Schizaphis graminum

Scientific Name Schizaphis graminum Rondani
Synonyms Toxoptera graminum, Rhopalosiphum graminum
Common Names English: Greenbug; German: Grüne Getreideblattlaus; Spanish: Pulgon de las gramineas; French: Petit puceron des cereales
Description The body of this aphid is pear-shaped, about 1.5 to 2.0 mm (0.06-0.08 inch) long and yellowish-green in color, with a darker stripe running along the back. The tips of the siphunculi and the legs are almost black, as are the antennae, which are more than half as long as the body.

Biology

Damage

Like other aphids, Schizaphis graminum ingests phloem sap with its piercing-sucking mouthparts. This weakens the plant due to loss of nutrients and water. Moreover, the saliva the greenbug injects while feeding contains enzymes that disintegrate cell walls and chloroplasts and therefore have a toxic effect on the plant tissues. The necrotic lesions this causes appear as small yellow or reddish spots around the punctures. As feeding continues, these soon coalesce into larger patches. Eventually, the whole leaf will wilt and the plant may be killed off completely.

High densities of greenbugs significantly lower the plants' photosynthetic activity, resulting in stunting and reduced yield. Infestation is particularly dangerous during stem elongation. After tillering, the additional damage is seldom significant. The aphids prefer to settle on the undersides of older, lower leaves, which their colonies may cover completely in severe cases. On expanding, the colonies gradually move upwards on the plant. Greenbug damage is often apparent in the field as circular patches that slowly grow in size. S. graminum is an important vector of Barley Yellow Dwarf, Sugarcane Mosaic and Maize Dwarf Mosaic Viruses.

Lifecycle

Schizaphis graminum is facultatively holocyclic, i.e. in cold climates, it may reproduce sexually in the cool season and lay eggs that are able to withstand low temperatures; but where winters are mild, it will propagate parthenogenetically throughout the whole year. During its lifespan of 3-4 weeks, each apterous virginoparous female will produce 2-3, sometimes up to 5 live young per day. After molting 3 times in 6-10 days, these nymphs are mature and are able to give birth themselves. Under favorable conditions - mild, dry weather, abundance of food, low activity of parasitoids and predators - population densities can increase rapidly. When crowding occurs or food becomes limited, winged females appear and spread to other plants.

In cool regions, sexual morphs are produced in the autumn, a process triggered by declining temperatures and daylight time. After mating, the female lays eggs into leaf sheaths of winter cereals or other grasses: 10-12 in groups of 2-4 over a period of 4-5 weeks. In contrast to other aphids, S. graminum has no change of host. In the spring, wingless females hatch from the eggs: after 1-3 weeks, they give birth to live young and asexual reproduction starts again. There are several biotypes of greenbug that differ greatly in terms of host preference, temperature tolerance and their ability to overcome plant resistance. They have, however, no approved taxonomic status. S. graminum has a bacterial endosymbiont (Buchnera aphidicola) that plays an important role in the insect's amino acid metabolism.

Occurrence

Additional Crop Information

Important hosts of S. graminum are sorghum and wheat in particular, but also barley, corn, millet, oats, rice and rye

Agricultural Importance

This aphid is probably of palearctic origin, but is nowadays found worldwide in almost all cereal-growing regions. The winged forms are frequently carried over long distances by air currents. Greenbug is considered one of the most serious pests of cereal crops in many countries.

Control

Integrated Crop Management

Schizaphis graminum has a great number of natural enemies. While these will not always provide sufficient control, their elimination by inappropriate use of broad-spectrum pesticides can exacerbate outbreaks of this pest. Crops receiving an adequate water supply will be much less susceptible to greenbug damage.

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