干旱区生态环境知识资源中心

In laboratory experiments all five nymphal instars of the gregarious phase of the desert locust, Schistocerca gregaria (Forsk.), were sprayed with seed oil from the neem tree, Azadirachta indica (A. Juss.). The doses ranged between 2.5 and 10 l/ha, corresponding ultra low volume application rates for locust control from the air under field conditions. The azadirachtin content of the oil was 0.09 %.

The treated locusts showed high mortality, which often occured during moults, prolonged nymphal development and disturbance of metamorphosis. The latter resulted in morphogenetic defects of eyes, antennae, legs and wings. Practically all adults derived from treated nymphs demonstrated such symptoms. The deformations and/or losses of parts of the legs were the greater the earlier the treatment with neem oil took place during the nymphal development and the higher the dose of neem oil applied. There was also a clear tendency of treated nymphs to solitarization, indicated by the appearance of green hemolymph and brown and green intermediate or solitary forms with - in extreme cases - very little black pigment. An additional moult occurred in numerous treated nymphs, especially after neem oil application during early nymphal instars. In addition, the behaviour of the treated nymphs strikingly changed as they became very sluggish and showed greatly or even totally reduced walking, jumping and climbing abilities. Adults with defect wings were unable to fly.

It is suggested that the above described effects are, at least partly the results of the influence of active ingredients in the neem oil, for instance of azadirachtin, on the hormonal system of the gregarious phase of the desert locust. Endocrinological and other studies are desirable for further clarification of the mode of action.