Birdcherry-oat aphid

Rhopalosiphum padi

Description
The body of the adult is about 1.0-2.5 mm (0.039-0.097 inch) in length, orange-green to olive green or occasionally nearly black in color, and has a typical orange-red band around the cornicles.

Damage
Like all aphids, R. padi uses its piercing-sucking mouthparts to penetrate plant tissues in order to reach a vascular bundle and ingest phloem sap. Although this species can remove considerable amounts of liquid and nutrients, and strong infestations can sometimes lead to contortion of leaves, the direct effect on grain yield is generally only slight, especially if plants are young at the time of infestation. The insect causes most damage by transmitting a number of viruses, especially Barley Yellow Dwarf Virus (BYDV), for which it is the most important vector.

Infection with BYDV causes barley and wheat to turn yellow, whereas oats becomes reddish in color. Affected plants are generally severely stunted and non-productive. The resulting losses in grain yield and quality can be considerable.

Phloem sap only contains small amounts of the amino acids the aphids need, so they must consume large volumes of it, meaning that they subsequently have to excrete excess liquids and sugars. If population densities are high, this excretion (called „honeydew“) can create a sticky film on plant surfaces that can reduce photosynthesis and promote the growth of sooty mold.

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