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The effect of ingredients of seed kernels of the neem tree (Azadirachta indica) on nymphs of locusts and grasshoppers were studied in laboratory, semi-field and field trials in Africa, Germany and Madagascar. There was a very strong phagorepellent effect of neem oil on the desert locust, Schistocerca gregaria, and on the red locust, Nomadacris septemfasciata. The same applied to the variegated grasshopper, Zonocerus variegatus. On the other hand, the African migratory locust, Locusta migratoria migratorioides, was repelled from neem-oil treated food to a much lesser extent than the other species. Morphogenetic defects on antennae, legs and wings were often observed on nymphs and adults of S. gregaria and to a somewhat lesser extent of Z. variegatus and L. m. migratorioides. Slight effects occurred in N. septemfasciata. Solitarization effects on gregarious nymphs, e.g. green colour, mainly occurred in S. gregaria, also reduction of fitness. The highest mortality after topical application was recorded in S. gregaria and Z. variegatus, after intake of neemcontaminated food in L. m. migratorioides and Z. variegatus. Neem oil and other products (aqueous seed kernel extracts, neem seed powder) can be used for controlling some important locust and grasshopper species in farmers’ fields with good success.