The sudden outbreaks of sweetpotato whitefly Bemisia tabaci (Genn.) on cotton, vegetable crops, ornamental and medical plants in Egypt through the last few years and the surgence of the pest as a major pest and virus vector, prompted investigation into the variation among whitefly populations in developmental biology, behaviour, host expansion, growth statistics and insect interactions on a wide basis. Recent studies have also prompted a renewed interest in the concept of biotypes of B. tabaci. The coincidental emergence of the so called new poinsettia strain "B" biotype or the new species Bemisia argentifolii (Pellows & Perring) and resulting impact on agricultural productivity have also reaffirmed the need to understand more about fundamental differences among populations of B. tabaci. Biological and ecological procedures, i.e., thermobility coefficients, thermal require-ments and age specific survived and fecundity parameters, were used to determine these variations among populations of various hosts and locations in Middle Egypt.

Results suggest that whiteflies are of two groups but recently derived from the same source. The data also verify the occurrence of the strain "B" in Middle Egypt agricultural areas.

The implications of this introduction on virus epidemiology and crop production in those areas are discussed.