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1. Investigations on S. gregaria were carried out first in the laboratory on insects reared under laboratory conditions, as well as in laboratory and field studies on locusts collected in the Tamesna Desert (Republic of Niger).

2. Both groups were treated topically with various neem product formulations or injected with azadirachtin.

3. Enriched neem oil sprayed on flying S. gregaria increased its mortality rate up to 75% within 10 days.

4. The treatment with neem oil generally decreased the flight performance substantially up to 70%.

5. A recovery from this reduced fitness could not be observed within 3 months.

6. In contrast to these results untreated and palm oil-treated controls, azadirachtin injected locusts, and locusts sprayed during resting phases did not show a mortality rate higher than 8%.

7. Injection of synthetic adipokinetic hormone did not raise the blood lipid concentration in neem-treated S. gregaria nearly as much as it did in untreated controls and azadirachtin-injected locusts.

8. Therefore, it can be assumed that compounds of the neem seed kernels inhibit the lipid-mobilizing system of S. gregaria.

9. Consequently, the locusts treated with neem products are too short on "fuel" to cover long distances.