Life cycle

• Overwintered eggs are laid under loose bark or in deep crevices in the bark of the main trunk and branches of the tree.
• The eggs hatch in spring at early green cluster and colonies develop on the undersides of the rosette leaves.
• Later, infestations develop in the young shoots.
• In the third generation, winged and wingless females are produced and in the fourth generation, winged males but wingless females.
• These sexual forms mate and eggs are laid from mid-June to mid-July.
• Colonies die out in mid-summer, most live aphids disappearing by the end of July.
• There is no evidence of infestations spreading from tree to tree by winged migrants.
• Spread from tree to tree is slow and may be caused by walking aphids.

Pest status

A minor pest of apple.

Other hosts

Only breeds on apple and some Malus sp.

Varietal susceptibility

• Some apple varieties are resistant to rosy leaf curling aphid, notably Cox.
• Others, such as Bramley, are susceptible and some, notably Golden Delicious and Worcester Pearmain are highly susceptible.
• The single gene responsible for resistance has been identified and is now used in apple breeding programmes.
• At East Malling Research, where the resistance gene was first identified, all recently released new varieties have included the resistance gene.

Distribution

Widely distributed but local, often occurring on the same few trees in an orchard in successive years.

Recognition

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

Adult
Grey to dark bluish grey, dusted with a white waxy powder and with short, black, tapering honey tubes which are flanged at the tip.

Other pests with which rosy leaf curling aphid may be confused

Rosy apple aphid

• The adult aphid and nymphs of rosy apple aphid and rosy leaf curling aphid are very similar in appearance.
• Both pests cause leaf curling but the rosy apple aphid does not cause the bright red coloration of leaves which is only caused by the rosy leaf curling aphid.

Apple leaf curling midge

• Curling of leaves in the shoot tips is often caused by larvae of the apple leaf midge and the leaf curls often develop a reddish colour.
• However, leaves damaged by this pest are tightly curled, often upwards, and contain small, white or pinkish maggot like larvae of the apple leaf midge.

Monitoring

The severity of infestation by rosy leaf curling aphid should be determined in each orchard when pest assessments are done before blossom at the green cluster to pink bud growth stage.

• Attention should be focussed on highly susceptible varieties (e.g. Golden Delicious) and in places where the pest occurred the previous year.
• Examine the rosette leaves over the whole tree on at least 25 trees per orchard.
• Localised application of an insecticide to control green apple aphid should be considered where infestation is detected.

Forecasting

Forecasting models for rosy leaf curling aphid have not been developed.

Control methods

Chemical control

A localised application of an approved insecticide should be considered where the pest is detected.

• If only rosy leaf curling, rosy apple or apple grass aphid are to be controlled, then  flonicamid (Mainman) is likely to be a good choice as it is a selective aphicide.
• A full approval for spirotetramat (Batavia) on apples for the control of sucking insect pests will control rosy leaf curling aphid, but growers may prefer to reserve its use for more difficult to control pests such as woolly aphid. It must be applied after flowering and works best when pests are moving from brown 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’.
• The neonicotinoid acetamiprid (Gazelle) is also likely to be effective against rosy leaf curling aphid although its activity against other apple pests has not been explored sufficiently widely. It is known to control mussel scale very effectively when applied at the correct time for the pest at 90% crawler emergence.
• Earwigs are important natural enemies.

Note that these materials are largely ineffective against winter and tortrix moth caterpillars.

• The synthetic pyrethroid insecticide deltamethrin (Decis Forte etc) is also approved for control of aphids on apple but its use should be avoided as it is harmful to predatory mites and other insects.

It is important to apply insecticides in warm weather conditions at the full recommended dose and in a sufficient spray volume to give adequate cover.

It is also important to apply the insecticide early, before large colonies form which are difficult to control once surrounded by distorted mature leaves.

Cultural control

Rosy leaf curling aphid is a pest that occurs on the same trees year after year and only spreads slowly to adjacent trees.

• Where infestation is on a limited scale, it may be practical to remove and destroy infested shoots.
• 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 should be used to foster earwigs and other natural enemies such as lacewings.
• 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

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 rosy leaf curling aphid.

Parasitic wasps

• The parasitic wasps Ephedrus persice, Ephedrus platigator and Trioxys angelicae are known to parasitise rosy leaf curling aphid.
• The parasites lay their eggs (usually singly) in the body of the aphid which continues to feed during the early stages of development of the parasite.
• The parasite eventually pupates within or beneath the skeleton of the aphid, forming a so-called ‘aphid mummy’.
• Although parasitic wasps are common natural enemies of rosy leaf curling aphid, they are not usually abundant enough to greatly reduce aphid populations.

Fungal parasites

• Outbreaks of fungal diseases (Entomophthora sp.) probably occur in rosy leaf curling aphid colonies. Outbreaks occur in warm, humid or wet conditions.

Biological control

Biological control approaches have not been developed for rosy leaf curling 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.