Economic Injury Levels for Colorado Potato Beetle (Coleoptera: Chrysomelidae) on ‘Norland’ Potatoes in Manitoba

Abstract

In a plot of the early potato ‘Norland,’ densities of the Colorado potato beetle, Leptinotarsa decemlineata (Say), were manipulated on individually caged plants so that each plant was exposed throughout the growing season to a constant multiple of the density in an insecticide-free field plot. There was a linear relationship between yield and beetle density in 1983 and 1985; a curvilinear relationship was apparent in 1984. The differences in yields between commercial and insecticide-free plots were close to those predicted by the relationships derived from the caged plants. Based upon the average relationship of yield and beetle density for the three years, a decision-making model was developed. The economic injury level, expressed as Colorado potato beetle larvae per plant at the first bloom stage, was (Cost of control [$ per ha])/(Market price of tubers [$ per kg] × Expected yield in the absence of insects [kg per ha] × 0.022865). Typical values for the economic injury level under conditions in Manitoba ranged from 0.14-0.82 larvae per plant. A control decision system, which uses criteria of percentage defoliation of plants and an economic threshold to be compared with estimates of larval abundance, is proposed.