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Light brown apple moth – additional information

Life cycle

  • There are at least two generations per annum in the UK.
  • Larval development has 5-6 instar stages.
  • Adults can fly between February and Dec, although April to October is more usual.
  • The first generation larvae occur on fruit and leaves in June-July and the second generation larvae over-winter, probably in leaf litter.
  • It is expected that more generations will occur in the UK with climate change.
  • The first generation of moths emerge at the beginning of April from over-wintered larvae and the second generation at the end of July.
  • Eggs are laid in batches on the foliage. These hatch in 2-3 weeks depending on temperature (see ‘Monitoring and Forecasting’).
  • Larvae pupate when fully fed, normally in early May and early June.
  • 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, often at a junction between the main and a side vein, and begin to feed.
  • Later they may feed on the surface of the fruits or in the calyx cavities of fruits.
  • Normally, the rate of larval development is slowed considerably during the winter; thus the majority of larvae over-winter in the prolonged early juvenile phases of the second, third, and fourth instars.
  • During this period they normally feed on herbaceous plants. Re-invasion of apple trees takes place from the beginning of April.

Pest status

Increasing pest of apple and pear and several other fruit crops. 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, will suffer the most damage.

Distribution

Common and widely distributed.

Damage

Larvae are leaf-rollers and damage is similar to other leaf-roller species. Damage to foliage is unimportant. Damage to fruits occurs at different times during fruit development.

  • Early instars often settle on the under surface of leaves close to the main veins, where they construct silken shelters and feed on the leaf tissue sometimes creating small windows in the leaves.
  • Larvae can be found on shoot tips or areas of new growth, where they web the leaves together with silk.
  • A third settlement site is the calyx, where their presence is detected only from observing the fine silken webbing among the sepals.
  • Later larval stages construct feeding niches between adjacent leaves and/or fruit, in the developing bud, or on a single leaf (leaf rolling).
  • Fruit suffers from surface damage, particulary in compact cluster varieties.
  • Internal damage to fruit is less common, but a young larva may enter fruit through the calyx. Excreta are usually ejected on to the outside of the fruit; this does not happen with the codling moth.

Recognition

Adult (resting)

  • In the adults the forewing is characteristically curved.
  • Male moths are 6-10 mm long, with the front part of the forewing generally much lighter than the back, which is rusty dark red/brown.
  • Much lighter forms may also be found.
  • The females are generally larger than the males (7-13 mm long) and are more difficult to identify as colour varies from a uniform light yellowish brown with almost no distinguishing marks.
  • However, females do have a small dark spot over the centre of the body, on the forewings, visible when at rest .

Egg

  • Usually on the upper surface of plant leaves in batches of 2 – 170.
  • They are flat with a pebbled surface.
  • They overlap each other within the raft to form a smooth mass.
  • Approximately 0.7 mm by 1.0 mm, they are initially white to pale green and change to a paler yellow green as they develop.

Larvae
The identification of larvae is problematic as they are very similar to the larvae of other leaf rollers.

  • The first larval instar [stage] has a dark brown head; all other instars have a light fawn head and prothoracic plate [plate behind the head].
  • Over-wintering larvae are darker.
  • First instar larvae are approximately 1.6 mm long, and final instar larvae range from 10 to 18 mm in length.
  • The body of a mature larva is medium green with a darker green central stripe and two side stripes.
  • The last body segment breathing pores (spiracles) are larger than rest.
  • They spin fine webbing and often occur in leaf rolls or beneath a leaf tied to fruit.

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

Monitoring

Pheromone traps
The flight activity of male moths (along with that of the codling moth, summer fruit tortrix moth and fruit tree tortrix) 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 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.

Caterpillar damage

  • Inspect leaves for evidence of leaf roller activity in May-June.

Fruit damage

  • Inspect 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)’
  • This 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 light brown apple 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.

Chemical control

Several insecticides are approved for control of codling, tortrix moths (light brown apple moth is a tortricid) or caterpillars on apple. As light brown apple moth is a comparatively new pest to Britain we have only limited experience in controlling it with insecticides and comprehensive efficacy trials have not been done.

  • However, experience has shown that indoxacarb (Steward) and methoxyfenozide (Runner) are effective.
  •  Chlorantraniliprole (Coragen) is also thought to offer incidental control when applied against codling moth.
  • On cherry, Bacillus thuringiensis (Dipel) has given disappointing results.
  • Spray programmes applied for control of codling and tortrix moths on apple are likely to give good incidental control of light brown apple moth.
  • However, special control measures may be required if damaging populations of the pest develop.
  • Sprays should be timed according to sex pheromone trap catches.
  • Larvicides should be applied 7-10 days after a threshold catch of 30 moths per trap is reached, with sprays repeated at fortnightly intervals to give protection through the egg hatch period.
  • For details on how to use the various available insecticides, see Fruit tree tortrix moth.

Insecticide resistance

  • Bacillus thuringiensis (Bt) has been used to control light brown apple moth although some populations have become resistant and there is some evidence of avoidance of Bt contaminated food by the larvae.
  • In Australia and New Zealand, light brown apple moth has developed resistance to organophosphate and carbamate pesticides, including chlorpyrifos but no resistance to pyrethroids has been observed.

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 (see ‘Monitoring and Forecasting’).
  • Bt is not detected by conventional pesticide residue analysis.
  • See also ‘Chemical control and Insecticide resistance’.

Natural enemies

The light brown moth has many natural enemies. Parasitic wasps especially reduce populations to comparatively low levels in unsprayed orchards but parasites are less abundant in orchards sprayed with broad-spectrum insecticides. Light brown apple moth larvae and pupae are killed by various parasitoids, predators, and diseases. Spiders and earwigs (Forficula auricularia) are the most important predators. Although much is known about the parasitoids of light brown apple moth in Australia and New Zealand, less is know about the effect on light brown apple moth population in the UK.

Insectivorous birds

  • As with other tortricids, birds probably pay a contributing role in controlling numbers of light brown apple moth, but birds 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 light brown apple moth larvae or pupae, but these are unlikely to have a significant controlling effect.

Predatory insects

  • Earwigs and predatory mirid and anthocorid bugs feed on eggs and young larvae.

Virus diseases

  • Infection by a nuclear polyhedrosis virus has been known to decimate localised light brown apple moth populations.

Biotechnological control

Mating disruption systems for light brown apple moth in apple orchards are used in Australia, New Zealand and the USA and are effective, providing initial moth populations are low.

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.

Further reading

Bradley, S. J., Walker, J. T. S., Wearing, C. H., Shaw, P. W. and Hodson, A. J. 1998. The use of pheromone traps for leafroller action thresholds in pipfruit. Proceedings of the 51st N.Z. Plant Protection Conference, 173-178.
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.