Languages

Global menu

The Green pages

Aphids

Ravageurs et maladies
English
Aphids (Aphididae) on a stem.
Photo: André Payette

Onglets

Description

Summary

There are thousands of species of aphids in the world. These tiny, highly prolific insects feed by sucking the sap from a wide range of ornamental and food plants. They form dense colonies on young shoots and under leaves, and also feed on plant stems, bark, roots and fruit. They produce a sweet, sticky substance (honeydew), which attracts ants, wasps and bees and promotes the development of a black fungus known as sooty mould. Their constant pumping of sap weakens plants and causes the leaves to become discoloured and deformed and sometimes to drop prematurely. Aphid feeding may also cause fruit to be deformed and galls to form on some plant species. These insects can also transmit viral diseases.

Signs and symptoms

  • Aphids form dense colonies on young shoots and under leaves, and also feed on plant stems, bark, roots and fruit.
  • Some aphids coat themselves with a waxy, white, cotton-batting- or wool-like substance (woolly aphids); other species cause galls to form on some plant species (gall aphids).
  • Infested leaves turn yellow, wilt, curl, become deformed and may drop prematurely; conifer needles become shrivelled; attacked buds produce deformed leaves, flowers or fruit.
  • The honeydew produced by aphids attracts wasps, bees and ants. Ants may even protect the aphids from their natural enemies in exchange for the sweet liquid.
  • In a heavy infestation, large droplets of the honeydew run from the tree, covering the leaves, trunk, sidewalks and cars underneath it with a sticky substance.
  • A black fungus known as sooty mould forms on the honeydew and interferes with plants' growth.
  • Infested plants appear stunted and weak; large numbers of aphids can kill entire branches.
  • They can also transmit toxins and viruses to plants.

Latin name (genus)

Adelgides, Aphidides, Eriosomatides, Phylloxerides

Host plants

Various house plants, food plants, annuals, perennials, deciduous trees and shrubs and conifers.

Development cycle

Description and life cycle

Aphids belong to order Homoptera, along with leafhoppers, whiteflies and scales. They undergo incomplete metamorphosis (hemimetabolic insects). Their life cycle includes three main stages: egg, larva and adult.

Eggs: Small, black and shiny.

Larvae: Resemble adults, only smaller.

Adults: Soft, pear-shaped body, 1 to 4 mm long. They range in colour from green to red, black, pink, yellow, brown or bluish. Woolly aphids are covered in a waxy, white, cotton-batting- or wool-like substance. The head has two long antennae and an articulated rostrum (mouthparts) for sucking. The thorax has six slender legs. Most adult aphids are apterous (wingless). Winged aphids have two pairs of transparent, membranous wings. The abdomen has a sort of tail (cauda), through which the honeydew flows, and sometimes two tubes (cornicles), used for defence.

Aphids have a complex and unusual life cycle. Some aphids spend their entire life on the same plant, while others must change host plants to complete their life cycle.

Some species reproduce sexually, while others multiply solely by parthenogenesis (without fertilization by a male).

In temperate regions, aphids usually overwinter as eggs, hidden between the scales on buds, in cracks in bark or underground. Some ants that raise aphids for their honeydew shelter the eggs in their nests in winter. In spring, they transport them to host plants.

When the overwintered eggs hatch in spring, the first generation consists only of apterous (wingless) females. Once they mature (in approximately 8 days at 20°C), they do not need to be fertilized and, rather than laying eggs, give birth, by parthenogenesis, to tiny wingless female aphids. During their short lives (20 to 30 days), each female can produce from 40 to 100 aphids, which continue to reproduce in the same way.

Over the summer, winged females appear periodically and move to other plants to form new colonies.

In fall, the females give birth to winged males and wingless females. After mating, the fertilized females lay one to four eggs, attaching them to the stems of host plants or gaps in bark and buds. These eggs hatch the following spring.

There are several generations each year.

Prevention and control

Favourable conditions

Aphids flourish during warm summers and tend to proliferate after mild falls and winters. Drastic pruning and the use of high-nitrogen or fast-acting fertilizers promote the rapid growth of tender shoots, which attract aphids.

Identification

Starting in spring, inspect plants regularly to identify aphids before they cause too many problems. Closely examine the underside of leaves and the tips of new shoots. The presence of honeydew and the comings and goings of ants may also point to an aphid problem.

Prevention

  • Scrupulously inspect all new plant purchases to avoid introducing any intruders into your garden.
  • Keep plants vigorous fertilizing them adequately, pruning them properly and watering them during dry spells.
  • Avoid drastic pruning and heavy feeding with high-nitrogen fertilizer, both of which promote excess growth of tender shoots.
  • Intersperse the plants in borders with a few bait plants (good ones are nasturtiums and petunias) to attract and trap aphids; destroy and replace these plants regularly.
  • Remove weeds regularly, because they may serve as host plants.

Physical control

  • Dislodge aphids by spraying them with a hose; repeat this treatment as necessary.
  • Remove and dispose of all heavily infested stems and leaves; crush groups of insects on a plant by hand.

Biological control

  • Aphids have many natural predators (ladybird beetles, lacewings, syrphid fly larvae, spiders, birds, braconids, etc.). Encourage these predators by growing a wide variety of plants. Plant species that attract aphid insect predators, including tansy, marigold and calendula.
  • It is not recommended that you purchase ladybird beetles to control aphids in an outdoor garden, because the adults are apt to fly away.

Chemical control

As a last resort, use a low-impact pesticide with insecticidal soap as the active ingredient. Read the product label carefully and follow the manufacturer's recommendations.

 

Further reading: Aphids on Insects and other arthropods.

Add this

Share this page