Codling moth, Cydia pomonella, is a quarantined pest of pome fruits, stone fruits, and walnuts.  It presents a major barrier in the development of export market for these products (Tebbet et al. 1986) to apple growing countries like Japan and the Republic of Korea in which this insect pest does not occur.  These countries have strict quarantine regulation prohibiting the importation of fresh host fruits from any country where the insect occurs (Moffitt and Burbitt, 1989).  Generally a postharvest quarantine treatment of fruit is required, which can guarantee that no life stages of the Codling moth are present in shipments of fruit.

In some markets, inspection and certification that the insect is not present in the shipment of fruit is sufficient to meet import quarantine requirements. For other markets, chemical fumigation may be required after harvest. Because of phytotoxicity and health and safety concerns, alternatives to fumigation  also have been investigated. Exposure to low temperatures and oxygen, such as those commonly used for storage of apple and pears, is also a possible alternative to fumigation treatment for codling moth eggs and larvae.

The objective of this paper is to review all work done on postharvest quarantine control of the Codling moth. However, a little is known on this aspect of postharvest technology. The presence of the Codling moth in produce, can seriously disrupt trade among countries. Thus, an effective Codling moth treatment, which is not harmful to the commodity, workers, or the consumers, is essential for allowing unrestricted movement of fresh pome and stone fruits, and walnut in domestic (among states within U. S.) and international commerce. There is a dire need to develop an effective and safe integrated quarantine management program for postharvest control of the Codling moth on pome and stone fruit, and walnut.
 
 

Several disinfestation procedures employing chemical, physical, or irradiation treatments, have been developed to eliminate insects from produce. Of these treatments three are in commercial use and are accepted by the quarantine authorities of various importing nations. They are fumigation with gaseous sterilants, storage at low temperatures, and a short exposure to high temperature. Very few countries have approved ionizing radiation as a disinfestation treatment for fruit.
 

Fumigation

Fumigation with gaseous sterilants is the most important technique for disinfesting produce. Methyl bromide (MB) is the most widely used fumigant for horticultural produces (Bond l984). Effective fumigation was provided in the past by ethylene dibromide (EDB), carbon disulphide, and hydrogen cyanide. Carbon disulphide and hydrogen cyanide are flammable and highly toxic to humans (Wills et al. 1989). Use of EDB as a fumigant on produce for consumption in the U.S. was prohibited from September l, 1984, because of its suspected carcinogenicity (Wills et al. 1989). MB is currently under attack based upon some recent reports of carcinogenicity on laboratory animals. Withdrawal of MB registration is seriously under consideration in the United States.  Therefore, alternative treatments must be developed if agriculture and the food supply are to be protected (Mitchell and Kader 1985).
 

A low concentration, or shorter duration of fumigation, combined with cold treatment is considered less injurious to the commodity than fumigation alone. MB is applied to produce either in a permanent fumigation chamber or in a temporary enclosure, such as gas-tight rail car and road truck. The permanent chamber offers the safest and most reliable fumigation.
 

Heat Treatment

Proceduce can be successfully disinfested by exposure to high temperature, a process known as vapor-heat treatment. This treatment is effective for fruits like mango, papaya, and pineapple. It requires a prolonged exposure (more than 8 hours plus heating time) to moist heat at temperatures as higher as 112 °F (44.4 °C). This has been sufficiently injurious to fruits like pome and stone fruits. It has been suggested, however, that a short treatment time may make heat treatment specially appealing.
 

Cold Treatment

Many insects that infest produce do not tolerate exposure to low temperatures, an observation that has led to an effective disinfestation procedure for deciduous fruits but not for tropical and sub-tropical fruits, which are liable to chilling injury. The 1976 U.S. quarantine manual allows cold treatment for fresh commodities from areas infested with the Mediterranean fruit fly.  There are strict requirements for temperature monitoring in cold storage facilities in order to certify compliance with the required cold treatments.
 

Microbial Control

Bacillus thuringiensis has been used against stored grain pests. There is a possibility of using Codling moth granulosis virus combined with other methods for the control of newly hatched Codling moth neonates on apple and pear destined for the export market.
 

High Carbon Dioxide and Low Oxygen Levels

Some storage insects are controlled by exposure for 4-8 days to under 0.5 % oxygen, or above 80% carbon dioxide. Stored dried products should tolerate such conditions and may even show beneficial effects in terms of slower deterioration rates. Recent studies suggest that such treatments of bulk almonds may be more economical than the conventional MB fumigation. Studies are needed to evaluate the potential for effective control of major quarantine insects under such atmospheres, alone and in combination.
 

Ultrasound and Microwave

Use of these techniques shows preliminary indications of insect control, but much more study is needed to verify the effectiveness and to evaluate product tolerance and commercial acceptability.

Radiation

The egg phase of the life cycle of an insect is the most sensitive to radiation, followed by larvae, pupae, and adult stages. Most insects are sterilized at doses of 0.05 to 0.2 kilogray; some adult moths will survive 1 kilogray, but their progeny are sterile (Wills et al., 1989). Very few countries have approved ionizing radiation disinfestation treatment for fruit, and no fruit is yet being so treated commercially (Wills et al., 1989). This may change with the introduction of restriction on disinfection by chemicals.
 
 

In 1971, Moffitt demonstrated that Codling moth larvae on harvested apples could be killed without phytotoxic effects by fumigating apples with low doses of methyl bromide, 32 g/m3 for 24 hours, and then placing them for thirty days in standard cold storage. Moffitt (1971) quoted unpublished data by H. Roth, which indicates that fumigation at low levels of MB will not always provide 100% mortality of Codling moth larvae. Unfortunately, levels above 32 g/m3 may injure the fruit (Monro, 1969). Morgan et al (1974 ) found that rate of 32 g/m3 of MB for 2 hours did not injure red delicious, golden delicious, spartan, jonathan, or newtown apples. They found that fumigation alone, without subsequent cold storage, could kill all stages of Codling moth, whereas standard cold storage all first and second and some third, instar larvae in non-fumigated fruit.

Fumigation with MB effectively controlled certain stages of Codling moth infesting apples (Moffitt 1971, Morgan et al. 1974) and cherries ( Anthon et al. 1977, Gaunce et al. 1981) at normal atmospheric pressure (NAD), and in walnuts fumigated at reduced pressure (VAC) of 100mm Hg ( Nelson and Hertsell 1983). Tebbets (1986) found that nondiapausing fifth instars fumigated at 20 or 30 °C and NAD and diapausing larvae fumigated at 20 °C and VAC were less tolerant of MB: diapausing larvae were 2-3 fold more tolerant of MB than nondiapausing larvae. Lethal doses decreased at higher temperatures. However, fumigation at a reduced pressure of 100 mm Hg significantly increased toxicity of MB. When reduced-pressure fumigated, the response of diapausing larvae was not significantly different compared with nondiapausing larvae fumigated at normal atmospheric pressure. Gaunce et al. (1980), found that 1 day old Codling moth eggs were the least susceptible to MB, and were difficult to kill at 32 g/m3 MB for 2 hours at 21 °C.

Comparison of the studies mentioned above indicated that the stages of the Codling moth from least to most tolerant of MB are as follows: adult < nondiapausing larvae in cocoons < eggs (particularly those early in development) < diapausing larvae in cocoons (disturbed) < pupae (particularly those early in development) < diapausing larvae (undisturbed) in cocoon < 1 day old egg.

Yokoyama et al. (1987) developed a MB quarantine treatment for disinfesting nectarines of CM for export to Japan. They tested efficacy of MB on artificial infestation of 24 hour old CM eggs on nectarine cultivars such as May Grand, Firebrite, Red Diamond, Spring Red, Summer Grand, and Fantasy. They proposed a fumigation of 48 g/m3 for 2 hours at 21°C or above for potential use as a quarantine treatment to disinfest nectarines from CM. Their results demonstrated that early to mid-season packed nectarines treated with MB fumigation would be CM-free. This conclusion is further supported by the quarantine treatment of 32 g/m3 MB for 2 hours at 21°C for CM in exported apples (Moffitt 1971, Morgan et al. 1974, Gaunce et al. 1988) and cherries (Anthon et al. 1975, 1977, Gaunce et al. 1981) which recommended 16 g/m3 less MB than the dosage found efficacious for CM on nectarine.

Acceptance of the quarantine treatment of 48 g/m3 MB for 2 hours at 21°C or above and a load of 50% (Yokoyama et al. 1987) by U S and Japanese regulatory agencies allowed the first shipment of California nectarines to enter Japan in 1988 (Yokoyama et al. 1990). Currently, regulatory agencies require that the quarantine treatment be tested against 1 day old Codling moth eggs (Yokoyama et al. 1990), the stage least susceptible to MB (Gaunce et al. 1980), on each nectarine cultivar before consideration for export (Yokoyama et al. 1990). Yokoyama et al. 1990 evaluated the Codling moth egg chorion and fruit thickness to determine if interactions between the insect and fruit might result in a difference in insect susceptibility to MB. They measured fruit cuticle thickness in areas without Codling moth eggs and beneath Codling moth eggs on nectarine, peach, plum, and apple cultivars. They observed that the cuticle was slightly thicker on all fruit in areas beneath Codling moth eggs. A significant difference in cuticle thickness in areas with and without Codling moth eggs was only observed in peaches. The difference in cuticle thickness in peaches could have resulted from reduced desiccation in areas beneath eggs. Their measurements of cuticle thickness were similar to those reported by Miller (1983) for nectarine and apple. They concluded, based on these results, that the susceptibility of Codling moth eggs to MB would not be affected by the fruit cuticle. They also found that Codling moth eggs were significantly less
 
 

susceptible on peaches. The minimum tested doses to cause 100% mortality of Codling moth eggs on nectarine, peach, and apple cultivars and wax paper are shown in the Table 1. These doses are well below the 48 g / m3 MB used in the quarantine treatment for nectarine cultivars. Yokoyama et al. (1990) found no evidence that Codling moth ovipositional behavior, egg fruit interactions, Codling moth response to MB in dose response and confirmatory tests, or Codling moth on different substrates will affect efficacy of the quarantine treatment.

Gaunce et al. (1981) reported that fumigation with MB provided complete control of Codling moth eggs on cherries at a mean temperature of 22.2 to 24°C. Their results indicated a substantial effect of temperature on the susceptibility of eggs. They found that fumigation with 32 g/m3 of MB for 2 hours with fruit temperatures at 19.5 °C and above with a chamber load of 49% could obtain a complete kill of larvae of Codling moth in sweet cherries. These findings supported the findings of Anthon et al. (1975) on efficacy of MB fumigation to kill Codling moth larvae in cherries.
 
 

Because of phytotoxicity and health and safety concerns, alternatives to chemical fumigants are desirable (Moffitt & Burditt 1989). Exposure to low temperature, such as those commonly used for storage of apple and pear, is a possible alternative to fumigation of moth eggs and larvae. Moffitt and Albano (1972) determined the effect of standard-cold (SC) and controlled- atmosphere (CA) storage on the various stages and ages of CM (Table 2). They found that diapausing larvae was the only stage of Codling moth that survived the 133 days in storage.
 
 

Table 2 shows the differential effects of type and length of storage on diapausing larvae. Total mortality was greater in CA storage, but complete mortality never occurred. Mortality in storage after 30 and 133 days was greater than in the unstored control. They found that exposure to either type of storage altered the sex ratio of the adults developing from the surviving diapausing larvae: more females than males survived all exposure, particularly in CA storage. They also found that adults from surviving diapausing larvae had greater longevity, more ovipositing females, more females depositing fertile eggs, and a higher percent egg hatch than adults from surviving pupae. This means that storage (either SC or CA) of as much as 133 days was not sufficient to kill all stages of the CM. Therefore, such periods and such conditions of storage could not guarantee that stored fruit will be completely free of all live stages of the CM.

Morgan (1974) found that standard cold storage killed all first and second and some third instar larvae in nonfumigated fruit. However, Codling moth were more tolerant of fumigation with MB than are nondiapausing larvae (Gaunce et al. 1980, Tebbets et al. 1986), but they were more sensitive to low temperature. Newcomer (1930) reported that exposure of eggs on apple to temperatures ranging from -1.1 to 0.6°C resulted in 99.2% mortality. Moffitt and Albano (1972) reported complete mortality of 24-72 hour and 72-120 hour old eggs from about 30 day exposure to approximately 0.6°C.Yokoyama and Miller (1989) reported complete mortality of (0-24 hour old) eggs from about 15-21 days exposure to 0°C. Results of studies by Moffitt and Burditt (1989) showed that about 42 day exposure at a temperature near 0°C would be required for complete mortality of Codling moth eggs on apples. This suggests that exposure to low temperatures shows promising potential as a treatment after harvest and as an alternative to fumigation for Codling moth eggs on host fruit.
 
 

Gaunce et al. (1982) found Codling moth to be sensitive to a high concentration of carbon dioxide. In general, Codling moth is more susceptible to the carbon dioxide than to the oxygen deficient atmosphere. The order of increasing tolerance to the 60% CO2 atmospheres was adult, egg, larva, pupa, and diapausing larva. The low oxygen atmosphere produced similar effects. Gaunce et al. (1982) reported 99% mortality with a 2 day exposure to 95% carbon dioxide at 27°C in contrast to results of Soderstrom and Brandl (1989), which show the same mortality with 10-12 day exposure to 60% carbon dioxide at 25 °C. Soderstrom and Brandl (1989) found that adult mortality was essentially unaffected with atmospheres below 40% Carbon dioxide. They found that egg deposition was reduced at 40% and 60% carbon dioxide, and was affected also by length of exposure.

The potential for low oxygen and / or elevated carbon dioxide appears quite promising particularly against the egg stage. This quarantine procedure needs to be explored further on fruits like apple, pear, and walnut. However, it is probably not feasible for fresh stone fruits because of their short storage life and because these controlled atmospheres readily reduce fruit quality (Soderstrom and Brandl 1989).
 
 

The objective of combination treatments is to reduce the concentration of MB for the quarantine treatment of Codling moth. Exposure to low temperatures for periods as short as 55 days is not enough to cause complete mortality of Codling moth larvae, therefore, other treatments such as fumigation with MB will be necessary for a complete quarantine control of Codling moth. Morgan et al. (1974), concluded that fumigation with methyl bromide at 32 g/m3 for 2 hours followed by standard cold storage at -0.5°C for 31 to 35 days would kill all Codling moth larvae without injuring the apples. Exposure to low temperatures shows promising potential as a postharvest quarantine treatment for Codling moth eggs. As the Codling moth egg is more tolerant to MB than is the larva (Gaunce et al. 1980, Tebbets et al. 1986), control of eggs with cold treatment will allow less rigorous regimes of fumigant to be used against larvae. Use of less rigorous regimes will substantially reduce the risk of unacceptable phytotoxic effects on fruit from fumigation with MB (Drake et al. 1988). Since Codling moth eggs are sensitive to a high concentration of carbon dioxide, there is another possibility to modify atmosphere (oxygen and carbon dioxide levels) in the storage for their control, in combination with either fumigation by MB at low doses to control susceptible larvae or low temperature such as below 2°C to control all stages of the Codling moth. There is a possibility that application and proper monitoring of the cold treatment/modified atmosphere may be achieved during marine transport.
 
 

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