Biological control agents (BCA) are often mass reared at conditions very different from those at which they have to provide their service, especially if they are to be used under field conditions. It has been suggested that biocontrol efficiency might be enhanced by acclimating the BCA under near-field conditions for some time before release (beneficial acclimation hypothesis), and some studies (e.g. with ladybirds) have supported this idea. We reared Orius majusculus, a commercially available BCA, at three temperatures (12, 16 and 20 °C) throughout the whole development. The predation capacity for rosy apple aphids (Dysaphis plantaginea) of females from each of these treatments was tested at the same temperatures (12, 16 and 20 °C). Additionally, we tested the effects of low temperature treatment only during the last nymphal instar, to examine if shorter treatments would have the same effects. Our results rejected the positive acclimation hypothesis. At all test temperatures predation capacity was highest for females that had developed at 20 °C and lowest for those that had developed at 12 °C. Thus, development at low temperatures had a detrimental effect on predatory performance (negative acclimation effect) at both high and low temperatures, and the effect was larger the longer the treatment. Mortality of the nymphs was also increased at lower temperatures. Thus, no enhanced biocontrol efficiency or production benefits were gained from low temperature treatment of O. majusculus, neither as full developmental treatment nor as a short term treatment.