1- Ecologists have explored widely the consequences of climate change on insect species distribution and fitness. Although most studies have assessed the effect of increasing mean temperatures on individual performances, the response to temporal thermal variations, including the magnitude and frequency of extreme temperatures, has often been overlooked. 2- In the present study, we hypothesized that insect performances increase with increasing mean temperatures but decrease under more variable thermal conditions. We used a manipulative experiment to compare the longevity and weight variation of Monochamus galloprovincialis (Coleoptera: Cerambycidae) under three climatic conditions in which the mean and variance of daily temperatures were both controlled. This insect is vector of the invasive nematode, Bursapheluncus xylophilus, which is the causal agent of the pine wilt disease, one of the major threats to pine forests in Europe. 3- Our results showed that an increase of 2.5 °C in average temperature had no effect on the survivorship and weight variations of the beetle. By contrast, larger fluctuating variations of temperature across year resulted in significantly lower longevity, whereas weight remained unchanged. 4- The results of the present study suggest that the effect of global warming on the survival of M. galloprovincialis is likely to be driven by change in temperature stability rather than by change in mean temperature.