Thermal performance under constant temperatures can accurately predict insect development times across naturally variable microclimates

External conditions can drive biological rates in ectotherms by directly
influencing body temperatures. While estimating the temperature dependence
of performance-traits such as growth and development rate is feasible
under controlled laboratory settings, predictions in nature are difficult.
One major challenge lies in translating performance under constant
conditions to fluctuating environments. Using the butterfly Pieris napi as
model system, we show that development rate, an important fitness trait,
can be accurately predicted in the field using models parameterized under
constant laboratory temperatures. Additionally, using a factorial design,
we show that accurate predictions can be made across microhabitats, but
critically hinge on adequate consideration of nonlinearity in reaction
norms, spatial heterogeneity in microclimate, and temporal variation in
temperature. Our empirical results are also supported by a comparison of
published and simulated data. Conclusively, our combined results suggest
that, discounting direct effects of temperature, insect development rates
are generally unaffected by thermal fluctuations.