Does aerial spraying of Bacillus thuringiensis subsp. kurstaki (Btk) pose a risk to nontarget soil microarthropods?

Abstract

This field study was carried out to investigate whether application of an aerial spray containing Bacillus thuringiensis subsp. kurstaki (Btk) to control the western spruce budworm (Choristoneura occidentalis Freeman, 1967) had any measurable effects on aspects of the abundance, distribution, diversity, and feeding behaviour of nontarget soil microarthropods. Although total abundance and species richness (N0) of Collembola declined significantly in samples taken 3 weeks after spraying, this decline occurred in the control plots as well as in plots sprayed with Btk. Values for the diversity indices N1 and N2 were not affected by the treatment. Correspondence analysis did not identify changes in collembolan communities following the aerial application of Btk. Total abundance of mites and populations of different suborders (Prostigmata, Mesostigmata, and Oribatida) were not significantly affected by application of Btk, or by the time of year that the samples were collected. There was no evidence of a selective reduction in the surface-dwelling portions of the collembolan and mite communities following exposure to Btk. Similarly, the experimental spray did not cause a decline in the abundance of the guild of Collembola known to feed on bacteria, and the proportion of bacteria in the diet of these Collembola following application of Btk was also unchanged.