Comparative histopathology of two novel bacterial insecticidal proteins in Tenebrio molitor and Diabrotica virgifera virgifera larvae

Larvae of the Western corn rootworm (Diabrotica virgifera virgifera) are the most devastating pest of corn in the US.  Due to reports of field-evolved resistance, novel insecticidal proteins are needed as alternative candidates for expression in transgenic corn to control this insect pest.  A novel insecticidal protein from a Gram negative bacterium (toxA) and a Cry-derived protein (toxB) have been identified and developed, respectively, as candidates for expression in transgenic corn targeting larvae of D. v. virgifera.  In this work, we used Tenebrio molitor larval midgut as a model to characterize toxin binding and histopathology of toxA and toxB proteins in coleopteran larvae, and then compared to histopathology in D. v.virgifera larval midguts.  While both toxins bound to the midgut brush border membrane, differences observed in H&E stained histological sections and TUNEL assays support differences in the mode of action of these toxins in coleopteran larvae.