Differential induction of heat shock protein genes to the combined treatments of heat with diatomaceous earth, phosphine or carbon dioxide on Plodia interpunctella

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 day1 after heat treatment at 40°C for 6h; however, mortality rates increased after combined treatments of heat and 1ppm DE or 10ppm PH₃, while 10% CO₂ had no significant effect. Quantitative real-time PCR analysis showed that combined treatments involving 1h 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, 1h 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.