Cross-resistance to Bacillus sphaericus strains in Culex quinquefasciatus

Laboratory and field-collected strains of Culex quinquefasciatus that were selected with Bacillus sphaericus strain 2362 in the laboratory for about 100 generations and attained 37- and 31-fold resistance, respectively, did not show marked cross-resistance to Bacillus thuringiensis spp. israelensis; only 2-3-fold tolerance was noted. However, they showed significant levels of cross-resistance to strains 1593 (6-22-fold) and 2297 (4-12-fold) of B. sphaericus. Possible mechanisms and management implications are discussed.