Effects on litter-dwelling earthworms and microbial decomposition of soil-applied imidacloprid for control of wood-boring insects.
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 LC(50) of 5.7 mg kg(-1), an LC(10) of about 2 mg kg(-1) and significant weight losses among survivors at 3 mg kg(-1). Weight losses resulted from a physiological effect rather than from feeding inhibition. There were no effects on cocoon production among survivors at 3 mg kg(-1). The LC(50) for E. fetida was 25 mg kg(-1), with significant weight losses at 14 mg kg(-1). There were no significant effects on microbial decomposition of leaf material at the maximum test concentration of 1400 mg kg(-1).


CONCLUSIONS
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 litter reach or exceed about 3 mg kg(-1).
Kreutzweiser
David P
DP
Canadian Forest Service, Natural Resources Canada, Ontario P6A 2E5, Canada. Dave.Kreutzweiser@nrcan.gc.ca
Good
Kevin P
KP
Chartrand
Derek T
DT
Scarr
Taylor A
TA
Holmes
Stephen B
SB
Thompson
Dean G
DG
D000818:Animals; D004305:Dose-Response Relationship, Drug; D007093:Imidazoles / Q000494:pharmacology*; D007313:Insecta / Q000187:drug effects*; D007306:Insecticides / Q000494:pharmacology*; D000073943:Neonicotinoids; D009574:Nitro Compounds / Q000494:pharmacology*; D009835:Oligochaeta / Q000187:drug effects*; D012988:Soil Microbiology; D013997:Time Factors; D014934:Wood / Q000469:parasitology*
D007093:Imidazoles; D007306:Insecticides; D000073943:Neonicotinoids; D009574:Nitro Compounds; C082359:imidacloprid