Thermal death kinetics of fifth-instar Plodia Interpunctella (Lepidoptera: Pyralidae)

Authors: Johnson, Judy; WANG, S - WASHINGTON UNIVERSITY; TANG, J - WASHINGTON UNIVERSITY

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/6/2002
Publication Date: 4/1/2003
Citation: Johnson, J.A., Wang, S., Tang, J. 2003. Thermal death kinetics of fifth-instar Plodia Interpunctella (Lepidoptera: Pyralidae). Journal of Economic Entomology. 96(2):519-524. http://handle.nal.usda.gov/10113/29176.

Interpretive Summary: A major problem in the storage and marketing of dried fruits and nuts in California is infestation by Indianmeal moth, Plodia interpunctella. Currently, the dried fruit and tree nut industry relies on fumigation with methyl bromide and phosphine for postharvest insect control. Although non-chemical treatments for postharvest dried fruits and nuts have been investigated, recent concerns over resistance, regulatory action and the needs of the organic industry have generated a renewed interest in developing alternative treatments. Heat treatments using forced hot air or hot water dips have been proposed for a variety of postharvest insect pests but the lengthy exposure times needed may reduce product throughput or cause product damage. Radio frequency and microwave systems may avoid these problems by providing more rapid product heating. Knowledge of thermal death kinetics for targeted insects such as the Indianmeal moth is essential in developing thermal treatments utilizing microwave or radiofrequency heating. In this study, we used a heating block system developed by Washington State University to determine the thermal death kinetics of fifth instar Indianmeal moth larvae and compare their relative heat tolerance to the previous target species. We obtained 95% mortality at exposures suitable for practical radio frequency treatments (less than or equal to 5 min) with temperatures of 50 and 52°C. Diapausing larvae were significantly more tolerant than non-diapausing larvae at the lowest treatment temperature and shortest exposure, but differences were not significant at more extreme temperature-time combinations. Previous studies showed that fifth instar larvae of the navel orangeworm, Amyelois transitella, were more heat tolerant than either diapausing or non-diapausing Indianmeal moth larvae. Consequently, efficacious treatments for navel orangeworm would also control Indianmeal moth.

Technical Abstract: Heat treatments have been suggested as alternatives to chemical fumigants for control of postharvest insects in dried fruits and nuts. Conventional forced hot air treatments heat product too slowly to be practical, but radio frequency treatments are capable of more rapid product heating. While developing radio frequency heat treatments for dried fruits and nuts, the heat tolerance of non-diapausing and diapausing fifth instar larvae of the Indianmeal moth, Plodia interpunctella, was determined using a heating block system developed by Washington State University. Both a 0.5th order kinetic model and a classical empirical model were used to estimate lethal exposure times for temperatures of 44-52°C for non-diapausing fifth instar larvae. We obtained 95% mortality at exposures suitable for practical radio frequency treatments (less than or equal to 5 min) with temperatures of 50 and 52°C. Diapausing larvae were significantly more tolerant than non-diapausing larvae at the lowest treatment temperature and shortest exposure, but differences were not significant at more extreme temperature-time combinations. Previous studies showed that fifth instar larvae of the navel orangeworm, Amyelois transitella, were more heat tolerant than either diapausing or non-diapausing Indianmeal moth larvae. Consequently, efficacious treatments for navel orangeworm would also control Indianmeal moth.