Endocrine and neuroendocrine effects of Azadirachtin in adult females of the earwig Labidura riparia.

In previous studies we have shown that injection of the insect growth regulator Azadirachtin (AZA) into young vitellogenic females induces inhibition of vitellogenesis in a dose-dependent manner. Juvenile hormone treatment rescues vitellogenin synthesis and ovarian growth. The cytopathological effects on ovaries and fat body are not linked to an inhibition of feeding. In this work we investigated the effects of AZA on the endocrine and neuroendocrine system. Enzyme immunoassay reveals that ovarian ecdysteroid levels are drastically reduced, in a dose-dependent fashion, by AZA. Ultrastructural study indicates that corpus allatum cells exhibit signs of inactivity and degenerative changes after AZA exposure. Using an antibody against allastostatin-3 of Blatella germanica (BLAST-3), we show the appearance of strong immunoreactivity of numerous cells and axons in the brain of AZA-injected females. We conclude that vitellogenesis inhibition by AZA consists of a direct cytotoxic effect as well as a generalized disruption of endocrine and neuroendocrine functions.