Early-season applications of the fungus Beauveria bassiana and introduction of the hemipteran predator perillus bioculatus for control of Colorado potato beetle

Unformulated conidia of the fungus Beauveria bassiana were applied to potato plots, with and without the hemipteran predator Perillus bioculatus, in an attempt to reduce field populations of Colorado potato beetle, Leptinotarsa decemlineata, and to compare their efficacy to currently utilized methods of chemical insecticide control. Dry conidia were mixed in a water/0.01% Silwet suspension and applied with a backpack sprayer, at a rate of 5 X 10(13) viable conidia/ha. Small nymphs (first and second instars) of the predator were released at the rate of one nymph/plant. Four rapid (at 3- to 4-day intervals) early-season (at the green row and touch in row growth stages of potato) foliar applications of the fungus and four releases (at weekly intervals) of the predator were made. The observed rate of mycosis in the treated larval populations was > 90% 2 days after the last fungal application. The seasonal treatment effects on small (first and second instars) and large (third and fourth instars) larvae were examined. There were no differences in densities of small larvae in any of the treatments. However, the seasonal densities of large larvae were 41.4, 9.7, 20.7, and 9.1/plant in the control, Beauveria, chemical insecticides (esfenvalerate plus piperonylbutoxide and oxamyl plus carbofuran), and Beauveria-Perillus treatments, respectively. The respective seasonal percent efficacies (control corrected) of the treatments in reducing populations of large larvae were 76.6, 50.2, and 78.0% with the Beauveria, insecticide, and Beauveria-Perillus treatments. Large larvae cause most of the defoliation of potato plants; B. bassiana applied at 3- to 4-day intervals to early instars eliminated most of this pressure. Applications of the fungus provided substantial foliar protection and proved to be significantly more effective than parallel insecticide treatments and much more effective than no treatment. The role of the predator in limiting defoliation through predation on egg masses and small larvae was unclear. Although yields of marketable tubers showed no treatment differences, the significant reductions in larval densities, the prevalence of infection in field collections, and the substantial foliage protection confirmed the potential of B. bassiana conidia to infect and kill Colorado potato beetle for crop protection.