|Scientific Name||Sitobion avenae (Fabricius, 1775)|
|Common Names||English: Grain aphid; German: Große Getreidelaus ; Spanish: Pulgón del trigo; French: Puceron des épis de céréales|
Adults are up to 3 mm in length. The body color is determined partly genetically, and partly by the environment (especially food quality). Most clones tend to be yellowish to dark green or brown, or sometimes orange-pink.
The antennae, cornicles and some parts of the legs are black. Alates have a wingspan of about 6-9 mm.
On young cereal plants, these aphids colonize the leaves and stalks. When heading begins, they migrate towards the ears and settle among the bracts and kernels. In contrast to some other aphids, large populations of S. avenae in the ears may cause significant direct damage, particularly if heavy infestation occurs between heading and the milky-ripe stage, because feeding leads to a reduced number of well-established grains, and the developing kernels become shrunken and malformed. This results in a reduction in thousand-grain weight and overall yield.
At other stages of plant development, damage is usually indirect. Large colonies of the aphids will produce copious amounts of honeydew, promoting the growth of sooty molds, which impedes photosynthesis and thus aggravates the effects of nutrient removal with the plant sap ingested by the insects.
In many regions, the grain aphid is an important vector of plant viruses that may cause considerable injury, the most important among them being BYDV, which it transmits persistently.
The reproductive strategy of S. avenae depends on climatic conditions. In milder climates, it is completely anholocyclic, i.e. there are only parthenogenetic females, even during the cool season. However, these cannot withstand low temperatures for a long period, so the holocyclic lineages are frequently found in colder parts of the aphid's range. Here, sexual morphs appear in autumn and then mate: the oviparae produce 6-9 eggs each, which then overwinter. The areas of the two lineages overlap to a great extent, so both strategies can be found coexisting at a location.
This species is effectively monoecious, as its earlier primary host (Gen. Rubus) has virtually been abandoned.
During the warm season, population growth can be very rapid. Each female produces several larvae a day over a period of approx. 3-4 weeks. The larvae pass through four instars over an 8-12 day period and later give birth to new generations.
The viviparous morph is usually wingless and disperses only by crawling. When environmental conditions become unfavourable, e.g. as feeding sites become overcrowded and food becomes scarce (because grains become dried and hardened), winged forms may appear that then migrate through the field and can often be transported over large distances, if carried by the wind.
S. avenae is widespread in the different climatic regions of the world, except the subtropics and tropics.
Additional Crop Information
Most important economically as a pest of wheat.
The high reproductive potential of aphids under favorable conditions means that outbreaks can cause considerable damage, especially in wheat. Virus transmission is a threat even at low population densities.
Integrated Crop Management
Late sowing in autumn will help to avoid population build-up before winter.
As with all aphids, natural enemies play an important role in the regulation of populations of this species. Insecticides with beneficial-friendly profiles should be chosen. Preserve landscape elements such as boundary ridges and hedgerows that can serve as reservoirs for predatory insects. Healthy, vigorous plants can tolerate aphid infestations much better.
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