Radio Frequency Treatments for Postharvest Codling Moth Control in Fresh Apples

Efficacy of using radio frequency (RF) at 27.12 MHz was evaluated as a postharvest quarantine treatment against fi fth instars of the codling moth [Cydia pomonella (Lepidoptera: Tortricidae)], in apples (Malus sylvestris). Tests under the given conditions demonstrated that the energy fi elds between the RF unit’s electrodes were neither predictable nor uniform. Moving fruit submerged in water during RF exposure may improve uniformity, but pulp temperatures varied considerably among fruit, among sites on the same fruit, and at different depths within the same site. As a result of these inconsistencies, quarantine effi cacy was not obtained either using a range of fi nal average temperatures from 40 to 68 °C (104.0 to 154.4 °F) or at holding times up to 20 minutes. We concluded it would be diffi cult to obtain the appropriate parameters for treatment effi cacy and fruit quality maintenance using this technology under these conditions. Apples exported to Japan must meet quarantine security. The codling moth is a pest of concern [Ministry of Agriculture, Forestry and Fisheries-Japan (MAFF-Japan), 1950]. The currently approved procedure is a combination of cold storage followed by methyl bromide fumigation (Hansen et al., 2000; Moffi tt et al., 1988). However, because methyl bromide has been identifi ed as an agent that depletes ozone by the U.S. Environmental Protection Agency (U.S. Congress, 1990) and the Montreal Protocol (United Nations Environmental Program, 1995), its continued use in quarantine treatments is in question. Methyl bromide currently has an exemption for postharvest quarantine use, but its cost is increasing. Among the alternatives to methyl bromide fumigation (irradiation, controlled atmosphere, cold, other chemicals), heat treatments have generated the most interest. Yokoyama et al. (1991) measured codling moth mortality in the egg and larval stages exposed to 45 to 51 °C (113.0 to 123.8 °F) for different durations. Neven (1994) examined mortality of fi fth instar codling moth after heat treatments of 43 to 45 °C (109.4 to 113.0 °F) followed by cold storage for 0 to 5° C (32.0 to 41.0 °F). Jones and Waddell (1997) directly submerged codling moth eggs and larvae in 43 to 49 °C (109.4 to 120.2 °F) water baths for various durations and determined their survival rates. Thermal death kinetics of codling moth larvae were further evaluated by the use of a unique heating block system (Tang et al., 2000; Wang et al., 2002a, 2002b). An innovative method of heating is to use radio frequency (RF) energy, which has longer wavelengths than microwaves. This is done by dielectric heating generated from internal resistance to very rapid alterations of polarity (Headlee and Jobbins, 1936). Three radio frequencies have been allocated by the U.S. Federal Communications Commission for industrial use: 13.56 ± 0.067, 27.12 ± 0.160, and 40.68 ± 0.020 MHz (Wang et al., 2001). This technology seems attractive for postharvest application in that heating is fast and linear with time, energy can penetrate deep into the commodity, there are no chemical residues, and the process has minimal impact on the environment (Tang et al., 2000). RF treatments show promise in controlling stored product pests of walnuts (Juglans regia) (Wang et al., 2001, 2002b). A saline water immersion with RF exposure may be more feasible for fruit (Ikediala et al., 2002). Because RF has not been used as a postharvest treatment to control codling moth in apples, our objectives were to determine the temperature uniformity in water loads and to examine the utility of such technology for postharvest quarantine control.