Monitoring native non-target Lepidoptera for three years following a high dose and volume application ofBacillus thuringiensissubsp.kurstaki

The operational use of Bacillus thuringiensis subsp. kurstaki (Btk) to control the western spruce budworm in the mountainous terrain of British Columbia, Canada, gives variable results at the registered dose of 30 BIU ha − 1 in 2.4 L ha − 1. Btk (Foray 48B®, 60 BIU ha − 1 in 4.8 L ha − 1) was applied experimentally in 1996 over 150-ha of western spruce budworm-infested Douglas-fir forest to determine if increasing both the dose and volume of Btk applications gives more uniform and effective control. We sampled native caterpillars on the shrub Ribes cereum Douglas in this and a similar, untreated area 2 km away from 1996 to 1998 to assess the impact of this high dose and volume Btk application on non-target Lepidoptera. The numerically dominant lepidopteran species were Euhyponomeutoides gracilariella Busck (52%) and Gelechia ribesella Chambers (32%). The remaining 16% of the guild was comprised of numerous sparsely distributed species. Total larval abundance was significantly lower on plants that were sprayed with Btk than on plants that were covered to exclude Btk within the treatment area in the year of application. Geometrids appeared to be less affected by the treatment than other taxa. Both G. ribesella and E. gracilariella appeared to make a full recovery by the second year post-treatment, but we did not find a full recovery of the sparsely distributed species.