Abstract: Social evolution theory makes a number of predictions about how bacterial virulenceevolves in different environments and can have important implications for how we maintain orimprove the virulence of biopestidical bacteria such as B. thuringiensis. Investment in virulenceshould not favoured in homogeneous artificial media, since social “cheats” that fail to synthesizevirulence factors should be at growth advantage. There is some evidence that biopesticide derivedstrains are attenuated with respect to wild-type relatives. Selection of rifampicin resistant mutants ofB. t. kurstaki in the diamondback moth Plutella xylostella led to increases in virulence and alsoreduced growth rates in artificial media, as predicted by theory.