Temperature at parental generation affects bacterial communities associated with offspring for both host and parasitoid.

The thermal conditions experienced during development can affect host-associated microbial communities. We still know little about whether such effects similarly persist across life stages between different species. In particular, it is unclear if the bacterial communities of closely interacting species, such as hosts and their endoparasitoids, exhibit similar responses to thermal conditions. We reared two generations of the Melitaea cinxia butterfly and its specialised parasitoid wasp, Hyposoter horticola, at three temperatures in the laboratory (26°C, 28°C, and 31°C). We found that the two species harbour different bacterial communities as adults, with the parasitoid exhibiting higher bacterial richness than its host butterfly. When the parental generation of the butterfly was exposed to high temperatures, the F1 generation exhibited increased bacterial richness but a reduced diversity (Shannon index). The opposite effect was observed for its parasitoid, but only for the wasps infected with Wolbachia, which appears sensitive to thermal conditions. Collectively, these results highlight that the bacterial communities of insect hosts and their parasitoids are distinct units, differently susceptible to environmental thermal conditions, particularly to temperatures experienced at the parental generation.