Insect symbionts offer an opportunity to deal with the anticipated elevated demand for novel pest management strategies. One approach is the disruption of essential symbionts required by the pests. In the present study, we examined the effects of symbiont elimination strategies, high temperature and sterilization agents, on the fitness of three stink bugs, Brachynema germari Kolenati, Acrosternum heegeri Fieber, and Acrosternum arabicum Wagner by using demographic approach. In the high-temperature experiments, almost all insects exhibited severe fitness defects, including elevated nymphal mortality and reduced population growth parameters (especially intrinsic rate of increase, r), as well as significant reductions in the gut symbiont titers. In the egg surface sterilization assays, we experimentally assessed the effects of sterilization agents on the bugs and their symbionts and observed similar fitness defects to those observed under the high-temperature condition. According to the results, we concluded that the host's defective phenotypes are attributable not to the heat stress itself but to the suppression of the symbiont titer, which highlights the possibility that global warming and elevated temperature may negatively affect this mutualism.Together, the results suggest the biological importance of the bacterial symbiont for the host that might help us for better management of these important pests in the future.