Transgenerational decline in Wolbachia density in Culex pipiens after thermal stress

Wolbachia pipientis is a widespread maternally inherited endosymbiont in arthropods, including Culex pipiens, and plays a crucial role in vector biology and pathogen interference. However, the stability of Wolbachia infections is temperature-sensitive, with elevated environmental temperatures known to reduce bacterial density. This study investigates the transgenerational effects of high-temperature exposure on Wolbachia density across multiple generations of Cx. pipiens reared under thermal stress. We established parallel mosquito colonies maintained at 25°C (control) and 40°C (heat stress) for four consecutive generations. Relative Wolbachia density was measured at each generation by qPCR against the wsp gene and normalized to host genomic DNA. Wolbachia titer levels were also monitored throughout the experiment to identify trends and potential changes in symbiont-host dynamics over time. The study sought to explore whether long-term thermal stress could influence the maintenance and stability of Wolbachia infection over generations, as well as gain a better understanding of the long-term influence of environmental temperature on symbiont-host interactions. These findings contribute to a growing line of research into the effect of abiotic stressors on symbiotic relationships in vector populations. The results are placed into context relative to Wolbachia-driven vector control programs, particularly where there is increased temperature variation under climate change. Understanding how thermal stress affects Wolbachia density over generations can be applied toward informing and sustaining the sustainability of biological control programs in the field.