the development (egg-adult) of bemisia tabaci (genn.) b-biotype (=bemisia argentifolii, bellows & perring), was studied in field conditions and in incubators at constant temperatures (15, 20, 25, 30 and 35±1oc), using soybean, glycine max (l.) merrill, msoy 8001, as host plant. the temperatures threshold (tb) and the thermal constant (k) for egg, nymph and life cycle (egg-adult) were 11.1oc / 98.8 degree-days; 6.8oc / 383.8 degree-days and 8.3oc / 472.6 degree-days, respectively. at the temperatures of 15oc and 35oc, insect viability was smaller. in the field, 70% of the adults emerged after 413,2 degree-day were accumulated. the degree-day pattern used was adequate for the previewing bemisia tabaci b-biotype adult occurrence in field, and it can also be used to determine the number of generations in different areas of the country.