Inhibition of Oogenesis and Ovarian Ecdysteroid Synthesis by Azadirachtin in Locusta migratoria migratorioides (R. & F.)

The sterilizing effect of azadirachtin, an insect growth regulator from the neem tree, Azadirachta indica A. Juss, was tested with mature females of Locusta migratoria. After a single injection of 10 μg into females between 2 and 13 days after emergence, about 60% died during the following four days and all lost weight in the range of about 50%. If the compound was injected into animals of an age between 2 and 10 days, no maturation of the terminal oocytes could be observed. Injection at an age between 10 and 13 days after adult emergence resulted in ovaries which contained almost mature oocytes. Most of the treated locusts had no oviposition and only traces of ecdysteroids were present in their ovaries, as quantified by radioimmunoassay. The inhibition of oogenesis and of ovarian ecdysteroid synthesis by azadirachtin is discussed on the basis of its interference with the neuroendocrine control of hormone synthesis.