using synthetic fertilizers. The present study tested if applications of compost containing lignocellulosic substrates and several biocontrol treatments known to suppress soil-borne diseases (a hypovirulent strain of the fungus Rhizoctonia solani, a bacterium Bacillus subtilis, and a parasitic fungus Trichoderma virens) had a similar effect. Experiments were conducted on caged potato plants in the greenhouse. Compost had no effect when used together with a synthetic fertilizer, but increased larval survivorship and rate of development when used alone. Feeding on plants treated with B. subtilis alone or in combination with R. solani delayed development of the Colorado potato beetle larvae when compared with larvae feeding on plants grown in any of the other biocontrol treatments and the control plants with no biocontrol agents added. Larval survivorship was similar among the treatments. In a follow-up experiment, it was found that when used alone at a higher dose, R. solani reduced both survivorship and rate of development of Colorado potato beetle larvae.