Taiwan is the third largest importer of U.S. fresh apples (Taipei Times, 2005). The apples are primarily from Washington and California (Fruit Growers News, 2002), with ‘Fuji’ as the predominant cultivar comprising 80% of those from Washington (Jimenez, 2004). After over 25 years of apple exports to Taiwan, live codling moth larvae were found for the first time in 2002, leading to a temporary ban on U.S. apples (Fruit Growers News, 2002). To resume exports, the United States agreed to increase the numbers of apples inspected and, if live codling moth larvae were found in three consignments, all apple imports from the United States would stop (Taipei Times, 2005).
The systems approach (SA) is being expanded to meet these increasingly severe phytosanitary regulations for apples. The SA involves the cumulative effect of commercial operations to reduce the risk of possible pest infestation followed with validation by intense inspection. One area that can be exploited is the cold storage component. Cold storage is already used against the apple maggot [Rhagoletis pomonella (Diptera: Tephritidae)] (Hallman, 2004) and the oriental fruit moth [Cydia molesta (Lepidoptera: Tortricidae)] (Hansen, 2002) for apples exported to Mexico. A better understanding of the impact of cold storage on codling moth larvae would strengthen this component and improve the overall use of the SA.
Cold storage (55 d at 2.2 °C) for control of codling moth eggs is a component of the current quarantine treatment against codling moth for apples exported to Japan (Hansen et al., 2000). Thus, 1.1 °C, the temperature ‘Fuji’ apples are frequently stored, may also be effective against codling moth larvae. Toba and Moffitt (1991) reported no survivors among 142,000 codling moth larvae after 13 weeks at 1.5% to 2.0% oxygen (O2) and less than 1% carbon dioxide (CO2) and held at 0 °C. However, they based the efficacy of their study on the lack of adult emergence rather than larval mortality.
Furthermore, the insecticidal effect of cold storage may vary as a result of the physiological condition of the codling moth larvae at the time of harvest when they are undergoing preconditioning for diapause, an inactive state that allows the larvae to overwinter within their cocoons (Newcomer and Whitcomb, 1924). Diapausing larvae do not feed and are freeze-tolerant (Brown, 1991). Cold exposures may be less effective against diapausing-destined larvae, but no studies have been done to determine the effect of commercial cold storage, if any. Thus, baseline information for all three physiological stages is necessary to understand the cold storage component.
The objectives of the present study were to measure larval mortality for cumulative durations of regular air (RA) at 1.1 °C, the temperature used for cold storage of ‘Fuji’ apples, the major export cultivar. Feeding larvae of both diapaused-destined and nondiapausing were examined separately. Mathematic models were developed to describe the mortality rates at cold temperature exposures and durations for complete control were calculated.
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