Complex unsuitable weather conditions as a key stressor for insect populations in the temperate zone

Insects in temperate regions exhibit tightly regulated life cycles, with overwintering occurring in distinct developmental stages that are physiologically adapted to low temperatures. During the vegetation period, phenological processes such as hatching, mating, and larval development are likewise strongly influenced by ambient weather conditions. The pronounced synchrony of long-term trends in insect biomass across diverse habitats suggests that weather patterns and associated anomalies constitute major drivers of population dynamics. We identified a priori life-history phases expected to be particularly sensitive to climatic variability and quantified corresponding weather conditions and anomalies for each period. Incorporating these variables, we modelled variation in insect biomass using 27 years of data. The findings reinforce previous results indicating that, in addition to cold and wet summers, particularly warm and dry winters exert pronounced negative effects on insect populations. Using only the weather variables from our model, we were able to predict insect biomass in independent validation datasets with substantial accuracy. Our results indicate that weather conditions and anomalies represent an underappreciated yet highly influential component in the ongoing discourse on insect decline. For rare species, population reductions driven by adverse weather over decadal time scales may plausibly contribute to local extirpations, especially in small and fragmented habitats where compensatory colonization–extinction dynamics, as posited by metapopulation theory, are constrained by the high spatial and temporal synchrony of weather conditions. Given that many species have not yet adapted to rapid climatic shifts, the conservation implications are considerable: maintaining and restoring extensive, high-quality habitats capable of supporting demographically viable populations appears to be the most effective buffer against increasing climatic unsuitability. Together with previous findings, our results suggest a complex interplay in which suitable weather conditions primarily influence overall population biomass, whereas land-use strongly shapes species composition and diversity. Furthermore, these findings underline that insect biomass—being driven by factors distinct from those shaping diversity—should not be used as a surrogate for insect diversity but rather as an indicator of insect population wellbeing more generally.