The toxicity of Bt protoxin mixtures also was tested. All twoprotoxin
mixtures demonstrated a synergistic effect against SSB
larvae (Table 2). In these tests, all LC50 values of Bt protoxin mixtures
were greater than expected values, ranging from 0.08 lg/g
for Cry1Ab/Cry1Ca to 0.84 lg/g for Cry1Ac/Cry1Ba, an 11-fold difference.
In contrast to the synergy of Bt protoxins with SSB, all
but one of the Bt protoxin mixtures demonstrated an antagonistic effect against PSB (Table 2). The exception was the combination of Cry1Aa/Cry1Ab with a SF value of only 1.6. The LC50 values of protoxin
mixtures against PSB ranged from 0.97 lg/g for Cry1Ac/Cry1-
Ca to 63.91 lg/g for Cry1Ac/Cry1Ba, a 66-fold difference.