Laboratory bioassays were conducted to evaluate the susceptibility of seven populations (strains) of the confused flour beetle, Tribolium confusum Jacquelin du Val (Coleoptera: Tenebrionidae), to five commercially available diatomaceous earth (DE) formulations: Insecto, Protect-It, Protector, PyriSec, and SilicoSec. These DEs were applied on wheat, Triticum durum Desf., at two dose rates, 500 and 1000 ppm. The six beetle strains were obtained from Denmark, United Kingdom, Greece, Germany, Italy, and Portugal, whereas a seventh strain came from the Greek strain after laboratory selection with SilicoSec-treated wheat for six generations. Adults of the above-mentioned strains were exposed for 7 d to wheat treated with each DE formulation, and mortality was assessed after exposure. For all DE–dose combinations, significant differences were noted in mortality levels among strains. Generally, the strains from Denmark, United Kingdom, and Germany were the most susceptible to the DEs used, whereas the strain from Portugal was the least susceptible. No significant differences were noted in susceptibility level between the initial Greek strain and the laboratory-selected Greek strain, with the exception of Protector, where the selected strain was significantly more tolerant than the initial strain for both dose rates tested.