Receptors are affected by selection with each Bacillus thuringiensis israelensis Cry toxin but not with the full Bti mixture in Aedes aegypti

Abstract

Bacillus thuringiensis israelensis (Bti) toxins are increasingly used for mosquito control, but little is known about the precise mode of action of each of these toxins, and how they interact to kill mosquito larvae. By using RNA sequencing, we investigated change in gene transcription level and polymorphism variations associated with resistance to each Bti Cry toxin and to the full Bti toxin mixture in the dengue vector Aedes aegypti. The up-regulation of genes related to chitin metabolism in all selected strain suggests a generalist, non-toxin-specific response to Bti selection in Aedes aegypti. Changes in the transcription level and/or protein sequences of several putative Cry toxin receptors (APNs, ALPs, α-amylases, glucoside hydrolases, ABC transporters) were specific to each Cry toxin. Selective sweeps associated with Cry4Aa resistance were detected in 2 ALP and 1 APN genes. The lack of selection of toxin-specific receptors in the Bti-selected strain supports the hypothesis that Cyt toxin acts as a receptor for Cry toxins in mosquitoes.