Summer fruit tortrix moth – additional information

Life cycle

There are two generations per annum in the UK.
Larval development has five instar stages.
The pest overwinters as a second or third instar larva in a silken hibernaculum in crevices in the bark etc.
There is often considerable winter mortality which is sometimes an important limiting factor in population development.
After emergence in spring shortly after bud-burst, individual larvae feed amongst the buds, characteristically tying them and the rosette leaves together with webbing.
On early apple varieties and on pears, larval feeding produces cavities in the receptacle, which later heal to form corky scars characteristic of early caterpillar feeding.
Larvae pupate when fully fed, normally around blossom time of Cox.
First generation adult moths emerge in June.
Eggs are laid in batches on the foliage. These hatch in 7-10 days depending on temperature (see ‘Forecasting’.
Cool and wet weather conditions at the time of moth flight and/or during egg-hatch limit population increase.
Many larvae migrate to the growing points in shoots where they form leaf rolls.
In July and August more mature larvae feed on fruits before pupation in August.
A second generation of adults occurs in August and September, depositing eggs on leaves and also directly onto fruits.
These hatch and the young larvae feed beneath silken webs spun on the under-surfaces of leaves, often at a junction between the main and a side vein.
In late September and October, larvae have reached the second or third instar stage and migrate to crevices in the bark to overwinter.

Pest status

The summer fruit tortrix moth is an important secondary pest of apple and pear. It attacks foliage and fruit.
Natural enemies reduce populations in the unsprayed situation.

Other hosts

Recorded from over 70 species of plant, mainly from the family Rosaceae, including many hedgerow and woodland trees and shrubs.

Varietal susceptibility

Apple varieties with fruits that are short stalked and/or which hang in clusters, tend to be most susceptible.
Bramley and Discovery are highly susceptible.

Distribution

Not a native of Britain. First recorded at Teynham in Kent in 1950, for many years it was confined to the South East, especially Kent and Essex.

More recently it has spread across much of southern and central England where it is now widespread and common.
It is reputed to be absent from the West Midlands.

Damage

Damage to foliage is unimportant. Damage to fruits occurs at three different times during fruit development:

Overwintered larvae

Feeding cavities in the receptacle of flowers and young fruitlets later heal to form corky scars characteristic of early caterpillar feeding on mature fruits.

First generation larvae

Young caterpillars make small, shallow holes in the skin of fruits in July and early August.
Larger caterpillars graze shallow irregular patches in the skin, especially at the point where fruits are in contact.

Second generation larvae

Damage is similar to that caused by first generation larvae but occurs in late August and September and appears more freshly formed and may be in progress at harvest.

Recognition

Adult (resting)
Length 8-11 mm, light brown with darker brown markings.

Egg
Flat, oval, light green. Black centre when mature. Laid in scale-like batches on leaves and, for the second generation, sometimes on fruits.

Larvae
Up to 18-20 mm long. Yellow-green, olive green or dark green, usually with a brown head, though head colour is not diagnostic. Spins fine webbing and often occurs in leaf rolls or beneath a leaf tied to fruit.

Other pests with which summer fruit tortrix moth may be confused

Larvae of several leaf-rolling tortrix moths are very similar and are difficult to distinguish from each other.

Larvae of the fruit tree tortrix moth, Archips podana, occur commonly in orchards in the UK and are particularly difficult to distinguish from those of the summer fruit tortrix moth.

Monitoring

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

Traps should be set out in orchards shortly after blossom.
Each orchard should be individually monitored with a trap.
The traps should be hung from the branch of a tree at mid canopy height in the centre of the orchard and oriented to allow flow through of the prevailing wind.
The number of moths should be recorded weekly, and captured moths removed.
Lures should be changed every 4-6 weeks as recommended by the manufacturer.
It is important to change them before the second generation.
Sticky bases should be changed if their effectiveness declines.
The threshold for determining whether the pest is a problem in an orchard is 30 moths per trap per week.
However, temperature sums to predict egg hatch to determine correct timing of egg hatch sprays should be started from the date when the catch exceeds 5 moths per trap (see ‘Forecasting’ ).

Shoot damage

During the first half of July, leaves tied by spinning larvae are easily recognisable on the top of the shoots.
If shoot damage exceeds 5-8%, a curative treatment should be applied immediately or postponed to the beginning of egg-hatch of the second generation.

Fruit damage

Inspecting fruits for damage, either whilst developing on the tree, at harvest or during grading (remembering that badly damaged fruit may have been discarded at harvest), indicates if populations have been high and whether treatment is likely to be required for the next generation or the next season.

Trunk banding

Trunk bands can be set on a sample number of trees in early September and the number of overwintering larvae counted during the dormant period.

Chemical control

Various insecticides that are approved for control of colding moth, totrix moths or for general caterpillar control are likely to control summer fruit tortrix moth.

Summer fruit tortrix moth may be controlled with indoxacarb (Steward or Explicit), spinosad (Tracer), or with the biocontrol agent Bacillus thuringiensis, applied to coincide with egg hatch, usually in June.
Chlorantraniliprole (Coragen) is also thought to offer incidental control when applied against codling moth.
Pyriproxyfen (Harpun) may also offer incidental control of summer fruit tortrix moth when applied for codling moth control. It inhbits egg hatch, metamorphosis of nymphs to adtuls and reduces the fecundity of adult females. However, as a new product to the UK in 2020, further experience is required to inform growers and agronomists of its efficacy at controlling summer fruit tortrix moth.
Bacillus thuringiensis is considered to be of only moderate efficacy.
The summer fruit tortrix ganulovirus (Capex) is another option. Highly specific to summer fruit tortrix, it is ideal for use in organic and IPM production systems and has no harvest interval or buffer zone requirement. See information on viruses in biological control section below.
The first spray should be applied at the onset of egg hatch of the first generation. Further sprays should be applied at 7-10 day intervals until the egg hatch period has ended.
Synthetic pyrethroids are highly effective but their use should be avoided as they are harmful to predatory mites and other beneficial insects.
A pre-blossom spray of indoxacarb (Steward or Explicit) or methoxyfenozide (Runner), often applied to control early season caterpillars, will reduce populations of overwintered summer fruit tortrix moth caterpillars, but is unlikely to be sufficiently effective to prevent damaging first and second generations developing subsequently.
The onset of egg laying is taken as the date when the pheromone trap catch exceeds 5 moths/trap/week.
If traps are only examined weekly, the date when this occurred can often be pin-pointed more accurately by examination of daily temperature records.
The moths fly when dusk temperatures exceed 15 °C.
The onset of the egg hatching period occurs 7-21 days later, depending on temperature. It can be calculated accurately from daily maximum and minimum air temperatures using the look-up table (see ‘Forecasting’ ).
The daily percentage egg development amounts are summed from the date of the onset of egg laying. When the sum reaches 90%, egg hatch is imminent and the first spray should be applied.
A second generation occurs in August and September which can be damaging on later harvested varieties. The second generation may be controlled in the same way.

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.

Insecticide resistance

Strains of summer fruit tortrix moth, that are less susceptible to conventional insecticides than strains that occur in unsprayed orchards, have been shown to occur in the UK. However, the reduction in susceptibility is small.

Forecasting

The rate of development of each of the developmental stages of summer fruit tortrix moth is only completed when a specific heat sum has accumulated. The specific heat sums are known and can be calculated each day from the daily maximum and minimum air temperature. The forecasting model PESTMAN can be used to give approximate predictions of the timing of occurrence of each of the life stages of the pest.

Forecasting the time that overwintered caterpillars reach the last instar stage (for timing Insegar sprays)

Overwintered larvae reach the last instar development stage approximately 75‑100 day-degrees C above a threshold temperature of 8^oC starting from 1 January.

Forecasting the start and peak of first generation adults

The start and peak of the flight of first generation adult moths occurs approximately 170 and 210 day-degrees C above a threshold temperature of 10^oC after 1 January.

Forecasting the start and peak of second generation adults

The start and peak of the flight of second generation adult moths occurs approximately 616 and 693 day-degrees C above a threshold temperature of 10^oC after 1 January.

Forecasting the timing of egg hatch

Egg development takes approximately 103 day-degrees C above a threshold temperature of 8.6^oC.
The percentage egg development that accrues at various daily maximum and minimum air temperatures is given in the look-up table.
Sum the daily percentage egg development amounts starting from the day the first pheromone trap catch of 5 or more moths occurred.
Apply the first egg hatch spray when the temperature sum reaches 90-100%.
If above threshold catches continue for more than one further week, a second spray may be necessary 7-10 days later.

Cultural control

Trees which have a dense canopy and vigorous shoot growth tend to support greater populations of caterpillars. If shoot growth then ceases when caterpillars are young, due to water stress and/or a heavy fruit load, the caterpillars tend to move to feed on fruits, especially those in clusters, and damage intensifies.

Avoiding this situation by tree management reduces losses.
The cultural control approaches recommended for codling moth are likely also to be effective in controlling summer fruit tortrix moth, though hygiene measures need to be modified to suit this particular species.
Furnishing the trees with artificial refuges for earwigs and other insect predators is likely to help reduce young caterpillar populations.
Ideally, a refuge should be provided in each tree. This may simply be some extra lengths of hollow tree tie round the stake.
In orchards with high tree densities, it is likely to be impractical to provide more elaborate refuges such as half of a plastic drinks bottle containing a roll of corrugated cardboard.

Natural enemies

Insectivorous birds

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

Egg parasites

The egg parasitic wasp Trichogramma can be introduced (4 releases of 2.5 m per ha have been shown to reduce damage by 40-85%) but such introductions are not cost effective.

Larval parasites

The parasitic wasp Colpoclypeus florus is an external parasite of third to fifth instar summer fruit tortrix moth larvae.
The parasite can be seen attached behind the head of its host.

Predatory insects

Earwigs and predatory mirid and anthocorid bugs feed of eggs and young larvae.

Virus diseases

A nucleopolyhedrovirus (AoNPV) and two strains of a granulovirus (AoGV) of summer fruit tortrix moth are known (see ‘Biological control’ below).
These are normally found in association with commercial applications of biocontrol agents, though natural infections of AoGV were found in two orchards near Faversham in Kent in 1993.

Biological control

Bacillis thurigiensis

A programme of weekly sprays of Bacillus thuringiensis (Bt) throughout the egg hatch period gives fairly good control, though control may not be as good as that achieved with conventional or Insect Growth Regulator insecticides (see below).
Bt has to be ingested to act and is most effective in warm weather when caterpillars are feeding actively.
The bacterium produces a crystalline toxin. The insect dies from the effects of this toxin rather than from pathogenesis due to the bacterium.
Bt is of short persistence as it is degraded by heat and UV light.
It is most effective against newly hatched larvae before they form leaf rolls in which they feed internally and are inaccessible to sprays.
The first spray should be applied at the onset of egg hatch which should be determined from pheromone trap catches and egg development sums calculated from the daily maximum and minimum air temperature (see ‘Forecasting’ ).
Bt is not detected by conventional pesticide residue analysis.

Viruses

Three baculoviruses of summer fruit tortrix moth have been tested for use in the field in Europe including a nucleopolyhedrovirus (AoNPV) and a granulovirus (AoGV).
AoNPV can control summer fruit tortrix very effectively and is highly host-specific but the virus is uneconomic to produce and is not available commercially.
AoGV has a very slow pathogenesis. Newly hatched larvae become infected in the first instar development stage and only die when they reach the final development stage.
They can live longer than uninfected larvae and larval damage to fruit may not decrease in the short term.
In the longer term, a high degree of control can be obtained. The virus may persist for several generations.
A commercial formulation is produced in Switzerland but is not registered for use in the UK.

Biotechnological control

Pheromone mating disruption

Pheromone mating disruption systems have been developed for summer fruit tortrix moth in continental Europe.
One system uses red spaghetti double tube plastic dispensers, one tube containing the pheromone, the other a metal wire to give rigidity.
The dispensers are wrapped round the branch of a tree.
A typical application rate is 1000 dispensers per ha, one application being required per season.
The system was developed to control summer fruit tortrix moth and other tortrix moths, such as Pandemis heparana and Archips rosana, and uses a common pheromone component (Z11-14:Ac).
Pheromone mating disruption systems have a number of important limitations.
They are only effective if populations of the target pest are low initially; they have to be applied over a large area; they are generally costly in comparison with insecticides and they have a high labour requirement for application.
There are no pheromone mating disruption systems approved for use in the UK.

Apple Best Practice Guide