Effect of two commercial formulations of Bacillusthuringiensis suhsp. kurstaki on the forest earthworm Dendrobaenaoctaedra

The effects of Dipel®8L and Dipel®8AF (two formulations of Bacillusthuringiensis subsp. kurstaki (B.t.k.)) on the survival, growth, and reproduction of the forest earthworm Dendrobaenaoctaedra (Sav.) were studied in the laboratory using simple soil–litter microcosms. Dendrobaenaoctaedra was not adversely affected by an unformulated preparation of B.t.k. or by the aqueous formulation (Dipel®8AF) even at doses representing 1000× the expected environmental concentration (EEC). However, survival, growth, and cocoon production were significantly reduced in the presence of Dipel®8L at 1000× EEC, which is the level recommended for Tier I testing for environmental effects according to the Canadian guidelines for registration of naturally occurring microbial pest control agents. Further tests indicated that the toxic component of the Dipel®8L was the oil-based formulation blank. No significant deleterious effects on survival, growth, or reproduction were observed in microcosms sprayed with Dipel®8L at the EEC, 10× EEC, or 100× EEC. There was no evidence of a synergistic reaction between oil-based formulation ingredients and B.t.k., which would act to increase the susceptibility of D. octaedra to the bacterium.