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Toxicity of n-hexane and methylene chloride extracts of Azadirachta indica, Citrullus colocynthis, Ammi majars and Mentha microphylla was evaluated against the newly moulted instar nymph of desert locust Schistiocerca gregaria (Forsk). Leaves dip bioassays were used to obtain concentration-mortality data. Treatments of nymphs for 7 and 14 days, leading to calculation of LC50 and LC90 values. A wide range in LC50 and LC90 values was exhibited among the tested extracts. After 14 days of feeding, the product of A. majus with methylene chloride solvent was most active against 2nd instar nymph (LC50=25.13 mg ml(-1)), followed by C. colocynthis (LC50=39.92 mg ml(-1)), A. majus (LC50=66.78 mg ml(-1)) and M. microphylla (LC50=70.35 mg ml(-1)). Formulated extracts were investigated by two non-ionic surfactants and two blended emulsifiers. After formulations with sodium sulphonate as emulsifier, methylene chloride extracts of A. indica substantially increased nymphal mortality, reduced nymphal weight, exhibited adverse morphogenic effects and raised nymph duration period. Moreover, prolonged exposure to 100 mg ml(-1) of formulated extracts of A. indicia and C colocynthis decreased effect on hemolymph total protein, total lipids and glucose contents as well as, on ALAT activity of the studied nymph. These results document the potential of botanical formulations of A. indicia and C. colocynthis with sodium sulphonate as emulsifier may prove to be a probable candidate for development of biopesticides to control desert locust,.