Synergistic effects of heat and diatomaceous earth treatment for the control of Plodia interpunctella (Lepidoptera: Pyralidae)

Plodia interpunctella is a major economic pest that commonly infests most stored and processed agricultural products. Currently, heating at 50-60°C for at least 48 hours is applied in facilities for disinfestation. However, this condition requires a great deal of time and expenses. To improve the control efficiency of this system, we conducted combined treatments with heating and diatomaceous earth (DE), which is known to be toxic to pest insects. DE effect was compared between 25°C or 40°C to wandering fifth instar larvae, which is the mostly tolerant stage to heat. When larvae were brushed with DE powder, mortality was only 15.0-18.3% at 25°C for 10 days, but rapidly increased to 100% at 40°C within 4 h post-treatment. In addition, when larvae were kept in the plastic cage with DE [4 mg/L (w/v)], their mortality was 100% in 24 h at 40°C post-treatment, otherwise mortality was only 8.8% without DE. Thus, the control efficiency of heating significantly improved with the combination of DE. These effects increased further at higher temperatures and with longer exposure time. Our results clearly showed that DE treatment showed synergistic effects on heating systems for the control of P. interpunctella.