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TECHNICAL REPORTS

Ecological Risk Assessment

Are Leaves that Fall from Imidacloprid-Treated Maple Trees to Control Asian Longhorned Beetles Toxic to Non-target Decomposer Organisms?

^a Canadian Forest Service, Natural Resources Canada, 1219 Queen St. East, Sault Ste. Marie, ON, Canada, P6A 2E5
^b Ontario Ministry of Natural Resources, Forest Resources Group, Suite 400, 70 Foster Dr., Sault Ste. Marie, ON, Canada, P6A 6V5

^* Corresponding author (Dave.Kreutzweiser{at}nrcan.gc.ca).

Received for publication May 30, 2007. The systemic insecticide imidacloprid may be applied to deciduous trees for control of the Asian longhorned beetle, an invasive wood-boring insect. Senescent leaves falling from systemically treated trees contain imidacloprid concentrations that could pose a risk to natural decomposer organisms. We examined the effects of foliar imidacloprid concentrations on decomposer organisms by adding leaves from imidacloprid-treated sugar maple trees to aquatic and terrestrial microcosms under controlled laboratory conditions. Imidacloprid in maple leaves at realistic field concentrations (3–11 mg kg^–1) did not affect survival of aquatic leaf-shredding insects or litter-dwelling earthworms. However, adverse sublethal effects at these concentrations were detected. Feeding rates by aquatic insects and earthworms were reduced, leaf decomposition (mass loss) was decreased, measurable weight losses occurred among earthworms, and aquatic and terrestrial microbial decomposition activity was significantly inhibited. Results of this study suggest that sugar maple trees systemically treated with imidacloprid to control Asian longhorned beetles may yield senescent leaves with residue levels sufficient to reduce natural decomposition processes in aquatic and terrestrial environments through adverse effects on non-target decomposer organisms.

Abbreviations: dbh, diameter at breast height • HPLC, high-performance liquid chromatography