Resistance to methamidophos in the Pakistani populations of cotton whitefly, Bemisia tabaci was monitored continually from 1992 through 2000 using a leaf-dip method. A very high methamidophos resistance was encountered from 1992 to 1996. This resistance then fell sharply during 1997 to 1999 until the whitefly populations almost reverted to susceptibility in the year 2000. This reversion was mainly attributed to a major replacement of methamidophos by novel chemistries for whitefly control and adoption of better insecticide resistance management practices by the farmers. A rotation of effective chemistries, with different modes of action, along with the exploitation of non-chemical control methods for whitefly is recommended to prevent the development of resistance to methamidophos and other compounds.