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Apple grass aphid – additional information

Life cycle

  • Overwintered eggs on the bark of apple trees hatch in spring by the green cluster growth stage.
  • The nymphs feed on the undersides of the rosette leaves and amongst the flower buds sometimes invading the flowers during bloom.
  • The first generation is wingless but the second generation is winged.
  • The first winged aphids migrate to grasses in mid-May during blossom.
  • Populations on apple then decline rapidly.
  • In the autumn, winged females return to fruit trees and their wingless progeny (the egg-laying females) mate with winged males returning from grasses.
  • Eggs are deposited on spurs and branches, just before leaf fall.

 

Recognition

Egg
Shiny black and found on the bark of apple trees on rough bark around buds.

Adult
Yellowish green with darker green longitudinal stripes down the body.
Honey tubes short, pale green and flanged at the tip.

Other pests with which the pest may be confused

Green apple aphid: The other aphid species that occurs commonly on apple which has a green colour. However, the green apple aphid is uniformly green and has black, moderately long honey tubes. It tends to form dense colonies in extension growth in mid-late summer.

Common green capsid: Nymphs of the common green capsid are green in colour and superficially resemble apple grass aphid. They also occur at a similar time. However, capsid nymphs are active and fast moving and occur as individuals rather than in colonies. Capsid nymphs cause distinct damage to foliage and fruit.

Monitoring

The severity of infestation of each apple orchard by apple grass aphid should be determined when the pre-blossom pest assessment is done at the green cluster to pink bud growth stage.

  • Inspect at least two blossom trusses on each of at least 25 trees per orchard for infestation by the aphid.
  • Presence of the aphids in a particular truss is often indicated by slight leaf distortion and/or the presence of cast skins on the surface of the rosette leaves.
  • An insecticide treatment for the aphid is justified if the economic threshold of 50% of blossom trusses infested with 5 or more aphids is exceeded.
  • Counts of the wingless aphids on apple trees in late October give a good indication of the likely infestation the following spring.
  • An average of one aphid or fewer per leaf from samples of 20 leaves examined on 8-10 trees across the orchard indicates a potentially light spring infestation.

Forecasting

Useful forecasting models have not been developed for apple grass aphid. However, the pest is usually most abundant when there has been plentiful rainfall in summer and autumn the previous year to encourage growth of grass, the aphid’s summer host.

Cultural and biological control

There are few specific cultural controls for apple-grass aphid. Natural enemies should be encouraged by avoiding the use of broad-spectrum insecticides and by providing flowering plants in and around the orchard. Artificial refuges can be provided for predators. High nitrogen levels in the tree favour apple grass aphid.

Natural enemies

Predatory insects and spiders

  • A wide range of predatory insects, including anthocorid, mirid and nabid bugs, ladybird adults and larvae, hoverfly, predatory midge and lacewing larvae and spiders feed on apple grass aphid in spring.
  • The aphid often provides an important early food source which increases predator numbers for natural regulation of other pest species.
  • Spiders and earwigs are more important as natural enemies of the returning migrants and their offspring in the autumn.

Parasitic wasps

  • The parasitic wasp Monoctonus mali is the most important parasitoid of apple grass aphid, though there are several other less important species including Ephedrus persice, Ephedrus validus, Praon necans, Praon volucre and Trioxys auctus.
  • The parasites lay their eggs (usually singly) in the body of the aphid which continue to feed during the early stages of development of the parasite.
  • The parasites eventually pupate within or beneath the skeleton of the aphid forming a so-called ‘aphid mummy’.
  • Monoctonus mali is a host-specific parasite which has two generations on apple grass aphid in spring before entering a summer diapause when its host begins to migrate to grasses.
  • Although parasitic wasps are common natural enemies of apple grass aphid, they are not usually abundant enough to greatly reduce aphid populations.

Biological control

Biological control approaches have not been developed for apple grass aphid.

 

Further reading

Barbagallo, S., Cravedi, P, Passqualini, E, Patti, I, & Stroyan, H. L. G. 1997. Aphids on the principal fruit bearing crops. Bayer, Milan.123pp

Minks, A. K. & Harrewijn, P. 1987. Aphids, their biology, natural enemies and control. World Crop Pests, Volumes 2A, 2B and 2C. Elsevier, Amsterdam.