In the EU-project SAFEHOUSE one objective is to develop alternative control methods against poultry red mites based on a combination of inert dusts and mite-pathogenic fungal isolates. Both components have some pathogenicity to the mites. However, the question is whether a combination of the two components might produce a synergistic effect as seen in other arthropods. As a first step, the effects of a range of inert dust formulations were evaluated in the laboratory at different doses and at different levels of air humidity. The results have shown major variations in the speed of kill but also in the repellency of the different formulations, and both parameters vary with the dose and the air humidity.