Effect of Bacillus thuringiensis and a pyrethroid insecticide on the leaf microflora of Brassica oleracea

In a field experiment comparing the effect of treatment with Bacillus thuri ngiensis (Bt) and the pyrethroid insecticide, cypermethrin, on leaf microfl ora across the growing season, no significant differences mere found, apart from more bacteria on cypermethrin-treated leaves on 24 September (P < 0.0 5). No effect was seen on fungal diversity or numbers. In contrast, the pyr ethroid insecticide inhibited growth of 44% of bacterial isolates tested in vitro; Bt was not inhibitory. Bacillus thuringiensis numbers on treated le aves increased throughout the season, following repeated applications.