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Codling moth – additional information

Life cycle

Codling moth has one complete and one partial generation per year in southern Britain, though two generations occur in hot summers.

  • The first, stronger generation, occurs between mid May and late July.
  • The second generation occurs between August and October, and though damaging to the crop, does not contribute to the following year’s population.
  • Adults fly at and after dusk on warm evenings at temperatures >15 degrees C.
  • Eggs are laid singly on foliage of fruitlets. They hatch 10-14 days depending on temperature. Egg development takes 85.5 +/- 8.9 degree days above a threshold of 10 degrees C.
  • Larvae invade fruit (see ‘Damage’) and pass through 5 instars becoming fully grown in about 4 weeks.
  • Larvae vacate fruit and spin cocoons under loose bark, in cracks in the trunk or supporting stake etc. or in dead plant material in the ground cover.
  • Most larvae over-winter in their cocoon and pupate in Spring, but those that spin by the end of July may pupate and produce a second, usually partial, generation of adults in August and early September.
  • Late-developing larvae still inside the fruits after harvest often form their cocoons in cracks in apple bins or other places in fruit stores and pack-houses.

Pest status

Key pest of apple, less frequently pear though attacks on pear can be very damaging. Attacks fruit directly, so economically important at low population densities.

Other hosts

Walnuts,  Malus sp, quince.

Varietal susceptibility

Host plant resistance is not known to occur in apple cultivars though some Malus sp. with high malic acid content may be resistant.

  • Early harvested varieties may escape attack from second generation larvae.
  • Pear varieties with stone cells round calyx (e.g. Bartlet) are of low susceptibility as larvae are unable to penetrate flesh.

Distribution

Widespread and common. World-wide distribution wherever apples are grown except possibly Japan and parts of S.America.

Damage

Newly hatched larva (one per fruit) burrow through skin into the flesh and through to the core.

  • The entry point is often at the calyx (smaller fruits) or on the cheek (larger fruits).
  • The entry hole is prominent and red-ringed, characteristically blocked by dry frass.
  • Cut open fruit to reveal cavity, frass and sometimes the larva.
  • Damaged fruits often fall prematurely and are found on the ground under the tree.

Other pests with which codling moth may be confused

Fruitlet mining tortrix
Larval attacks by the fruitlet mining tortrix occur shortly after blossom.

Blastobasis decolorella
Caterpillars sometimes burrow into fruits from July-September, but damage is usually associated with extensive surface damage.

Recognition

Adult (resting)
Length 8-11 mm, ash grey with characteristic coppery blotch at wing tip.

Egg
1.3 x 1.0 mm, flat, oval and translucent. Found on foliage or fruits, mainly the latter when fruits are more mature.

Larva
Typical tortrix form with 5 pairs of prolegs, none on the first two abdominal segments. Up to 20 mm long, pale pinkish white (younger instars whitish). Head and pro-thoracic plate brown. Usually found inside fruit.

Pupa
Inside thin cocoon. 8-10 mm long, brown. Often found in bark and other crevices.

Other pests with which codling moth may be confused

Apple sawfly
Sawfly larvae are also found in fruit but only up to mid-June. Sawfly larvae taper to tip of abdomen and have 7 or more pairs of pro-legs, though the first abdominal segment is without prolegs.

Fruitlet mining tortrix
Larval attacks by the fruitlet mining tortrix occur shortly after blossom.

Blastobasis decolorella
Caterpillars sometimes burrow into fruits from July-September, but damage is usually associated with extensive surface damage. Blastobasis caterpillars are dark purple-brown in colour.

Monitoring

Pheromone traps
The flight activity of male moths should be monitored using sex pheromone traps. The delta trap design is used widely.

  • Traps should be set out in orchards shortly after blossom (where the fruitlet mining tortrix is a problem locally, codling moth traps, which also attract males of the fruitlet mining tortrix, should be set out before blossom).
  • Ideally, each orchard should be individually monitored with at least one trap.
  • The traps should be hung from the branch of the tree at canopy height in the centre of the orchard and oriented to allow air flow through the trap by the prevailing wind.
  • The number of moths caught in each trap should be recorded weekly and the dead moths removed.
  • Lures should be changed every 4-6 weeks as recommended by the manufacturer. A 4 week interval is better in hot weather. Sticky bases should be changed when their effectiveness declines significantly.
  • The usual threshold for treatment is a single catch of 5 or more moths per trap per week from May to July (first generation, fruit less susceptible) and 3 per trap per week from August to September (second generation, fruit more susceptible).

Egg counts
AHDB Horticulture funded research (Project TF 189) showed that pheromone trap catches don’t give a good indication of when the pest is actually laying eggs in apple orchards. Instead, regular egg counting on fruitlets is probably the only fully reliable and accurate way of determining whether and when an orchard needs spraying, but it’s time consuming and unlikely to be done by growers or their consultants.

An alternative way of predicting when egg laying has occurred is to use the RIMpro-Cydia forecasting model in conjunction with sex pheromone monitoring traps (see below).

Fruit damage
Inspecting fruits for damage either whilst developing on the tree or at harvest or grading, may indicate if populations are high and damage is likely from the next generation.

  • Dropped fruits on the ground under the tree may also be examined in summer.
  • Damage exceeding 1% of fruits infested is cause for concern.

Trunk banding
Applying trunk bands may be used for monitoring.

  • Set a band of currugated cardboard covered with cling film on a sample of trees and count the number of cocooning larvae and pupae.

Forecasting egg laying using the RIMpro-Cydia model

AHDB Horticulture  funded Project TF 204 assessed the effectiveness of the computer based life-stage simulation model RIMpro-Cydia at forecasting egg laying.

  • The RIMpro-Cydia model was found to be a useful indicator of egg-laying risk but needs calibrating.
  • A threshold ‘risk factor’ of 100 tends to overestimate the risk of egg laying and larval emergence which, if the model is used alone to time control sprays, can result in applying more sprays than may be necessary.
  • It’s also difficult to set the parameters of the model to produce a reasonable prediction of the risks from second generation egg laying.
  • Use of the RIMpro-Cydia model in conjunction with pheromone trap records – only spraying if the forecast indicates a risk of egg laying and the pheromone trap threshold is exceeded – will help avoid unnecessary early sprays when males are flying and there is little or no risk of egg laying.
  • The results of the project suggest that the interval between sprays should be shortened where crop damage from codling moth was significant in the previous year or when weather is hot, and highlights the importance of continuing to monitor and treat for the pest in August and September.

Biological control

Codling moth granulovirus
Now that the codling moth granulovirus (Cyd-X) is available and approved for use in the UK, it should be used wherever possible, bearing in mind the following limitations:

  • It only controls codling moth and not tortrix moths, Blastobasis or other pests
  • A maximum of three sprays each giving 8-14 days protection is allowed per season
  • Heavy attacks may result in some superficial sting injury as the young larvae hatching from eggs do not die immediately.

Key aspects of the virus are:

  • The virus is highly selective and virulent. In orchards, only codling moth can be infected. A single virus particle is sufficient to kill a first instar codling moth larva. The virus is totally safe to man, plants and the environment, though the formulants included in the product may be harmful. No ‘pesticide residues’ occur on fruits at harvest.
  • The virus has to be ingested by the newly hatched larva when feeding on the skin of the apple before it penetrates the flesh. The larva continues feeding for a few days before the virus acts. This results in small, shallow, larval feeding holes in the surface of the fruit, known as ‘sting’ injury. Although sting injury is superficial, it can result in downgrading of fruit to a lower quality class. This injury is the main disadvantage of the virus.
  • The virus is sensitive to UV light and high temperatures which limit its persistence. In hot/sunny weather, protection lasts about 8 days. In cooler, cloudy weather protection lasts up to 14 days.
  • A programme of sprays of the virus at 8-14 day intervals, starting from the onset of egg hatch (see ‘Chemical control’) and continuing until hatch is complete is usually required, remembering that there is a maximum of three sprays per annum.
  • The virus is compatible with most fungicides. Higher volume sprays are considered to be more effective. A feeding stimulant, such as molasses, sugar or milk powder may be added to the spray solution to increase the amount and rate of larval feeding and hence improve the efficacy of the treatment.
  • First generation larvae that overwinter can carry over sub-lethal infections of the virus to the following season
  • User of the granulovirus against the second generation of codling moth in late July or August as opposed to using insecticides will reduce the likelihood of pesticide residues occurring on fruits at harvest. However, in the UK, the second generation larvae do not usually complete their development, so mature larvae and pupae carrying sub-lethal infection will not be carried over to the next season.

Bacteria
Sprays of Bacillus thuringiensis (Bt) at the egg-hatch period may give a limited degree of control of codling moth.  However, the newly hatched larvae only feed for a short time before boring into the fruit and do not usually ingest an adequate dose.

Nematodes
A spray of the entomopathogenic nematode Steinernema carpocapse applied to the trunk and main branches in September or early October can give over 80% control of cocooning larvae.

  • However, it is vitally important that the weather conditions are suitable at the time of application and after application.
  • The air temperature must be above 14 °C and the surface of bark must remain wet for at least 24 hours during and after application..
  • The spray should be applied at high volume. Nematodes are exempt from pesticide registration requirements, but they must be a native strain or a strain licensed for release in the UK.

Parasitic wasps
Egg parasites (Trichogramma sp.) are available from biological suppliers and can be introduced but efficacy is poor even if huge numbers are introduced making the method uneconomic.

Chemical control

Although codling moth resistance to insecticides  is widespread in other countries, it has probably not yet developed in the UK.  Chemical control therefore remains the principal means of control in the UK because it is both cheap and effective.

Control with larvicides including pyrethroids, chlorantraniliprole (Coragen), indoxacarb (Steward) or spinosad(Tracer)
Several insecticides including cypermethrin, deltamethrin, chlorantraniliprole (Coragen), indoxacarb (Steward) and spinosad (Tracer) are approved for control of codling moth or other caterpillars on apple in the UK and act by killing larvae.

  • For codling moth control, the newly hatched larvae must be exposed to a lethal dose before they burrow into the fruit, either by ingestion or contact action.
  • The use of synthetic pyrethroids should be avoided as they are harmful to predatory mites and other natural enemies.
  • Note also that pyrethroids are broad-spectrum compounds which are harmful or toxic to humans and the environment.
  • The first spray for each generation is timed to coincide with the onset of egg hatch. This time is determined from pheromone trap catches.
  • The first above-threshold catch (single catch of 5 or more moths per trap per week from May to July) indicates the date when egg laying commences.
  • Eggs take on average 7-10 days to hatch, but the length of time varies greatly with temperature.
  • The first spray is applied 7-10 days later (use the shorter interval in warm weather) to coincide with the onset of egg hatch.
  • The duration of egg development can be calculated more accurately if desired from daily maximum and minimum air temperatures.
  • Cumulate the percentage egg development that occurs each day starting from the first day that an above threshold pheromone trap catch is obtained.
  • The day can usually be determined within a day or two by looking at daily temperatures and identifying particularly warm days in the week preceding the weekly record of the catch.
  • Moth flight generally occurs when dusk temperatures are >15 deg C. However, accurate calculation of the date of hatching is not very important as most insecticides are fairly persistent and give control for 2-3 weeks providing they are applied before significant egg hatch has started.
  • The first spray against the first generation neonate caterpillars will generally be 5-6 weeks after petal fall in the second half of June, but may be earlier if the weather is warm.
  • An effective residue of insecticide needs to be maintained on the leaf and fruit surface throughout the duration of the egg hatch period.
  • A single spray is normally sufficient where infestations are light but two or more sprays may be necessary for more severe infestations as indicated by continuing high pheromone trap catches.
  • The interval between sprays depends on the effective persistence of the product used. In hot summers there may be a second generation in August which can be very damaging.
  • This may justify a further spray but care must be taken to avoid infringing harvest intervals, especially on early varieties.

Control with chitin synthesis inhibitor insecticide diflubenzuron (Dimilin)
Chitin synthesis inhibitor insecticides inhibit the development of chitin, which is the protein from which the insect’s skin (exoskeleton) is formed.

Diflubenzuron (Dimilin) is a chitin synthesis inhibitor with ovicidal and larvicidal activity against codling moth.

  • It is a selective insecticide which is comparatively safe to humans and the environment and very effective against codling moth.
  • However, it can have adverse effects on earwig populations thereby causing outbreaks of other pests for which earwigs are important natural enemies, notably woolly aphid.
  • It is reputed to be particularly harmful to earwigs if sprayed at night as earwigs are nocturnal.
  • The first spray of diflubenzuron (Dimilin) for codling moth control is applied at the onset of egg-laying i.e. as soon as the first threshold catch occurs.
  • It is important not to delay spraying for 7-10 days until egg hatch as a deposit of the insecticide has to be present before or shortly after the egg is laid for best results.
  • Further sprays may be necessary if the egg laying period is prolonged or if there is a second generation.
  • The main disadvantage of diflubenzuron (Dimilin) as a codling moth control agent is that it is not effective against the summer fruit tortrix moth, another important pest which may require chemical control at this time.

Control with the juvenile hormone analogue insecticide fenoxycarb (Insegar)
Juvenile hormone is an insect hormone which controls morphogenesis (from larva to pupa) and egg development in insects. Juvenile hormone analogues such as fenoxycarb (Insegar) interfere with these natural processes, causing mortality.

  • Although fenoxycarb (Insegar) is not specifically recommended by the manufacturer for control of codling moth on apple or pear, it is recommended for control of the summer fruit tortrix moth and will give incidental control of codling moth where it is used.
  • It is a juvenile hormone analogue and only acts against codling moth eggs, not against larvae which are inaccessible to the insecticide at the susceptible late-larval stages when they are inside fruits. It has 2-3 weeks effective residual activity on leaves and fruits.

Control with the moulting accelerating insecticide methoxyfenozide (Runner)
Methoxyfenozide (Runner) is a moulting acceleration insecticide and is effective mainly when ingested on the egg to L2 larval stages.

  • It has minimal contact action.
  • The active ingredient mimics the action of the moulting hormone (ecdysone) of moth larvae (L1 – L2 stages), and differs from other insect growth regulators such as the chitin biosynthesis inhibitor diflubenzuron (Dimilin) or juvenile hormone analogue fenoxycarb (Insegar).
  • Upon ingestion, caterpillars undergo an incomplete and developmentally lethal premature moult.
  • After ingestion, larvae cease feeding within 4-8 hours.  They die because they are unable to feed and complete the moulting process.
  • The first spray of methoxyfenozide (Runner) is best applied a few days before the onset of egg hatch of codling moth.
  • It has 2-3 weeks effective residual activity and is very effective against other caterpillar pests of apple including tortrix moths and Blastobasis.
  • Note that a maximum of 3 sprays is permitted per season

Insecticide resistance

Codling moth populations are widely resistant to conventional and insect growth regulator insecticides in southern and central Europe. The resistance has forced growers in those regions to adopt alternative control strategies, mainly using pheromone mating disruption and/or codling moth granulovirus. Resistance has not been shown to occur in the UK.

Avoiding the development of insecticide resistance

Although codling moth has probably not yet developed resistance to insecticides in the UK, resistance is widespread in other countries, especially where the moth has multiple generations.

  • There is a risk that resistant moths will be imported on fruit or nursery trees from these countries but the probability of this happening is low.
  • The chance of the resistance developing in the UK can be greatly reduced by alternating the group of insecticide used for control and not relying on insecticides from one group continually.

Sex pheromone control

There are three basic methods by which a pest’s sex pheromone can be exploited for control:

  • Mating disruption where the pheromone is used alone to interfere with the normal attraction of males to females by providing false trails and/or sensory overload
  • Mass trapping where the sex pheromone is used to attract males to a trap where they are captured and killed physically
  • Attract and kill where the sex pheromone attracts males to a device or place where they come into contact with an insecticide

The Exosex CM codling moth pheromone autoconfusion system
This is a special mating disruption system and is the only sex pheromone control system currently approved and available for control of codling moth in the UK. It provides another codling moth control option.

  • A lattice of 25 delta dispensers per ha is set out in a grid through the orchards at the start of the codling moth flight in May, as indicated by sex pheromone trap catches.
  • Each dispenser contains wax powder loaded with the codling moth sex pheromone in its base and a sex pheromone lure.
  • The lure attracts males into the dispensers where they become contaminated with the pheromone loaded powder which is attracted electrostatically to their bodies.
  • Contaminated males are confused and also attract other males so preventing or delaying mating of females.
  • Like other sex pheromone mating disruption systems, it only gives adequate control of low codling moth populations and should be used in combination with other codling moth control measures including granulovirus and or insecticides.

Other pheromone mating disruption systems
Conventional mating disruption systems utilise a lattice of pheromone dispensers, typically 500-1000 per ha containing up to 150 g of pheromone per ha, spread through the orchard just as adult moths start to emerge.

  • Male moths are confused by the synthetic pheromone and are unable to find females.
  • Although commercial products are available in many other European countries and are used on a large scale, there is currently no approved product for use in the UK.
  • Pheromone mating disruption is most successful if used on a large scale and when populations are low initially.
  • It is generally more expensive than chemical control or biocontrol using the codling moth granulovirus and has a high labour requirement for application.
  • For this reason it is only used in areas where codling moth has developed resistance to insecticide.

Pheromone attract and kill:
The sex pheromone is incorporated into a material together with an insecticide (usually a synthetic pyrethroid).

  • Blobs of the material are extruded onto the trunk and branches of trees throughout the orchard (typically 1-2 blobs per tree) at the start of moth flight, as indicated by pheromone traps.
  • The males attempt to mate with the blobs, picking up a dose of insecticide in the process.
  • The technique is effective and uses a fraction of the amount of insecticide used in an insecticide spray treatment.
  • However, no product is approved for use in the UK currently.

Other non-chemical control methods

Sterile insect release
In Canada, codling moths are mass-reared, sterilised and released in an area-wide codling moth control programme.

  • The sterile males mate with the wild females which lay infertile eggs. Insecticide sprays are not then needed for control.
  • The approach is effective, though costly and cannot be used by individual growers.

Cultural control

Many cultural control approaches require high labour inputs and are only likely to be appropriate where other effective control measures are not available.

Old trees

  • Old trees with rough, creviced bark provide numerous cocooning sites for larvae.
  • Young trees with smooth bark may be less severely attacked.
  • In this situation, many codling moth larvae spin cocoons and hibernate in dead plant material in the ground cover.

Spatial isolation

  • Commercial orchards should be isolated as far as possible from unsprayed orchards and garden trees which are often a source of infestation.

Hygiene

  • Fallen, infested fruits may be removed promptly and destroyed before larvae can exit and move to cocooning sites.
  • Developing fruits may be inspected in July and infested fruits removed and destroyed.
  • Bulk bins may be disinfected after use.
  • Discarded fruit from the pack-house should not be allowed to act as a source of infestation.

Trunk banding

  • A band of sacking, corrugated cardboard or another suitable material may be secured round the trunk of each tree in June before larvae exit the fruitlets.
  • The band will provide a cocooning site for larvae.
  • The band should be temporarily removed in August and cocooning larvae destroyed.
  • This process should be repeated in winter.

Natural enemies

Codling moth has many natural enemies but these are not sufficiently effective to regulate populations below damaging levels.

Insectivorous birds
Tits, especially, pick larvae and pupae in cocoons from bark crevices, but do not forage specifically for the pest unless population densities are very high and for this reason are of only limited value.

Egg parasites
The egg parasite Trichogramma can be introduced (4 releases of 2.5 m per ha have been shown to reduce damage by 50-80%) but such introductions are not cost effective. Ascogaster quadridentatus is a common, naturally-occurring parasite which lays a single egg in the codling moth egg but develops within the host larva.

Larval/pupal parasites
Many species of parasitic wasp attack codling moth larvae and/or pupae.

Predatory insects
Earwigs and predatory mirid and anthocorid bugs are known to feed on Codling moth eggs and young larvae.

Entomopathogenic fungi
Many species of entomopathogenic fungi, notably Beauveria bassiana, cause significant mortality in overwintered larvae and pupae.

Entomopathogenic nematodes
Neoaplectana carpocapsae are significant natural enemies of overwintering larvae/pupae on tree trunks, especially close to the soil surface.

Virus diseases
Codling moth granulovirus is usually associated with biocontrol applications though the virus can overwinter from one year to the next at a low level.

 

Further reading

Van der Geest, L. P. S. & Evenhuis, H. H. (Eds). 1991. Tortricid Pests, Their Biology, Natural Enemies and Control. World Crop Pests, Vol. 5. Elsevier, Amsterdam.