Study of the Bacillus thuringiensis Vip3Aa16 histopathological effects and determination of its putative binding proteins in the midgut of Spodoptera littoralis

The bacterium Bacillus thuringiensis produces, at the vegetative stage of its growth, Vip3A proteins with activity against a broad spectrum of lepidopteran insects. The Egyptian cotton leaf worm (Spodoptera littoralis) is an important agricultural pest that is susceptible to the Vip3Aa16 protein of Bacillus thuringiensis kurstaki strain BUPM95. The midgut histopathology of Vip3Aa fed larvae showed vacuolization of the cytoplasm, brush border membrane destruction, vesicle formation in the apical region and cellular disintegration. Biotinylated Vip3Aa toxin bound proteins of 55- and 100-kDa on blots of S. littoralis brush border membrane preparations. These binding proteins differ in molecular size from those recognized by Cry1C, one of the very few Cry proteins active against the polyphagous S. littoralis. This result supports the use of Vip3Aa16 proteins as insecticidal agent, especially in case of Cry-resistance management.

Vip3Aa16 toxin of Bacillus thuringiensis is active against the polyphagous larvae Spodoptera littoralis with an LC50 of about 305 ng/cm2. After toxin ingestion, midgut cells of treated larvae were disintegrated with vacuolization and vesicles formation compared to a normal aspect of the midgut of non-treated larvae. This effect is due to the presence, in the BBMV of S. littoralis, of two putative binding proteins of the Vip3Aa16 active form with molecular sizes of about 55 and 100 kD.Figure optionsDownload as PowerPoint slideResearch highlights
► Vip3Aa16 toxin of B. thuringiensis is active against the polyphagous larvae S. littoralis with an LC50 of about 305 ng/cm2.
► Midgut cells of Vip3Aa16-treated larvae were disintegrated.
► After activation, the Vip3Aa16 toxin recognizes midgut putative receptors of about 55 and 100 kDa.