In Hemilepistus reaumuri (Audouin, 1826), a monogamous desert isopod, control of reproduction by external factors is studied in females from a Tunisian population. In the wild, females perform only one brood (in May). In contrast to isopods submitted to temperate climates (long day species), H. reaumuri is unsensitive to photoperiod. Onset of reproduction is dependent on temperature: it occurs only when temperature is higher than 15°C (between 15°C and 20°C). Moreover, at 25°C, the lag time of the onset of reproduction is shortened by 50% in comparison with the delay obtained at 20°C. Whereas an isolated female remains in sexual rest, the presence of a male (even separated from the female by a wire netting) speeds up vitellogenesis following by moult. The beginning of burrow digging is well correlated with the initiation of reproduction (second phase of vitellogenesis).