Life cycle

• Overwintered eggs on the bark of apple trees hatch in April, rather later than those of the apple grass aphid or the rosy apple aphid.
• The nymphs feed on the undersides of the leaves mainly in the tips of young shoots. Winged aphids develop in June and throughout the summer.
• The winged aphids migrate to other apple trees and these are largely responsible for the colonies that develop in extension shoots in summer. Wingless sexuals form in the autumn and eggs are laid on the bark of young shoots, often in considerable numbers.
• Colonies are usually attended by the common black ant Lasius niger, which feeds on the honeydew produced by the aphids but also defend the colonies from attack by natural enemies.

Pest status

Green apple aphid is a common but minor pest of apple which also attacks pear. It is most important on young trees.

Other hosts

Pear and quince are also attacked.

Varietal susceptibility

All apple varieties are susceptible to infestation by the aphid.

Distribution

Widespread and common.

Damage

Spring attacks are unimportant. Large colonies may develop in the shoots in summer, causing considerable leaf curl, stunting and shoot tips may be killed.

• This damage is important on nursery stock and young trees. In established orchards, infestation of up to 10% of shoots can be tolerated (see ‘Monitoring’).
• However, if colonies are large, fruit beneath may be contaminated with honeydew and cast skins.
• Colonies are usually attended by the common black ant Lasius niger, which feeds on the honeydew produced by the aphids and helps to prevent contamination of the foliage.

Recognition

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

Adult
Bright or yellowish green. Honey tubes (siphunculi) moderately long (about the same length as the distance between their bases), black or dark brown. Cauda (‘tail’) finger-like.

Other pests with which the pest may be confused

Apple grass aphid

• This is the other aphid species that occurs commonly on apple and which has a green colour.
• However, the apple grass aphid has darker green longitudinal stripes and has pale green, short (much shorter than the separation between their bases), honey tubes which are flanged at the tip.
• Apple grass aphid is abundant on the rosette leaves and amongst trusses from green cluster to shortly after blossom whereas the green apple aphid is more troublesome in summer.

Monitoring

The severity of infestation by green apple aphid should be determined in each orchard when pest assessments are done from late June to the end of August.

• Examine the growing shoots (preferably all, but examining two shoots per tree carefully) in at least 25 trees per orchard.
• Application of an insecticide to control green apple aphid should be considered if more than 30% of shoots are infested with one or more aphids or if 10% of shoots have infestations causing leaf curling.

Forecasting

Useful forecasting models for green apple aphid have not been developed.

Chemical control

Control of infestations in shoots in summer
A spray of an approved insecticide should be applied as soon as damaging infestations are detected (see ‘monitoring’).

• Many insecticides are approved for control of aphids on apple but if aphids are the only pests that need to be controlled, flonicamid (Mainman) is the preferred choice in conventional orchards as it is selective and partially systemic.
• The neonicotinoid acetamiprid (Gazelle) is also highly effective. It will also control various other pests such as mussel scale.
• A full approval for spirotetramat (Batavia) on apples for the control of sucking insect pests will control green apple aphid, but growers may prefer to reserve its use for more difficult to control pests such as woolly aphid and rosy apple aphid. It must be applied after flowering and works best when pests are moving from brown wood to green tissue. It will prevent population build-up but does not offer pest ‘knockdown’.
• A recent EAMU for Flipper (fatty acids) has increased the available options should growers wish to reserve other insecticides for control of pests later in the season. It is known to complement the use of Batavia as it provides quick ‘knockdown’.
• Use of synthetic pyrethroids, which are harmful to natural enemies, should be avoided.

Control from applications of aphicides in spring

• A spray of an approved insecticide is often applied before blossom at the green cluster to pink bud growth stage against rosy apple aphid and/or apple grass aphid.
• Such applications will also control green apple aphid present at that time and will reduce, but not eliminate, the number of colonies that develop from winged migrants in summer.

Cultural control

There are few specific cultural controls for green apple 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 and other factors that favour vigorous shoot growth favour green apple aphid and should be avoided.

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 green apple aphid.
• However, the black ant, Lasius niger, is usually attendant in green apple aphid colonies and defends them from predators.

Parasitic wasps
The parasitic wasp Trioxys angelicae is the most important parasitoid of green apple aphid, though the aphid is parasitised by many other species including Ephedrus persice, Ephedrus platigator, Lipolexis gracilis, Lysiphlebus fabarum, 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’. Trioxys angelicae also parasitises rosy apple aphid and rosy leaf curling aphid.
• Although parasitic wasps are common natural enemies of green apple aphid, they are not usually abundant enough to greatly reduce aphid populations.

Fungal parasites:
Outbreaks of fungal disease (Entomophthora planchoniana and E. fresenii) have been recorded in green apple aphid colonies. Outbreaks occur in warm, humid or wet conditions.

Biological control

Biological control approaches have not been developed for green apple 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.