Ultrastructural and immunocytochemical studies were carried out on spermiogenesis in two species of phytophagous bug, Acrosternum aseadum and Nezara viridula. The nucleus development involved changes in the shape and in the degree sf chromatin condensation, with specific aggregation patterns of DNA-histone complex occurring during this process. The acrosome showed a three-layered and the acrosomal content a paracrystalline arrangement. The axoneme presented a 9+9+2 microtubule pattern and bridges occurred between axonemal microtubules 1 and 5, and mitochondrial derivatives. Two paracrystalline structures embedded in amorphous regions were observed in the mitochondrial derivatives. The use of the negative staining technique shows a zig-zag profile in the mitochondria due to infolding to the cristae, regularly spaced with approximately 40 nm. An electron dense rod was observed near the centriolar adjunct; it presented labelling for tubulin suggesting that this structure may be involved in the microtubule organization during spermiogenesis of these insects.304485493