Laboratory Investigation of Five Inert Dusts of Local Origin as Insecticides against the Colorado Potato Beetle (Leptinotarsa decemlineata [Say])

The Colorado potato beetle (CPB) is an economically important pest on potatoes, which can cause significant damage if not controlled. Our laboratory trial was conducted to study the efficacy of five types of inert dusts (diatomaceous earth, quartz sand, Norway spruce wood ash, zeolite, and tree of heaven leaf dust) against the CPB. Efficacy was tested using three modes of application (MoA): MoA 1, in which the used inert dusts were applied to both leaves and insects: MoA 2, where just the leaves were pre-dusted: and MoA 3, where only the pests were pre-dusted. All three modes were tested on larvae (L1/L2 and L3/L4) and adults of CPB. Among the inert dusts applied to the adults, the highest efficacy was recorded for the diatomaceous earth treatment (13.3 &plusmn: 3.3%) in the first MoA and the wood ash treatment (6.7 &plusmn: 3.3%) in the second MoA after 7 days of exposure. Defoliation results for adults were most promising in the A. altissima leaf dust treatment in the first and second MoA (45.3 &plusmn: 8.2%) after 7 days of exposure. For the old larvae, wood ash was the most promising in regards to efficacy (26.7 &plusmn: 7.3%) and defoliation (app. 70.0%) after 7 days of exposure in the third MoA. For the young larvae, the most promising results at the end of the 7-day exposure period for efficacy were obtained from the treatment of diatomaceous earth (65.7 &plusmn: 22.9%). Defoliation rates for young larvae were also high, but most promising in the treatment of A. altissima leaf dust (41.0 &plusmn: 4.2%) in the second MoA. The results showed that the inert dusts were not very effective in controlling the CPB, with the exception of wood ash and diatomaceous earth, which showed some limited control. A. altissima leaf dust generated a low defoliation rate, possibly due to an antifeedant effect on the beetles.