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 black poplar 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 Populus nigra, Euonymus alatus, Betula nigra, and Salix sericea grown under high and low fertilization regimes. Additionally, 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. The other three woody species also had greater growth when treated with imidacloprid, but the effect was not significant. Imidacloprid increased the fecundity of twospotted spider mite on E. alatus in the low fertility treatment, raising egg production to the same level observed in the high fertility treatment. Imidacloprid decreased larval growth and survival of fall webworm on B. nigra, and P. nigra, and imported willow leaf beetle on S. sericea.