Apart from humans, many organisms acquire beneficial bacterial partners from the food that they eat. But what about generalists, whose diet can vary every day? We asked whether the bacteria in the diet of the red flour beetle – a grain pest found across the world – impact the beetles’ fitness in different diets. For these beetles, flour is not only their diet, but also the environment in which they live. Aparna found that beetles derive many fitness benefits from microbes in wheat flour, which they have used for many generations. But microbes from the new diets are not important for beetle fitness. So, diet shifts can be problematic for generalists, because their bacterial partners may be missing. Read the paper here.