Ultrastructural changes in the corpus allatum after azadirachtin and 20-hydroxyecdysone treatment in adult females of Labidura riparia (Dermaptera)

Abstract

In previous reports, we have shown that the injection of azadirachtin (AZA) as well as 20-hydroxyecdysone (20E) into vitellogenic females of Labidura riparia induces inhibition of vitellogenin synthesis and ovarian development. Juvenile hormone (JH) treatment rescues vitellogenin synthesis and ovarian growth (Sayah et al., 1995, 1996). In this work, we have studied ultrastructural changes of corpus allatum (CA) after injection of 200, 400, and 600 ng of 20E or 1, 3, and 5 μg of AZA. CA cells exhibit signs of inactivity in both AZA and females treated with 20E at doses of 3 μg and 400 ng, respectively. Conspicuous cytological effects consisting of multivesicular bodies with dense contents, abnormally large intercellular spaces comprising myelinic structures, and rare smooth endoplasmic reticula occured in cytoplasm of CA glandular cells in both experimental females. However, the CA ultrastructure of females injected with 20E differs from CA cells of females injected with AZA in having a cytoplasm containing numerous electron-lucent intracellular areas and marked glycogen zones. They also differ in having abundant microtubules and well-developed junctional membranes. At a dose of 600 ng of 20E or 5 μg of AZA, the intensity of the cytotoxic effects is more apparent. CA cells display pycnotic nuclei, spherical mitochondria, large multivesicular bodies, and vacuolization of the cytoplasm. These results are discussed and compared with observations made on other insect species.