The "cotton" strain of Bemisia tabaci and the "poinsettia" strain (A and B, respectively) were compared with respect to rates of water loss at 30 and 40 C at 0% R.H. Critical thermal maxima (CTM's) were determined for the two strains. Metabolic rates (rates of oxygen consumption) were determined for the A and B strains. The relative capabilities of the two strains are discussed and evaluated in light of determination of boundary layer temperatures and relative humidities at under leaf sites. CTM's for each "strain" were ca 54 C where each was acclimated to constant temperatures of 31 C. Rates of water loss in percentages were ca 5-8%/h at 30 C and ca 23%/h at 40 C for A and B . Means were not significantly different for the two "strains." Oxygen consumption (metabolic) rates for the SPW's were ca 7.0 µl/mg/h.