THE BACILLUS-THURINGIENSIS VEGETATIVE INSECTICIDAL PROTEIN VIP3A LYSES MIDGUT EPITHELIUM-CELLS OF SUSCEPTIBLE INSECTS

The Vip3A protein is a member of a newly discovered class of vegetativ e insecticidal proteins with activity against a broad spectrum of lepi dopteran insects. Histopathological observations indicate that Vip3A i ngestion by susceptible insects such as the black cutworm (Agrotis ips ilon) and fall armworm (Spodoptera frugiperda) causes gut paralysis at concentrations as low as 4 ng/cm(2) of diet and complete lysis of gut epithelium cells resulting in larval death at concentrations above 40 ng/cm(2). The European corn borer (Ostrinia nubilalis), a nonsuscepti ble insect, does not develop any pathology upon ingesting Vip3A. While proteolytic processing of the Vip3A protein by midgut fluids obtained from susceptible and nonsusceptible insects is comparable, in vivo im munolocalization studies show that Vip3A binding is restricted to gut cells of susceptible insects, Therefore, the insect host range for Vip 3A seems to be determined by its ability to bind gut cells. These resu lts indicate that midgut epithelium cells of susceptible insects are t he primary target for the Vip3A insecticidal protein and that their su bsequent lysis is the primary mechanism of lethality, Disruption of gu t cells appears to be the strategy adopted by the most effective insec ticidal proteins.