|Hansen, James D|
Submitted to: Postharvest Biology and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/3/2001
Publication Date: 6/28/2002
Citation: WANG, S., TANG, J., JOHNSON, J.A., HANSEN, J.D. THERMAL DEATH KINETICS OF FIFTH-INSTAR NAVEL ORANGEWORM (LEPIDOPTERA: PYRALIDAE LARVAE. POSTHARVEST BIOLOGY AND TECHNOLOGY 38:427-440. Interpretive Summary: A major problem in production, storage and marketing of almonds and walnuts in California is infestation by navel orangeworm, a direct pest of the nutmeats. Postharvest treatments are required to prevent additional product damage by this insect during storage and to ensure clean products before shipment to domestic and international markets. Currently, the dried fruit and tree nut industry relies heavily on fumigation with methyl bromide and phosphine for postharvest insect control. Concerns over resistance and regulatory action have generated a renewed interest in developing alternative treatments to these fumigants. Radiofrequency and microwave heating systems have been suggested for control of postharvest insects, as they provide rapid product treatment. Because heat treatments must be carefully designed to provide adequate insect control while avoiding damage to product quality, detailed information on the response of targeted insects to heat is essential. A heating block system able to directly hea insects and accurately simulate different heating rates from 1 to 20C per minute was developed at Washington State University and used to determine the mortality response of fifth instar navel orangeworm larvae. Complete kill of test insects required a minimum exposure time of 140, 50, 15, 6 and 1 min at 46, 48, 50, 52 and 54C, respectively. The data was used to develop a predictive model that described the mortality response of navel orangeworm to high temperatures. The results suggest that rapid, efficacious heat treatments using radiofrequency or microwave systems could be devised for walnuts and almonds that would not adversely affect product quality.
Technical Abstract: Information on kinetics for thermal mortality of navel orangeworm, Amyelois transitella (Walker) (Lepidoptera: Pyralidae), is needed for developing postharvest phytosanitation thermal treatments of walnuts. Thermal death kinetics for 5th-instar navel orangeworm larvae were determined at temperatures between 46 and 54C at a heating rate of 18C/min using a heating block system. Thermal death curves for 5th-instar navel orangeworm larvae followed a 0.5th order of kinetic reaction. The time required to achieve 100% mortality decreased with temperature in a logarithmic manner. Complete kill of 600 insects required a minimum exposure time of 140, 50, 15, 6 and 1 min at 46, 48, 50, 52 and 54C, respectively. The reaction rate (k) was affected by treatment temperatures following an Arrhenius relationship. The activation energy for thermal kill of 5th-instar navel orangeworm larvae was estimated to be between 510 and 520 kJ/mol.