Effects of imidacloprid (Merit® 2F) on physiology of woody plants and performance of twospotted spider mite, fall webworm, and imported willow leaf beetle

We have shown that imidacloprid (Merit® 2F) can have growth enhancing effects on hybrid poplars that are independent of its insecticidal properties by increasing total leaf area. To test the generality of this pattern, a factorial experiment was conducted to evaluate the effects of imidacloprid on growth, biomass allocation, and gas exchange of the woody plants Populus nigra, Euonymus alatus, Betula nigra, and Salix sericea under high and low fertilization regimes. Laboratory bioassays were performed to test the effects of imidacloprid on the performance of twospotted spider mite (Tetranychus urticae), imported willow leaf beetle (Plagiodera versicolora), and fall webworm (Hyphantria cunea). After 44 days of exposure, imidacloprid significantly increased total plant biomass and total leaf area of P. nigra, but had no effect on the three plant species, suggesting that the growth-enhancing effects of imidacloprid are species specific. Imidacloprid increased the fecundity of twospotted spider mite on E. alatus in the low fertility treatment, raising egg production to levels observed in the high fertility treatment. As expected, imidacloprid decreased survival of imported willow leaf beetle on S. sericea. Surprisingly, imidacloprid also decreased larval growth and survival of fall webworm on B. nigra, S. sericea, and P. nigra.Bayer CropScienceOhio Agricultural Research and Development Center, The Ohio State Universit