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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, but diflubenzuron (Dimilin) notably has poor efficacy against summer fruit tortrix moth and should not be used.

  • Summer fruit tortrix moth may be controlled with  indoxacarb (Steward), methoxyfenozide (Runner) or 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.
  • 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 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.

Control with the Juvenile Hormone Analogue insecticide fenoxycarb (Insegar):

  • Juvenile hormone is an insect hormone that controls metamorphosis from larva to pupa in some insects. The concentration of the hormone falls to very low levels when caterpillars are mature, signalling metamorphosis to the pupal state.
  • Fenoxycarb (Insegar) is a juvenile hormone analogue which acts on mature caterpillars that are about to pupate. Juvenile hormone also plays a role in egg formation in the adult insect and in egg development after oviposition.
  • However, these modes of action of fenoxycarb (Insegar) are of lesser importance in the summer fruit tortrix moth (though the effects on eggs are important for codling moth against which the chemical is ovicidal).
  • Fenoxycarb (Insegar) is applied against mature (last instar) overwintered summer fruit tortrix moth caterpillars in spring whilst they are feeding on the blossom trusses and before pupation.
  • The aim is to virtually eradicate the pest so that first and second generation numbers are subsequently so low that control is unnecessary.
  • The timing of spray application is critical. If application is too early, most of the caterpillars will be in the fourth instar stage of development, which is less susceptible to the insecticide.
  • If the application is too late, a significant proportion of the caterpillars will have pupated and these will not be affected. The critical last instar development stage often coincides with the blossom time of Cox apples.
  • Fenoxycarb (Insegar) has a high risk to bees and must not be applied during bloom. The insecticide does not appear to affect adults directly but affects the brood.
  • On apple, a spray of fenoxycarb (Insegar) should be applied just before bloom at the ‘pink balloon’ growth stage.
  • If high populations of the pest are present (as indicated by pheromone trap catches or damage the previous year or by the presence of significant numbers of summer fruit tortrix moth caterpillars at the green cluster growth stage), a second application should be made at 80% petal fall or later.
  • This second application will also give 2-3 weeks ovicidal protection against codling moth. It is important to check bees are not foraging.
  • The success of the treatment should be evaluated by monitoring populations of the pest subsequently with pheromone traps.
  • Regular use of fenoxycarb will suppress populations to very low levels.
  • A moderate pheromone trap catch does not indicate that treatment has been unsuccessful.
  • Female moths that develop from caterpillars that have fed on low doses of fenoxycarb are often sterile.

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 8oC 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 10oC 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 10oC after 1 January.

Forecasting the timing of egg hatch

  • Egg development takes approximately 103 day-degrees C above a threshold temperature of 8.6oC.
  • 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.

Further reading

Charmillot, P. –J. & Brunner, J. F. 1989. Summerfruit Tortrix, Adoxophyes orana: Life cycle, warning system and control. Entomologia Hellenica 7, 17-26.

Cross, J. V. 1997. The susceptibility of summer fruit tortrix moth, Adoxophyes orana (Lepidoptera: Tortricidae), to chlorpyrifos and strategies for insecticidal control in orchards. Annals of Applied Biology 131, 197-212.

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.