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Abstract How have recent changes in temperature means and variability altered selection on and evolution of the thermal sensitivity of insect growth? We address this question for cabbage white butterflies, Pieris rapae , by repeating a 1999 study that linked lab measurements of the temperature sensitivity of short-term growth rates to fitness components (survival, development time, final body size, and fecundity) in the field. In 1999, selection favored increased growth at low temperatures at the expense of decreased growth at high temperatures. We document evolution consistent with this past selection: caterpillars now grow faster at low temperatures but slower at warm temperatures in 2024 compared to 1999. However, temperatures have changed rapidly, with increasing incidence of high temperatures such that selection in 2024 has reversed to favor increased growth at the highest temperature assayed. Over the 25 years, phenotypic variation has increased at warm temperatures and a tradeoff between growth at intermediate and warm temperatures has strengthened, consistent with evolutionary constraints that may restrict evolution to grow faster at rare, high temperatures. Our study demonstrates the potential for rapid evolution of thermal sensitivity in response to climate change in an agricultural pest. However, selection to initially capitalize on warming temperatures can ultimately decrease fitness as warming temperatures move into a stressful range, driving reversals in the direction of selection.