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Resistance in the cotton whitefly, Bemisia tabaci (Genn.), to insecticide recently introduced into Sudan Gezira Abstract. A survey for resistance in the cotton whitefly, Bemisia tabaci (Genn.), to chlorfenvinphos, chlorfenvinphos+endosul-fan, methomyl+endosulfan,deltamethrin, and deltamethrin + endosulfan, was carried out during the season 1983/84. On the basis of LC 50 adults and nymphs of the Barakat Block population (Sudan Gezira Board) evolved resistance ratios (RR'S) to chlorfenvinphos (10.5-and 5.61 x); chlorfenvinphos + endosulfan (5-and 4.28 x); deltamethrin (25-and 4.43 x) and deltamethrin + endosulfan (2.5-and 21.68 x), respectively. The study also showed that resistance can spread to neighbouring populations to unexposed insecticides and that resistance can develop to chemicals that have never been applied in the scheme. All three populations showed heterogeneity with regard to their susceptibility to the test insecticides.

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