Life cycle

There is one main generation per annum in the UK with a partial second generation in late August and September. The second generation is more marked in hot years which favour rapid development of the first generation.

• Larval development has seven instar stages.
• The pest overwinters mainly as a third, sometimes second, instar larva in a silken hibernaculum beneath a bud scale, between a dead leaf and a twig or spur or in crevices in the bark or other shelter.
• After emergence in spring, shortly after bud-burst, individual larvae feed in or amongst the buds, often tying them and rosette leaves together with webbing.
• Fifth instar larvae feed on developing fruitlets, making cavities in the receptacle, which later heal to form corky scars characteristic of early caterpillar feeding.
• Sixth and seventh instar larvae tend to live on foliage.
• Larvae pupate when fully fed, normally in late May or early June.
• First generation adult moths emerge three weeks later, normally in late June and early July, and often a week or two after the flight of codling moth has exceeded the threshold.
• Eggs are laid in batches on the foliage. These hatch in 2-3 weeks depending on temperature (see ‘Forecasting’ below).
• Cool and wet weather conditions at the time of moth flight and/or during egg-hatch limit population increase.
• The tiny first instar larvae spin webs of silk, usually on the undersides of leaves close to the veins leaves, often at a junction between the main and a side vein, and begin to feed.
• They feed on leaves, often between two spun leaves or where two or more fruits are touching or in the calyx cavities of fruits.
• A greater proportion of third instar larvae feed on fruits. Most larvae overwinter in this third instar stage.
• A proportion of more advanced larvae complete their development in August and a partial second generation of adults occurs in August and September.
• These hatch in September or early October and the young larvae feed on leaves overwintering if they reach the second or third instar development stage.

Pest status

Moderately important pest of apple and pear. Attacks foliage and fruit.

Other hosts

Highly polyphagous, the larvae feed on a wide range of trees and shrubs including fruit trees and bushes.

Varietal susceptibility

All varieties are susceptible but those with fruits that are short stalked and/or which hang in clusters, tend to suffer the most damage.

Distribution

Common and widely distributed. One of the most abundant species associated with fruit trees.

Recognition

Adult(resting)
Length 9-12 mm, forewings purplish ochreous with distinctive dark reddish brown markings.

Egg
Flat, almost circular, light green. Black centre when mature. Laid in scale-like batches on leaves.

Larvae
Up to 22 mm long. Yellow-green, olive green or dark green, usually with a black head, though head colour is not diagnostic. Last body segment breathing pores (spiracle) larger than rest. Spins fine webbing and often occurs in leaf rolls or beneath a leaf tied to fruit.

Other pests with which fruit tree 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 summer fruit tortrix moth, Adoxophyes orana, occur commonly in orchards in the UK, especially in the south and east, and are particularly difficult to distinguish from those of the fruit tree tortrix moth.

Damage

• Larvae are leaf-rollers but damage to foliage is unimportant.
• Damage to fruits occurs at different times during fruit development:
• Overwintered larval feeding cavities in the receptacle of flowers and young fruitlets later heal to form corky scars characteristic of early caterpillar feeding on mature fruits.
• Young caterpillars make small, shallow holes in the skin of fruits in July and August.
• Larger caterpillars graze shallow irregular patches in the skin, especially at the point where fruits are in contact.

Monitoring

Pheromone traps
The flight activity of male moths (along with that of the codling moth and summer fruit tortrix moth) should be monitored using sex pheromone traps (a different trap is used for each species). 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. Sticky bases should be changed if their effectiveness declines.
• The economic threshold is considered to be 30 moths per trap per week, though this may be a conservative estimate.
• Temperature sums to predict egg hatch to determine correct timing of egg hatch sprays should be started from the date when the first threshold catch is recorded.

Fruit damage inspection
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.

Forecasting

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

Control methods

Chemical control

Control with indoxacarb (Steward or Explicit), spinosad (Tracer) or the synthetic pyrethroid deltamethrin (Decis Forte etc):

Indoxacarb (Steward or Explicit), spinosad (Tracer) and the synthetic pyrethroid insecticide deltamethrin (Decis Forte etc) are approved for control of tortrix moth and other caterpillars in apple orchards in the UK.

• Synthetic pyrethroid insecticides, which are very effective against the pest, should be avoided because they are harmful to predatory mites and other natural enemies.
• Chlorantraniliprole (Coragen) is thought to offer incidental control when applied against codling moth.
• First generation caterpillars may be controlled by a spray of one of these insecticides timed to coincide with the onset of egg hatch.
• The first threshold pheromone trap catch (30 moths/week) indicates the date when egg laying commences.
• The first insecticide spray should be applied about 2 weeks later.
• These insecticides will also control codling moth which flies slightly earlier than fruit tree tortrix moth and sprays of these insecticides applied for codling moth usually also give good control of fruit tree tortrix moth.

Control with the insect growth regulator pyriproxyfen (Harpun):
Pyriproxyfen 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 larva 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.
• It should be noted that pyriproxyfen (Harpun) is new to the UK in 2020. It is recommended for use against codling moth so it is assumed that it may offer incidental control against fruit tree tortrix moth, but only experience of using it will confirm this.

Control with Bacillus thuringiensis:
See ‘Biological control’ below.

Insecticide resistance

Resistance of fruit tree tortrix to insecticides is not known to occur.

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 reduced losses.
• Furnishing the trees with artificial refuges for earwigs and other insect predators (see rosy apple aphid) is likely to help reduce young caterpillar populations.

Natural enemies

The fruit tree tortrix moth has many natural enemies. Parasitic wasps reduce populations to comparatively low levels in unsprayed orchards but parasites are less abundant in orchards sprayed with broad-spectrum insecticides.

Insectivorous birds
Tits especially pick overwintering larvae from bark, 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
Parasitic wasps (Trichogramma sp.) attack the eggs but parasitism rates are generally low.

Larval and pupal parasites
Several parasitic wasps and flies parasitise fruit tree tortrix moth larvae or pupae.

• Common species are Meteorus ictericus which develops inside the host larva before exiting the larva at the third instar stage, spinning a cocoon nearby. The host larva is not devoured entirely and remains alive for a period of time, eventually dying without further development.
• Apanteles ater is another common internal larval parasite.

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

Virus diseases
No virus diseases of fruit tree tortrix moth have been reported.

Biological control

A programme of weekly sprays of Bacillus thuringiensis (Bt) (Dipel DF) throughout the egg hatch period gives fairly good control but is costly compared to other insecticides.

• 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.
• Bt is not detected by conventional pesticide residue analysis.

Biotechnological control

Mating disruption systems for tortrix moths in apple orchards are used in other European countries and are effective against fruit tree tortrix moth providing initial populations are low.

Further reading

Hey, G. L. & Massee, A. M. 1934. Tortrix investigations in 1933. Annual report for East Malling Research Station 1933, 228-230.

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.