Digest: Winter is coming: overwintering selection and the cost of insecticide resistance in fruit flies

Do winter conditions drive rapid adaptation in insects, and does prior selection for insecticide resistance constrain it? To test these questions, Prileson et al. (2026) exposed replicate Drosophila populations to an outdoor overwintering period and tracked traits before and after in common gardens. Control populations that had not been previously exposed to insecticides showed consistent shifts in body size and fecundity, indicating rapid adaptation. Resistant populations suffered higher winter mortality, and both control and resistant populations were more susceptible to insecticides after overwintering, indicating a trade-off between resistance and overwintering performance.