Aphids

Aphids are small, pear-shaped insects that may be green, black, yellow, pink, or grey depending on species. A distinctive feature is a pair of tube-like structures (cornicles) projecting from the rear of the body. Colonies are often found on new growth and the undersides of leaves.

Signs of infestation include clusters of insects, sticky honeydew on leaves and surfaces below, black sooty mould growing on the honeydew, and distorted or curled young leaves.

Many aphids have complex life cycles. During favourable conditions, females often reproduce without mating and give birth to live young, allowing populations to increase very rapidly. Winged forms are produced that disperse to new plants, which is important both for spread and for virus transmission.

Life cycles and host relationships vary widely among species, and some alternate between different host plants at different times of year.

Aphids damage crops in several ways: direct removal of sap can weaken plants and distort growth; honeydew and sooty mould reduce photosynthesis and can affect quality; and, most importantly for many crops, aphids transmit plant viruses as they feed.

Host crops include cereals such as wheat, many vegetables including tomato and potato, and a wide range of other plants. The economic importance of aphids varies greatly by crop, region, and the viruses present.

Regular scouting is central to aphid management. Monitoring the presence, abundance, and location of colonies — and the activity of natural enemies — informs whether and when action is warranted, using local economic thresholds where they exist.

Aphid management fits within integrated pest management, which combines several approaches rather than relying on any single tactic.

• Conserve natural enemies such as ladybirds, lacewings, and parasitoid wasps
• Use resistant or tolerant varieties where available
• Manage nitrogen and growth to avoid excessively lush, attractive foliage
• Monitor and use local thresholds to guide any intervention