Our long-term goal is to develop an economically competitive biological control program for twospotted spider mites (TSM), Tetranychus urticae Koch in greenhouses. Presently the most effective way to achieve biological control of TSM is through frequent inundative releases of the predatory mite, Phytoseiulus persimilis Athias-Henriot. However, because this tactic is costly and labor intensive, it has met with resistance in commercial greenhouses. Therefore, increasing natural enemy efficiency is a priority for researchers. To accomplish this goal we used genetic selection to achieve lines of predators exhibiting high levels of response to life-history traits, including prey consumption and conversion efficiency (ability to convert prey to offspring). After 5 cycles of selection, we were able to double the consumption rate from 25.16 ± 4.56 to 42.1 ± 1.05 prey eggs per 24 h. We were also able to increase the conversion efficiency from 0.13 ± 0.03 to 0.25 ± 0.03 predator offspring per prey egg consumed in 24 h. In greenhouse experiments, we evaluated pest suppression on lima bean plants caused by the selected predator lines and an unselected line at two spatial scales: within a single plant (no emigration); between two plants (allowing emigration). Plants were destructively sampled every third day for four weeks. At both spatial scales, the selected predator lines caused significantly greater suppression of TSM populations compared to the unselected line. Of the two selected lines, consumption line was more effective in reducing TSM than conversion efficiency line although there were fewer predators produced in the consumption line.