Results
The emergence of adult insect activity is impacted by temperature, precipitation, temperature seasonality, life history traits, and the interactions among these variables (Table 1). Species that diapause as an egg have later emergence dates (approximately 45.7 days) than species that overwinter as adults (Table 1). A one standard deviation (s.d.) increase in temperature (4.77 °C) led to earlier emergence of approximately 12.8 days (95% Bayesian credible intervals (CI) 3.6 - 22.0), but the effects of temperature varied with respect to regional precipitation and human population density values. Compared to areas with high human population density, emergence values are earlier in cool regions with low population density, but later in warm regions with low population density (Figure 3A). Insects in warmer areas emerge earlier than in cool areas, and these phenology shifts are more extreme in wet areas compared to drier areas (Figure 3B). The interaction between temperature and diapause stage, and the interaction between precipitation and voltinism also impacted the emergence of adult insect activity. The emergence of species that diapause as larva or pupa were more sensitive to temperature than species that diapause as adults or eggs (Figure 3C). Univoltine species had earlier emergence in areas with more precipitation, while species that are not univoltine had later emergence in areas with more precipitation (Figure 3D). There was a phylogenetic signal of the random species-specific intercept and the random species-specific slopes of temperature seasonality and precipitation (Supporting Information Figure S2). The partial R2 of our best emergence model was 0.75 (Supporting Information Figure S3).
The top termination model consisted of a set of predictors that included precipitation, temperature seasonality, life-history traits, and the interaction between temperature seasonality and diapause stage (Table 1). A one s.d. increase in precipitation (324 mm) led to a delay in termination of approximately 3 days (95% CI 1.1 - 4.8). Termination of activity was earlier for species that are first observed in spring or summer compared to species that are first observed as adults in fall (Table 1). Additionally, insect species that diapause as larvae terminate adult activity earlier than insects that diapause in other life stages (-18.4, 95% CI -35.8 - -0.7; Table 1). The termination of species that diapause as eggs were the most sensitive to temperature seasonality (Figure 4). Species that spend their immature life stage underground had earlier termination than species that spend their immature life stage in freshwater or aboveground. Detritivores had later terminations than herbivores or carnivores. Phylogenetic signal was again apparent for the species-specific random intercept and species-specific random slope of temperature seasonality and precipitation (Supporting Information Figure S2). The partial R2 of our best termination model was 0.58 (Supporting Information Figure S3).
The top model of adult insect duration was predicted by climate, life history traits, and the interaction between temperature and these other variables. Areas with greater temperature seasonality had shorter durations (Table 1). Additionally, areas with high precipitation had longer durations in warm regions but shorter durations in cool regions (Figure 5A). In contrast to species whose immature habitat is above ground or in freshwater, species whose immature habitat is underground were found to have consistent durations, regardless of whether they were in a warm or cool region (Figure 5B). Diapause stage was again an important trait, with insects that diapause as adults having the longest durations. Conversely, the durations of species that diapause as larvae were the shortest, 44.8 days shorter than species that diapause as adults (95% CI 26.1 - 62.7; Table 1). The duration of detritivores was strongly tied to regional temperature, with duration being much longer in warm regions compared to cool regions (Figure 5C). In addition to there being a phylogenetic signal in species-specific intercept and the species-specific slope of temperature, variation in duration was also partially explained by the phylogenetic signal in the species-specific precipitation slope (Supporting Information Figure 2). The partial R2 of our best duration model was 0.75 (Supporting Information Figure 3). The number of observations used to estimate the phenometrics was included as a predictor variable in the top duration model, as well as in the top emergence and termination model.