Abstract
Abstract The results of a survey of insecticide resistance in the cotton whitefly (Bemisia tabaci Genn.) to some of the commonly used insecticides, or insecticide mixtures, in the Sudan Gezira Scheme, disclosed that high levels of resistance exist in the Scheme's whitefly populations. The resistance ratios of the scheme populations, relative to a susceptible strain, for the adults and nymphs, respectively were as follows: dimethoate, 454 × and 257 ×; endosulfan, 364 × and 5 ×; dimethoate/endosulfan mixture, 10 × and 7 ×; methomyl, 8 × and 8 ×; amitraz, 6 × and 2 ×; and amitraz/endosulfan mixture, 5 × and 3 ×. The adults of an out‐of‐season strain of the cotton whitefly exhibited moderate levels of resistance to amitraz (7 ×), amitraz/endosulfan mixture (3×), and endosulfan (3×). The nymphs of this strain showed resistance to dimethoate (25 ×), amitraz (8 ×) and dimethoate/endosulfan mixture (3 ×). Adult whiteflies were always found to be more susceptible than nymphs and the resistance ratio of the adults was generally higher than that of the nymphs.
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