VARIABLE CROSS-RESISTANCE TO CRY11B FROM BACILLUS-THURINGIENSIS SUBSPJEGATHESAN IN CULEX-QUINQUEFASCIATUS (DIPTERA, CULICIDAE) RESISTANT TO SINGLE OR MULTIPLE TOXINS OF BACILLUS-THURINGIENSIS SUBSP ISRAELENSIS

A novel mosquitocidal bacterium, Bacillus thuringiensis subsp. jegathe san, and one of its toxins, Cry11B, in a recombinant B. thuringiensis strain were evaluated for cross-resistance with strains of the mosquit o Culex quinquefasciatus that are resistant to single and multiple tox ins of Bacillus thuringiensis subsp. israelensis. The levels of cross- resistance (resistance ratios [RR]) at concentrations which caused 95% mortality (LC95) between B. thuringiensis subsp. jegathesan and the d ifferent B. thuringiensis subsp. israelensis resistant mosquito strain s were low, ranging from 2.3 to 5.1. However, the levels of cross-resi stance to Cry11B were much higher and were directly related to the com plexity of the B. thuringiensis subsp. israelensis Cry toxin mixtures used to select the resistant mosquito strains. The LC95 RR obtained wi th the mosquito strains were as follows: 53.1 against Cq4D, which was resistant to Cry11A; 80.7 against Cq4AB, which was resistant to Cry4A plus Cry4B; and 347 against Cq4ABD, which was resistant to Cry3A plus Cry4B plus Cry11A. Combining Cyt1A with Cry11B at a 1:3 ratio had litt le effect on suppressing Cry11A resistance in Cq4D but resulted in syn ergism factors of 4.8 and 11.2 against strains Cq4AB and Cq4ABD, respe ctively; this procedure eliminated cross-resistance in the former mosq uito strain and reduced it markedly in the latter strain. The high lev els of activity of B. thuringiensis subsp. jegathesan and B. thuringie nsis subsp. israelensis, both of which contain a complex mixture of Cr y and Cyt proteins, against Cry4- and Cry11-resistant mosquitoes sugge st that novel bacterial strains with multiple Cry and Cyt proteins may be useful in managing resistance to bacterial insecticides in mosquit o populations.