The cold hardiness and overwintering potential of the southern African pirate bugs, Orius thripoborus (Hesse) and Orius naivashae (Poppius) (Hemiptera: Anthocoridae), were assessed in the laboratory. Diapause traits were studied by observing nymphal development and reproductive performance of adults at 18 °C and three photoperiods (10:14, 12:12 and 14:10 (L:D) h). A 12 h light regime was also tested at 23 °C. A 12 h photoperiod and 18 °C induced reproductive diapause in 84 and 42 % of O. naivashae and O. thripoborus females, respectively. Cold tolerance of adults was measured by determining the supercooling point (SCP, the temperature at which the insect’s body fluids freeze) and lethal time (LT₅₀, the time required to kill 50 % of the population) at 0 and 5 °C. All observed SCPs ranged from −21 to −17 °C. Significantly lower SCP values were observed for acclimated (seven days at 10 °C) O. naivashae females. LT₅₀-values averaged 6.4 and 4.4 days at 0 °C and 11.6 and 7.8 days at 5 °C, for adults of O. thripoborus and O. naivashae, respectively. The findings indicate that O. naivashae is less cold tolerant and has a higher diapause incidence compared with O. thripoborus. Therefore, the latter species may have better potential for use in biological control programmes in the cooler regions of southern Africa or elsewhere.