Aphids in citrus

Four species of aphids on citrus are recorded in Australia but only two occur in Western Australia, the brown/black citrus aphid Toxoptera citricidus (Kirkaldy) and spiraea aphid, Aphis spiraecola Patch.

Like other sap-sucking insects such as mealybugs and scales, aphids produce a sticky substance (honeydew) as they feed on the plant.

A black fungus (sooty mould) grows on the honeydew, coating leaves, branches and fruit with a black powder. Aphids can be a threat to young trees, but are otherwise regarded as minor pests.

Damage

  • All aphids have a piercing-sucking mouthpart (stylet) that they insert into the plant tissue to feed on leaves, green shoots and flowers. Leaves may curl as a result of feeding damage.
  • Large quantities of honeydew are also produced as the aphid feeds. Leaves and fruit often turn black with the growth of the sooty mould fungus.
  • Aphids are not usually a problem in citrus, except on young trees.
  • Overseas, black citrus aphid has been associated with the spread of citrus tristeza virus which causes dieback.

Life cycle

  • Females do not need to mate to produce young and no eggs are laid. Live young are produced through a process termed parthenogenesis.
  • Female aphids are born pregnant and adult females can be wingless or winged.
  • Winged forms indicate that the food quality has declined, or that there is overcrowding.

Citrus aphids and predatory ladybug

Brown citrus aphids

Brown/black citrus aphid 

The scientific name is Toxoptera citricidus (Kirkaldy).

Distribution and description

This aphid is found in all Western Australian citrus growing areas.

  • Nymph: pear-shaped, red-brown, brown to black, 1-2mm long
  • Adult: shiny black, 2mm long, winged or wingless.

Life cycle

  • An entire generation can develop in one week.
  • Nymphs mature in six to eight days at temperatures of 20ºC or above. A single aphid can produce a population of over 4400 in three weeks in the absence of natural enemies.
  • 25–30 generations per year.

Monitoring

Young trees from February to March and then again September to December.

Action level

25% or more of leaf flushes infested with aphids.

Spiraea aphid

Spiraea aphid

Spiraea aphid 

The scientific name is Aphis spiraecola Patch.

Distribution and description

Found in Harvey though may be present in other growing areas. Regarded as rare in WA citrus.

  • Nymph: pear-shaped, apple green to bright yellow, 2mm long
  • Adult: apple green, 2mm long, winged or wingless.

Life cycle

An entire generation can develop in one week, with females each producing 60 young.

  • Up to 25 generations per year.

Monitoring

Young trees from February to March and September to December.

Action level

25% or more of leaf flushes.

Management

Hover fly larva feeding on aphids. Photo courtesy Pia Scanlon, DAFWA

Hover fly larva feeding on aphids. Photo courtesy Pia Scanlon, DAFWA

Chemical control

  • Natural enemies normally keep aphid populations under control. Chemical control is rarely required.
  • Use a specific aphicide or horticultural spray oil.
  • Always check the label before spraying, as not all oils are registered for use in citrus. Oils can also cause phytotoxic damage if not used correctly.

Biological control

  • Predators, parasites, and fungal diseases all attack aphids and occur naturally in the orchard. The honeydew produced by the aphids provides a good food source for many natural enemies.
  • Aphid parasites include the wasp genera Aphidius and Aphelinus: neither is available commercially. The female wasps lay their eggs individually inside the lower part of the abdomen of young nymphs. The parasitised nymphs appear bloated and bronze in colour.
  • Aphids are attacked by many generalist predators include hoverfly larvae (syrphids), ladybird beetles and lacewing larvae.

Contact information

Sonya Broughton
+61 (0)8 9368 3271
Page last updated: Friday, 10 October 2014 - 12:46pm

Author

Sonya Broughton