Mode of action of mosquitocidal Bacillus thuringiensis toxins

Cry toxins from Bacillus thuringiensis (Bt) are used for insect control. Their primary action is to lyse midgut epithelial cells. In lepidopteran insects, CrylA monomeric toxins interact with a first receptor and this interaction triggers toxin oligomerization. The oligomeric structure interacts then with a second GPI-anchored receptor that induces insertion into membrane microdomains and larvae death. In the case of mosquitocidal Bt strains, two different toxins participate, Cry and Cyt. These toxins have a synergistic effect and CytlAa overcomes Cry toxin-resistance. We will summarize recent findings on the identification of Cry receptors in mosquitoes and the mechanism of synergism: CytlAa synergizes or suppresses resistance to Cry toxins by functioning as a Cry membrane-bound receptor. (c) 2006 Elsevier Ltd. All rights reserved.