Oligomerization is a key step in Cyt1Aa membrane insertion and toxicity but not necessary to synergize Cry11Aa toxicity in A edes aegypti larvae

B acillus thuringiensis produces insecticidal C ry and Cyt proteins that are toxic to different insect orders. In addition, Cyt toxins also display haemolytic activity. Both toxins are pore‐forming proteins that form oligomeric structures that insert into the target membrane to lyse cells. Cyt toxins play an important role in mosquitocidal activity since they synergize C ry toxins and are able to overcome resistance to C ry toxins. C ry and Cyt toxins interact by specific epitopes, and this interaction is important to induce the synergistic activity observed. It was proposed that Cyt toxins do not interact with protein receptors but directly interacting with the specific midgut cell lipids. Here, we analysed if oligomerization and membrane insertion of C yt1Aa are necessary steps to synergize Cry11Aa toxicity. We characterized Cyt1Aa helix α‐ C mutants that were affected in oligomerization, in membrane insertion and also in haemolytic and insecticidal activities. However, these mutants were still able to synergize Cry11Aa toxicity indicating these steps are independent events of Cyt1Aa synergistic activity. Furthermore, the data indicate that formation of stable Cyt1Aa ‐oligomeric structure is a key step for membrane insertion, haemolysis and insecticidal activity.