Effect of Relative Humidity and Product Moisture on Response of Diapausing and Nondiapausing Indianmeal Moth (Lepidoptera: Pyralidae) Larvae to Low Pressure Treatments

Abstract

Low pressure treatment in flexible polyvinyl chloride containers is a potential alternative to chemical fumigants for California tree nuts. Laboratory studies investigated the effect of relative humidity and product moisture on weight loss and mortality of diapausing and nondiapausing larvae of the Indianmeal moth, Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae), exposed to 50 mmHg. Diapausing larvae were far more tolerant than nondiapausing larvae to low pressure; exposure times nearly twice those of nondiapausing larvae were required to obtain comparable weight loss or mortality levels in diapausing larvae. Relative humidity was found to have a large effect on both weight loss (assumed to be due to moisture loss) and mortality of both nondiapausing and diapausing larvae. Mortality and weight loss increased as humidity levels decreased. By controlling the relative humidity of the treatment chamber, product moisture also strongly affected weight loss and mortality. The results suggest that for tree nuts, product moisture levels may affect the efficacy of low pressure treatments.