Ultrastructural and immunocytochemical studies were carried out in the tail region of spermatids and spermatozoa of the phytophagous bugs, Acrosternum aseadum and Euchistus heros, The axoneme presented a 9+9+2 microtubule pattern and bridges occurred between axonemal microtubules 1, 5, and mitochondrial derivatives. Two paracrystalline structures, embedded in an amorphous matrix, were observed in the mitochondrial derivatives. The axonemal microtubules contained alpha, acetylated and tyrosinated tubulin. Cytoplasmic microtubules contained alpha, beta and gamma tubulin. Moreover, the gamma tubulin was detected near the electron dense rod, an element associated with the centriole, suggesting that this structure may be a microtubule organizing center.4041700163170