Submitted to: Biological Control
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/11/1997
Publication Date: N/A
Citation: Interpretive Summary: Potato production is a $2 billion industry in the U.S. The Colorado potato beetle (CPB) is the most devastating defoliator of potato in the American Northeast and Central potato producing states. It is increasing in importance in other potato growing regions. CPB is noted for its ability to quickly develop resistance to chemical insecticides. Uncontrolled or poorly ymanaged populations of CPB can cause a total reduction of tuber yields. A insect-killing fungus was applied to potato plots, with and without a CPB predator in an attempt to reduce field populations of CPB. Their efficacy was compared to currently utilized methods of chemical insecticide control. The observed mortality in the fungus-treated larval populations was over 90% 2 days after the last 4 applications. The respective cross season efficacies of the treatments in reducing populations of large larvae were 76.6, 50.2 and 78% with the fungus, insecticide, and fungus-predator treatments. Large larvae cause most of the defoliation of potato plants. The use of the fungus applied rapidly to young larvae eliminated most of this pressure. Foliar applications of the fungus provided substantial foliar protection and proved to be slightly but significantly more effective than no treatment. Studies as ours could be a valuable tool to use as an alternative to chemical insecticides and CPB resistance development to them. For example, a grower could knock down his CPB population with a chemical insecticide one year, and the following year he would start out with a low overwintering beetle population which he could control with an alternate strategy like the fungus, and stay away from chemical insecticides for a time.
Technical Abstract: Conidia of the fungus Beauveria bassiana were applied to potato plots, with and without the predator Perillus bioculatus, in an attempt to reduce field populations of Colorado potato beetle (CPB), and to compare their efficacy to currently utilized methods of chemical insecticide control. Unformulated conidia were applied as a water suspension at the rate of 5* 10**13 conidia aha**-1. Small nymphs of the predator were released at the rate of one nymph per plant. The strategy combined four rapid (at 3 to 4 d intervals) early-season foliar applications of the fungus and four releases (at weekly intervals) of the predator. The observed rate of mycosis in the treated larval populations was over 90% 2 d after the last fungal application. The cross season densities of large larvae were 41.4, 9.7, 20.7 and 9.1 per plant in the control, Beauveria, insecticide, and Beauveria-Perillus treatments, respectively. The respective cross season percent efficacies of the treatments in reducing populations of large larvae were 76.6, 50.2 and 78.0 percent with the Beauveria, insecticide, and Beauveria-Perillus treatments. Large larvae cause most of the defoliation of potato plants. The use of B. bassiana applied rapidly to early instars eliminated most of this pressure. The role of the predator in limiting defoliation through predation on eff masses and small larvae was unclear. Yields of marketable tubers showed no significant differences that would be expected due to treatments as suggested by differences in defoliation ratings and population counts. 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 CPB for crop protection.