Abstract: Environmental conditions in a protected crop can vary widely depending on weather, season, geographic location, crop type and cropping structure. The establishment of a predatory mite population and its efficacy at controlling the target pest depend on the environmental conditions in the crop. Temperature and relative humidity (RH) are important factors influencing the population increase of the predator and therefore the numerical advantage over the pest. Predatory mite breeding sachets spend several weeks in a crop and their performance will be affected by abiotic factors, thus impacting the predator output from the sachet. In order to investigate the impact of temperature and RH on predator release, sachet trials were conducted under controlled environmental conditions comparing constant temperature and RH at different levels. Amblyseius swirskii breeding sachets, with Suidasia medanensis as prey, were placed on sticky traps which were changed three times per week for five weeks. Temperature and RH were found to influence the predator release profile and the total number of mites released, indicating that the performance of a breeding sachet not only depends on its initial composition but also the climatic conditions in the target crop.