Author
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Johnson, Judy |
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Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 2/9/2010 Publication Date: 6/1/2010 Citation: Johnson, J.A. 2010. Effect of Relative Humidity and Product Moisture on Efficacy of Low Pressure Treatments Against Indianmeal Moth. Journal of Economic Entomology. 103(3):612-618. Interpretive Summary: A major problem in the storage and marketing of California tree nuts is infestation by a variety of postharvest insect pests. Currently, tree nut processors depend on chemical fumigants to disinfest large volumes of incoming product after harvest and to control infestations during storage. Recent concerns over pest resistance, regulatory actions and the needs of the organic industry have generated a renewed interest in developing non-chemical alternative treatments to fumigants. One possible non-chemical alternative is the use of low pressures (vacuum) to disinfest product. Laboratory studies investigated the effect of relative humidity and product moisture on weight loss and mortality of diapausing and non-diapausing larvae of the Indianmeal moth exposed to low pressures (50 mm Hg). Diapausing larvae were far more tolerant than non-diapausing larvae to low pressure; exposures nearly twice those of non-diapausing 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 non-diapausing 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. For both larval stages, complete mortality occurred at about 50% moisture loss. The results suggest that for tree nuts, product moisture levels may affect the efficacy of low pressure treatments. This research will be used to develop treatment recommendations for this practical, effective and environmentally friendly disinfestation method, allowing processors to market insect-free product without the use of chemical fumigants. Technical Abstract: Low pressure treatment in flexible PVC 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 non-diapausing larvae of the Indianmeal moth, Plodia interpunctella (Hübner) exposed to 50 mm Hg. Diapausing larvae were far more tolerant than non-diapausing larvae to low pressure; exposures nearly twice those of non-diapausing 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 non-diapausing 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. For both larval stages, complete mortality occurred at about 50% moisture loss. The results suggest that for tree nuts, product moisture levels may affect the efficacy of low pressure treatments. |
