Binding of the Bacillus sphaericus (Eubacteriales: Bacillaceae) toxin to midgut cells of mosquito (Diptera: Culicidae) larvae; relationship to host range

Fluorescent-labelled Bacillus sphaericus (Neide) toxin was found to bind to sharply delineated regions of the proximal lobes of the gastric caecum and the posterior midgut of susceptible Culex quinquefasciatus Say larvae but did not bind to midgut cells of resistant Aedes aegypti (L.) and A. triseriatus (Say) larvae. Failure of this toxin to bind to midgut cells or certain mosquito species may be responsible for the restricted host range of B. sphaericus . The toxin appeared to enter the cells of C. quinquefasciatus larvae by receptor-mediated endocytosis, and it accumulated in the cells in bright fluorescent endocytic vesicles.