Typically, the relationship between insect development and temperature is described by two characteristics: the minimum temperature needed for development to occur (Tmin) and the number of day degrees required (DDR) for the completion of development. We investigated these characteristics in three English populations of Thrips major and T. tabaci [Cawood, Yorkshire (N53°49', W1°7'); Boxworth, Cambridgeshire (N52°15', W0°1'); Silwood Park, Berkshire (N51°24', W0°38')], and two populations of Frankliniella occidentalis (Cawood; Silwood Park). While there were no significant differences among populations in either Tmin (mean for T. major = 7.0°C; T. tabaci = 5.9°C; F. occidentalis = 6.7°C) or DDR (mean for T. major = 229.9; T. tabaci = 260.8; F. occidentalis = 233.4), there were significant differences in the relationship between temperature and body size, suggesting the presence of geographic variation in this trait. Using published data, in addition to those newly collected, we found a negative relationship between Tmin and DDR for F. occidentalis and T. tabaci, supporting the hypothesis that a trade-off between Tmin and DDR may constrain adaptation to local climatic conditions.