Pre-selecting resistance against individual Bti Cry toxins facilitates the development of resistance to the Bti toxins cocktail

• Pre-selection of Cry resistance facilitates Bti resistance development in mosquitoes.
• Strains resistants to each Bti Cry toxins exhibit cross-resistance to each Cry toxin.
• At least two mechanisms of resistance are developed against Cry4Aa and Cry4Ba/Cry11Aa.

The bioinsecticide Bacillus thuringiensis subsp. israelensis is a larvicide used worldwide for mosquito control, which contains three Cry toxins and one Cyt toxin. We investigated for the first time in Aedes aegypti (1) the evolution of resistance and cross-resistance of strains selected with each Cry toxin, and (2) the effect of pre-selection with Cry toxin on the evolution of resistance to a mix of Bti toxins. Cross resistance was higher between Cry4Ba and Cry11Aa than between Cry4Aa and either Cry4Ba or Cry11Aa, suggesting both common and specific mechanisms of resistance. Pre-selecting resistance to each Cry toxins facilitated the development of resistance to the full Bti toxins cocktail.

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