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 chemical 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). Treatment with codling moth granulovirus may be necessary before these thresholds are reached.

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 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.
For Madex Top, a maximum of ten sprays each giving 8-14 days protection is allowed per season (a maximum of six sprays per generation)
Application should be made just before egg hatch is expected to ensure larvae pick up virus particles as they move from the egg to the apple entry point. Application a little bit too early is preferable to a little bit too late.
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 sunny 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 ten sprays per annum.
The virus is compatible with most fungicides. Higher volume sprays are considered to be more effective as they offer improved crop coverage. 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, so the granulovirus can also be considered as a multiple season population management tool.
Users 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.
Using granulovirus products to target the second generation close to harvest also risks superficial ‘sting’ damage which affects the grade-out of the apples where high populations of the pest are experienced.

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 Explicit) or spinosad(Tracer)
Several insecticides including deltamethrin, chlorantraniliprole (Coragen), indoxacarb (Steward or Explicit) 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 the insect growth regulator pyriproxyfen (Harpun)
Pyriproxyfen (Harpun) is an insect growth regulator (IGR) that mimics juvenile hormone. Juvenile hormone is a necessary chemical produced during an insect’s development, but becomes toxic when present during metamorphosis.

Pyriproxyfen is ‘bio-residual’ providing pest control several weeks after application.
Pyriproxyfen inhibits egg hatch, inhibits metamorphosis of nymphs to adults and reduces the fecundity of adult females (eggs laid are sterile).
The strategy is to target eggs or early larval stages to suppress the population.
There is no immediate lethal effect but effect can be seen during mating or with larval degradation during hatching.
Adsorption of the product is best when freshly laid eggs are treated up to 24 hours after laying.
Adsorption is reduced with egg ageing.

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 RAK 3+4 mating disruption system

RAK 3+4 is a combined pheromone control system which reduces fruit damage from codling moth (RAK 3) and summer fruit tortrix (RAK 4). Both pheromones disrupt mating behaviour and therefore prevent populations from developing. The pheromones are released from sealed chambers by volatilisation, preventing male and female moths from locating each other and reproducing.

RAK 3+4 is most effective in orchards with a low pest population density. It should not be used in orchards where more than 1% of fruits (including fallen fruits) were damaged by codling and tortrix moths in the preceding year, unless the first generation of moths is treated with a control product to reduce initial populations.
Best results are achieved in isolated orchards, i.e. those which are 100 m or more away from other orchards or high trees.
Optimum results are also achieved in grouped orchards containing trees of similar size and shape.
RAK 3+4 will not be effective if there is a high density of codling moth and/or tortrix moth in the area adjacent to the orchard being treated. It will not be effective in orchards less than 1 ha in area.

Timing of application and dose rate

The pest population should be monitored using an appropriate pest forecasting system or monitoring traps and the product should be put in place one week before the forecast arrival of the adult moths.
The latest time of application is when the first generation of adult moths start to fly. Only one application of product per season is required.
The product is packaged in airtight bags and protected from the light. The package should therefore only be opened immediately prior to installation to avoid any loss of efficacy.
RAK 3+4 should be used at a rate of 500 product units per ha. The density should be increased at the orachrd border – see below.

Positioning the dispensers

The pheromone must be distributed evenly throughout the orchard in a grid system at 500 product units per hectare. One should be placed approximately every 20 square metres, e.g. for a row width of 3.5 m a unit should be placed every 5.7 m.
It is important to make sure that they are positioned in the shade or in places which will be in the shade by the end of vegeative growth.
The product must be placed in the upper third of the trees, preferably at alternating heights.
The manufacturer provides further guidance on using additional pheromone around the orchard borders to prevent moths from encroaching into the treated orchard from adjacent areas.
Further guidance is provided on the use of additional pheromone monitoring traps to check on the efficacy of the pheromone on a weekly basis.

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.