Heating is one of the many disinfestation methods commonly used in facilities that store and process agricultural products. In this study, we have investigated whether the combination of heat treatment with diatomaceous earth (DE), phosphine (PH3) or CO2 affects the mortality of the wandering larvae of Plodia interpunctella, which is a major pest found in most stored agricultural products. The mortality rate was 35.0% at day 1 after heat treatment at 40°C for 6 h; however, mortality rates increased after combined treatments of heat and 1 ppm DE or 10 ppm PH3, while 10% CO2 had no significant effect. Quantitative real‐time PCR analysis showed that combined treatments involving 1 h of heat treatment with either DE, PH3 or CO2 increased the mRNA levels of four heat shock protein (hsp) genes (hsp25, hsp70, grp78 and hsp90) in wandering larvae, 1 h post‐treatment, although those rates were slightly differentiated in each heat shock protein. Our results demonstrate that combinations of heat and DE or PH3 show increased lethality, although insects produce stress responses at the molecular level.