Development of radio frequency treatments for dried pulses

Authors: Johnson, Judy; WANG, S - Washington State University; JIAO, S - Washington State University; TANG, J - Washington State University

Submitted to: International Conference on Methyl Bromide Alternatives and Emissions Reductions
Publication Type: Proceedings
Publication Acceptance Date: 9/1/2010
Publication Date: 11/1/2010
Citation: Johnson, J.A., Wang, S., Jiao, S., Tang, J. 2010. Development of radio frequency treatments for dried pulses. International Conference on Methyl Bromide Alternatives and Emissions Reductions. November 1-3, 2010, Orlando, Florida. 51:1-3.

Interpretive Summary: Dried pulses are valuable export commodities in the US Pacific Northwest but infestation by insect pests may cause importing countries to require phytosanitary treatments before shipment. Typically, chemical fumigants are used to disinfest product, but the industry is exploring non-chemical alternatives. One possible alternative is the use of radio frequency (RF) energy to rapidly heat product to insecticidal levels. The development of RF treatments requires identification of the most heat tolerant insect stage under RF conditions. The cowpea weevil is a primary pest of concern to countries importing lentils, green peas and chick peas, although laboratory infestation rates in these products are very low. Black-eyed peas and mung beans were identified as better hosts of cowpea weevil, but their response to RF energy must be compared to the target products before their use as surrogate hosts in RF tests. Another issue to be addressed is the possible escape of active cowpea weevil adults as product heats during RF treatments. This paper compares the heating rate of black-eyed peas and mung beans to chickpeas and lentils during RF treatments, determines the relative response of different cowpea weevil stages to RF energy, and examines the behavioral and mortality response of adult cowpea weevil to sudden high temperatures. Data on the dielectric properties and relative heating rates of surrogate legumes (black-eyed peas and mung beans) and their target products (chick peas and lentils) showed that by reducing the moisture content of the surrogate legumes, conservative heating rates could be obtained. This will allow the use of the surrogate legumes in subsequent studies. Relative tolerance of different life stages of the cowpea weevil heated using RF energy suggests young larvae may be most tolerant of the treatment. Although active adults may attempt to escape from elevated temperatures, they enter heat stupor very near the proposed treatment temperature of 60°C. Because the proposed treatment will include forced 60°C air, as adults leave the rapidly heating product they will be directly exposed to these temperatures, and should enter heat stupor rapidly.

Technical Abstract: Chemical fumigants are typically used to disinfest dried pulses of insect pests before shipment to importing countries, but the industry is exploring non-chemical alternatives. One possible alternative is the use of radio frequency (RF) energy to rapidly heat product to insecticidal levels. The cowpea weevil is a primary pest of concern to countries importing lentils, green peas and chick peas, although laboratory infestation rates in these products are very low. Black-eyed peas and mung beans were identified as better hosts of cowpea weevil, but their response to RF energy must be compared to the target products before their use as surrogate hosts in RF tests. Another issue to be addressed is the possible escape of active cowpea weevil adults as product heats during RF treatments. This paper compares the heating rate of black-eyed peas and mung beans to chickpeas and lentils during RF treatments, determines the relative response of different cowpea weevil stages to RF energy, and examines the behavioral and mortality response of adult cowpea weevil to sudden high temperatures. Data on the dielectric properties and relative heating rates of surrogate legumes (black-eyed peas and mung beans) and their target products (chick peas and lentils) showed that by reducing the moisture content of the surrogate legumes, conservative heating rates could be obtained. This will allow the use of the surrogate legumes in subsequent studies. Relative tolerance of different life stages of the cowpea weevil heated using RF energy suggests young larvae may be most tolerant of the treatment. Although active adults may attempt to escape from elevated temperatures, they enter heat stupor very near the proposed treatment temperature of 60°C. Because the proposed treatment will include forced 60°C air, as adults leave the rapidly heating product they will be directly exposed to these temperatures, and should enter heat stupor rapidly.