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BYDV aphids

Barley Yellow Dwarf Virus and Aphids | Aphid feeding damage and control

Aphid species | Life cycle

Aphids can affect cereals not only by spreading barley yellow dwarf virus (BYDV) but also when in sufficient numbers by direct feeding on plants. Several species may be involved and their life cycle can involve several plant hosts.

Aphid species

Oat aphid (Rhopalosiphum padi) and corn aphid (R. maidis) cause most yield loss and are also the primary vectors of BYDV.  Wingless aphids are about 0.2 to 2.5mm long.  Rice root aphid (R. rufiabdominalis) and Sitobion miscanthi (no common name) are also sometimes found in cereal crops but usually in much lower numbers.

Oat aphids

• Despite their name, oat aphids can be found on all cereals including wheat, barley and oats. 
• They vary from mottled yellow-green through olive-green and dusky brown, to a blackish green, and are characterised by a dark reddish patch on the tip of the abdomen. 
• Adults are usually pear-shaped. 
• Colonies develop on the outside of tillers from the base upwards, on stems, nodes and backs of mature leaves, starting any time between seedling stage and grain filling. 
• Generally they tend to stay on the lower parts of the plant.  However, heavy infestations can blacken heads and flag leaves, and this is the most abundant species in most years. 
• Oat aphids are more mobile than corn aphids, and can drop to the soil and crawl to other plants.
• Oat aphids are the most important vectors of BYDV.

Corn aphids

• Corn aphids are more likely to be found in barley than in wheat and they are also often found in summer sorghum crops. 
• They are dark blue-green to grey-green, sometimes with a waxy look.
• They usually look rectangular or elongated in shape. 
• Colonies generally develop within the furled emerging leaves of tillers, starting any time from seedling stage to head emergence, and they can be difficult to see. 
• They can be important vectors of BYDV when they arrive early enough in crops.

Sitobion miscanthi

• Adult aphids are noticeably large (compared with the other cereal aphids) with long legs and antennae.
• All growth stages are coloured light green with yellow-green tinges along their backs. 
• Sitobion miscanthi are not usually found until spring, and generally settle on upper leaves and on the ear; they seldom develop large colonies. 
• They are not considered to be important vectors of BYDV

Rice root aphids

• These are similar to oat aphids, and can infest plant roots, although they are usually found at the base of the plant stem. 
• They have a reddish patch in the middle of the back, and are most likely to be found in drier agricultural areas. 
• Generally they are not found in large numbers and are not considered to be major vectors of BYDV.

Rose-grain aphids

Are potentially serious pests, but are yet to enter Western Australia from the eastern States where they are widespread. They are pale green to yellow coloured, spindle-shaped aphids attacking wheat and barley during grain filling.

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Life cycle

• Winged cereal aphids fly into crops from grass weeds, pasture grasses or other cereal crops, and colonies of aphids start to build up within the crop. 
• In Western Australia, all aphids in a cereal crop are females, able to give birth to live young without the need to mate.  (In colder countries male aphids are also produced and aphids may over-winter as eggs produced by sexual reproduction.)  
• Reproduction is rapid when weather conditions are favourable, leading to population outbreaks.  Cold conditions slow the rate of development and movement. 
• The young "nymph" aphids go through several growth stages, moulting at each stage into a larger individual.  Sometimes you can see the delicate pale aphid skins or "casts" after they are shed. 
• Nymphs do not have wings. 
• In good conditions most adults will also be wingless and are called apterae.  
• When plants become unsuitable or overcrowding occurs, winged aphids, called alatae, develop and migrate to other plants or crops.

Page reviewed: 13 April 2005