Insecticide resistance in Egyptian strains of Bemisia tabaci

A strain of Bemisia tabaci ('B'-biotype) collected from cotton and vegetable crops at the beginning of the growing season in Egypt displayed marked resistance to a carbamate (carbosulfan) and moderate resistance to a pyrethroid (cypermethrin). It displayed no resistance to an organophosphate (profenofos) or to the neonicotinoid imidacloprid. Another strain, collected at the end of the growing season from the same location, differed markedly in its response. In this strain, resistance to carbosulfan remained high but resistance to profenofos and cypermethrin increased. Slight resistance to imidactoprid was detected. Neither strain showed resistance to the insect growth regulator pyriproxyfen. The resistance profiles of these strains Were compared to that of a typical Israeli field strain ('Q' biotype) and are discussed with reference to their collection date and the patterns of insecticide use in those countries. The ability of Egyptian `B' biotypes to introgress with Israeli `Q'-biotypes was examined, and the resistance characteristics of the resulting offspring were investigated. The consequences of introgression between co-existing biotypes with different resistance profiles are considered.