Effects on litter-dwelling earthworms and microbial decomposition of soil-applied imidacloprid for control of wood-boring insects

摘要

BACKGROUND:Imidacloprid is an effective,systemic insecticide for the control of wood-boring insect pests in trees.Systemic applications to trees are often made by soil injections or drenches,and the resulting imidacloprid concentrations in soil or litter may pose a risk of harm to natural decomposer organisms.The authors tested effects of imidacloprid on survival and weight gain or loss of the earthworms Eisenia fetida (Savigny) and Dendrobaena octaedra (Savigny),on leaf consumption rates and cocoon production by D.octaedra and on microbial decomposition activity in laboratory microcosms containing natural forest litter.RESULTS:Dendrobaena octaedra was the most sensitive of the two earthworm species,with an LC50 of 5.7 mg kg~(-1),an LC10 of about 2 mgkg~(-1) and significant weight losses among survivors at 3 mgkg~(-1).Weight losses resulted from a physiological effect rather than from feeding inhibition.There were no effects on cocoon production among survivors at 3 mgkg~(-1).The LC50 for E.fetida was 25mgkg~(-1),with significant weight losses at 14mgkg~(-1).There were no significant effects on microbial decomposition of leaf material at the maximum test concentration of 1400 mgkg~(-1).CONCLUSION:The results indicate that,when imidacloprid is applied as a systemic insecticide to the soil around trees,it is likely to cause adverse effects on litter-dwelling earthworms if concentrations in the Utter reach or exceed about 3mg kg~(-1).