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In apple and pear, the larvae often enter through the calyx (eye) or the ripening cheek of maturing fruits, although entry may occur anywhere on the fruit surface. They then bore down to the core of the fruit, leaving a prominent entry hole which has a red coloration around its rim. This hole becomes blocked with brown excreta (frass) as the larvae continue to feed on the flesh and seeds of the fruit. A smaller, unblocked exit hole can be seen on the fruit later, once the larva has escaped. Attacked fruit also tends to drop prematurely, often during the 'June drop'. A single larva will usually attack only one fruit, and fruits are seldom attacked by more than one larva. Damage is generally greater in areas where there are two generations or more per year.
Orchard areas adjacent to apple bins, pallet and box stores or unsprayed apple trees are particularly prone to attack, and removal of these or ensuring adequate spatial separation is an important means of cultural control. Infested fruit should not be dumped in or near orchards. Older fruit trees with rough bark favour codling moth because they provide numerous pupation sites. Where possible, loose bark should be removed. Stakes and tree ties should have as few crevices as possible. Loose bands of corrugated cardboard, sacking or other suitable materials, about 100 mm wide, may be placed around tree trunks before pupation to provide artificial pupation sites. These may be temporarily removed and the larvae or pupae beneath destroyed. These latter measures are likely to be practicable only on a small scale.
The use of biological control against codling moth has been reviewed by Madsen and Morgan (1970), Leroux (1971) and Falcon and Huber (1991), and a more recent review of biological control of apple and pear pests is being published by Cross et al. (1999). Although research has produced useful insights into the biological control of codling moth by exploitation of existing populations of natural enemies such as birds, spiders, insects, nematodes, bacteria, fungi and protozoa, none has been shown to give adequate control.
The identification, mass production, testing and commercial exploitation of Cydia pomonella granulosis virus (CpGV), important events in the annals of insect pathology and biological control, have been reviewed by Falcon and Huber (1991). CpGV was first discovered in Mexico in 1963 (Tanada, 1964) and its use for biological control is now well established. Its commercial development and use was limited at first for a number of reasons: high costs relative to pesticides (the virus has to be cultured in its host); slow action allows neonate larvae to cause superficial 'sting' damage to fruitlets before death; short persistence due to sensitivity to UV light; and selectivity relative to pesticides. However, the development of strains of codling moth resistant to insecticides, lower cost mass-production techniques, and the desire to reduce dependence on broad-spectrum insecticides, have led to increasing commercial use of CpGV in recent years.
The efficacy of CpGV in numerous field experiments has ranged from 70% to over 90% control, somewhat lower than for the best insecticides where codling moth populations have not developed resistance to insecticides (Cravedi and Molinari, 1983; Dickler, 1983; Glen and Payne, 1983, 1984; Richards et al., 1983; Charmillot et al., 1984; Glen et al., 1984; Dickler and Huber, 1986a; Geoffrion, 1986; Blommers et al., 1987; Jaques et al., 1987). However, considerable additional winter mortality is caused by the virus. The use of CpGV in combination with insecticides or with pheromone mating disruption (Charmillot, 1995; Trematerra et al., 1996) would probably be the most appropriate strategy for exploiting the virus in an IPM programme.
Insect growth regulators (IGRs) such as diflubenzuron, which interfere with the normal formation of the cuticle and deposition of chitin, have given acceptable control of codling moth in field tests on apples and pears in many fruit-growing regions (Wearing and Thomas, 1978; Westigard, 1979; Riedl and Hoying, 1980; Burts, 1983; Charmillot and Iselin, 1985). However, as diflubenzuron acts primarily as an ovicide on the codling moth, spray coverage is very critical for good control. Other IGRs such as epofenonane (superseded) and fenoxycarb act by contact or ingestion and can have an ovicidal effect, interfere with moulting, and inhibit metamorphosis to the adult stage.
Different apple varieties have been shown to vary in their susceptibility to codling moth (Painter, 1951), Jonathan being one of the more resistant cultivars. Putman (1963) suggested this was due to the epicuticular wax being toxic to neonate larvae. The walnut variety Franquette also shows a high level of resistance to codling moth, but needs further investigation.
The components of the sex pheromone emitted by females to attract males have been identified, (E,E)-8,10-dodecadien-1-ol (EEOH) being the active ingredient (Roelofs et al., 1971). Since its discovery, pheromone traps have been used to monitor adult male activity. They give a good indication of the likely level of attack in an orchard and are most useful for optimizing the timing of sprays.
The pheromone mating disruption (confusion) technique is an effective control method for codling moth, becoming a reality in 1991 with the registration of a product by Pacific Biocontrol. Numerous vials containing the pheromone are placed at intervals throughout the orchard before the flight begins. The technique is most effective where large areas of orchard are treated. Initial populations of C. pomonella have to be low, or the technique has to be combined with another control strategy (e.g. granulovirus or insecticides) for successful control. Control using this technique is more costly than conventional insecticides, and therefore is used mainly in areas where the C. pomonella has developed resistance to insecticides, e.g. the South Tyrol, Italy and Washington State, USA. In western USA, the level of codling moth control in mating-disrupted blocks was shown to be as good as in blocks using conventional control methods (Brunner et al., 1998). Establishment of the USDA-ARS-funded Codling Moth Area-wide Management Project (CAMP) in 1994 has increased grower awareness in the USA and, as a result, in Washington State alone the use of codling moth mating disruption has increased from 600 ha in 1991 to an estimated 10,500 ha in 1997. This mating disruption will no doubt become a very important control strategy against C. pomonella in the near future as the use of organophosphates becomes more restricted.
Another effective strategy exploiting the sex pheromone is 'lure and kill'. One effective method under development in Switzerland (Charmillot et al., 1996, 1997a, b) uses mastic paste impregnated with a mixture of the pheromone and a synthetic pyrethroid insecticide (permethrin). Small quantities are extruded from a mastic gun at intervals onto the trees throughout the orchard. Male moths are lured to the baits and become contaminated with insecticidally treated mastic which kills them within a few hours.
IPM programmes involving biological control with granulovirus (CpGV) have been devised and implemented throughout Europe during the past 20 years (Falcon and Huber, 1991). Classical biological control methods have not succeeded (Clausen, 1978; Geier, 1981) and the sterile insect technique has only limited success in Canada (Proverbs et al., 1977; Dyck and Gardiner, 1992).
Due to the variable regulations around (de-)registration of pesticides, we are for the moment not including any specific chemical control recommendations. For further information, we recommend you visit the following resources:
Crop losses caused by codling moth on pome fruits around the world are difficult to assess, as the methods used are often inadequate and not strictly comparable. According to Vickers and Rothschild (1991), commercial orchards using broad-spectrum insecticides correctly can keep codling moth damage to below 2%. In Nova Scotia, the degree of infestation under insecticide-free conditions varied from 6 to 10% of the entire crop in an orchard over 12 years, depending on the cultivar (MacLellan, 1977). In an orchard in Lake Ontario, USA, where there is one generation and a partial second, similar to those seen in southern England, damage ranged from 7 to 35% (Glass and Lienk, 1971). In warmer climates, where two or more generations occur, damage to apples has been reported as being as high as 84% in the Crimea (Tanskii and Bulgak, 1981), or 65 to 100% in Australia (Geier, 1964).