Aphids

In a nutshell:

Many different pest species; wide variety of host plants; sap suckers—cause leaves to yellow, excrete sticky “honeydew”; rapid reproduction; viral disease vectors.

Fight them with: Please consult the ID guide for species-specific information.

What are aphids?

Aphids form a single, very large group of insects with over 4 000 identified species; around 250 species are considered pests. They’re all sap suckers that can reproduce asexually (unfertilized females give birth to genetically identical offspring). This means that populations can grow very quickly. Aphids also transmit many different viruses that cause disease in plants.

What kinds of plants do they attack?

Aphids attack a wide variety of both vegetables and ornamental plants. Some species may have specific preferences, please consult the ID guide for species-specific information.

What do they look like?

Aphids have a complex life cycle that includes both winged and wingless adult forms of the same species, as well as both sexual and asexual reproductive stages. Winged forms develop in response to changing environmental conditions or overcrowding.

In greenhouses, aphids are often in a continuous state of asexual reproduction and the population will consist entirely of female clones. Every day an asexual female can give birth to between three and ten fully developed nymphs, which begin feeding on plant sap immediately.

These nymphs have the exact same appearance as the adults but are smaller in size. They grow rapidly and shed their skin four times before they are fully grown, leaving white moults behind.

Please consult the ID guide for species-specific information.

How do I know if my plants are under attack?

Different species of aphid can cause different kinds of damage. But, you may have an aphid infestation if you observe the following signs and symptoms:

  • White skin moults appear on the underside of leaves; aphids may be present in visible colonies if the population is large enough.
  • Deformed leaves and growing tips as well as defoliation are caused by both nymphs and adults sucking vital sap. This can lead to death in young plants, and substances in aphid saliva also disrupt normal plant growth.
  • Excess sugar from the sap is excreted on leaves and fruit surfaces as a sticky “honeydew”. Black fungal moulds will often grow on this substance, reducing photosynthesis and contaminating fruit.

Aphids can also transmit diseases, viruses in particular, between plants; Potato virus Y and cucumber mosaic virus are commonly transmitted this way.

Please consult the ID guide for species-specific information.