Studies on the proteolytic processing and binding of Bt toxins Cry3Bb1 and Cry34Ab1/Cry35Ab1 in the midgut of Western corn rootworm (Diabrotica virgifera virgifera LeConte)

The Western corn rootworm (WCR) is one of the most economically important corn pests worldwide. One possibility for controlling this pest is the cultivation of Bt-corn. However, widespread cultivation of Bt-corn may increase the probability of the development of pest populations resistant to the respective Bt toxins. To establish test systems for identifying resistance mechanisms in the case of resistance development, different parameters involved in the processing of Bt toxins in the midgut of third instars larvae of WCR (European strain) were studied. The proteolytic processing of Bt toxins Cry3Bb1 and Cry34Ab1/Cry35Ab1 by WCR midgut juice was examined, but no degradation of any of these toxins was observed. Ligand-blot binding analyses with Cry3Bb1 as well as Cry34Ab1 and Cry35Ab1 revealed specific receptors in the WCR midgut epithelium. The molecular weights for Cry3Bb1, Cry34Ab1, and Cry35Ab1 receptors were characterized as having molecular weights of approximately 30 kDa, 110 kDa, and 50 kDa, respectively.