The histopathological effects of the spore-crystal complex of indigenous Bacillus thuringiensis (Bt) isolate, as well as Cry 2Ab gene expressed in transgenic tomato plants on the midgut of 4th instar larva of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidea) has been investigated using the transmission electron microscope (TEM). Remarkable ultrastructural changes were observed in the columnar and goblet cells of the larval midgut after feeding on either transgenic tomato leaves, or spore-crystal complex of Bt. The effects observed included breakdown of microvilli of epithelial cells, increase in the electron density of the cytoplasm and vacuolation associated with different sizes of lysosomes; interruption of the goblet cells and distorted goblet cavities which lost their cytoplasmic projections; destruction of the mitochondria which lost their cristae; degeneration of the endoplasmic reticulum; collapse of the nucleus associated with rupture of nuclear envelope and clumped chromatin. Feeding the larvae on transgenic Bt-tomato plants caused in addition to the aforementioned changes severe vacuolation and degeneration of the nucleus in both columnar and goblet cells and the nuclear membrane was broken into electron dense ring spheres.
Keywords: Bt-tomato; Helicoverpa armigera; Histopathology; Midgut; TEM.