The effect of benomyl and some related compounds on Lumbricus terrestris and other earthworms

Earthworm populations in apple orchard plots sprayed with benomyl and thiophanate‐methyl were greatly reduced. Lumbricus terrestris, a surface‐feeding species, was not found in the treated plots. Captive worms would not feed on leaf material with spray deposits of benomyl, MBC and thiophanate‐methyl at 1.75 μg/cm2, and feeding was significantly reduced when deposits were 0.87 μg/cm2. There was 100 % kill of worms in pots of soil within 14 days following a benomyl drench at the rate of 7.75 kg/ha, and a 60 % kill following a drench at the rate of 1.55 kg/ha. Worms immersed for 1 min in benomyl suspensions of 0.05 or 0.5 % died within 27 and 13 days respectively; those immersed in lower concentrations would not feed for 2 weeks but eventually did so. It is suggested that the lethal effects of benomyl may be due to anti‐cholinesterase activity of the carbamate moiety of the molecule.