In warmer environments, most ectotherms reach maturity at a smaller body size (the temperature-size rule, TSR). However, in such environments, growth is usually accelerated and would be expected to result in maturation at a larger body size, leading to increases in fecundity, survival, and mating success, compared to maturation at a smaller size (the ‘life-history puzzle’). To explore mechanisms, we reared Aldrichina grahami at 20 ℃, 25 ℃ and 30 ℃, and added a nutritional challenge by using dilutions of pork liver paste to provide diets that ranged in quality from high (undiluted, control) to moderate (1/8), low (1/16) and poor (1/24). Larvae were randomly sampled for weighing from hatching. Growth curves were fitted to the relationships between growth rate and weight for the third instar larvae. Our results showed that body size was affected by an interaction between temperature and diet, and that TSR and TSR exceptions (E-TSR) could be interconverted by underfeeding. Moreover, when the TSR was followed as temperature increased, there was a cross-over point divided the two growth curves into early and later stages, which could be used to help understand the life-history puzzle in warmer temperatures, with the instantaneous growth rate being higher in the early stages of development and then lower in later stages. This study reminds us that animals evolved to cope with multiple simultaneous environmental changes, and offered a better understanding for life-history puzzles.