The Russian wheat aphid (''Diuraphis noxia'') is an

aphid Aphids are small sap-sucking insects in the Taxonomic rank, family Aphididae. Common names include greenfly and blackfly, although individuals within a species can vary widely in color. The group includes the fluffy white Eriosomatinae, woolly ...

that can cause significant losses in cereal crops. The species was introduced to the

United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...

in 1986 and is considered an

invasive species An invasive species is an introduced species that harms its new environment. Invasive species adversely affect habitats and bioregions, causing ecological, environmental, and/or economic damage. The term can also be used for native spec ...

there. This aphid is pale green and up to 2 mm long. Cornicles are very short, rounded, and appear to be lacking. There is an appendage above the cauda giving the aphid the appearance of having two tails. The

saliva Saliva (commonly referred as spit or drool) is an extracellular fluid produced and secreted by salivary glands in the mouth. In humans, saliva is around 99% water, plus electrolytes, mucus, white blood cells, epithelial cells (from which ...

of this aphid is toxic to the plant and causes whitish striping on cereal leaves. Feeding by this aphid will also cause the flag leaf to turn white and curl around the head causing incomplete head emergence. Its host plants are cereal grain crops including

wheat Wheat is a group of wild and crop domestication, domesticated Poaceae, grasses of the genus ''Triticum'' (). They are Agriculture, cultivated for their cereal grains, which are staple foods around the world. Well-known Taxonomy of wheat, whe ...

and

barley Barley (), a member of the grass family, is a major cereal grain grown in temperate climates globally. It was one of the first cultivated grains; it was domesticated in the Fertile Crescent around 9000 BC, giving it nonshattering spikele ...

and to a lesser extent, wild grasses such as

wheatgrass Wheatgrass is the freshly sprouted Cotyledon, first leaves of the Wheat, common wheat plant (''Triticum aestivum''), used as a food, drink, or dietary supplement. Wheatgrass is served Freeze-drying, freeze dried or fresh, and so it differs from ...

es, brome-grasses, ryegrasses and anything in the grass family. The Russian wheat aphid is native to southwestern parts of Asia. It was introduced to many countries in

Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...

and

Africa Africa is the world's second-largest and second-most populous continent after Asia. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 20% of Earth's land area and 6% of its total surfac ...

. It was first found in the U.S. in 1986 in

Texas Texas ( , ; or ) is the most populous U.S. state, state in the South Central United States, South Central region of the United States. It borders Louisiana to the east, Arkansas to the northeast, Oklahoma to the north, New Mexico to the we ...

. The species was probably transmitted through wheat imports.

Pest

Russian wheat aphids are one of the most significant pests on wheat in the world. It was first identified as a pest in

Crimea Crimea ( ) is a peninsula in Eastern Europe, on the northern coast of the Black Sea, almost entirely surrounded by the Black Sea and the smaller Sea of Azov. The Isthmus of Perekop connects the peninsula to Kherson Oblast in mainland Ukrain ...

in 1901. And the origin of ''D. noxia'' can be traced back to Eurasia when it was a pest on cereals. Aside from direct damages to crops, they are also vectors for

barley yellow dwarf Barley yellow dwarf (BYD) is a plant disease caused by the ''barley yellow dwarf virus'' (BYDV), and is the most widely distributed viral disease of cereals. It affects the economically important crop species barley, oats, wheat, maize, triticale ...

, barley mosaic and sugarcane mosaic viruses. After its detection in the US in 1986, the Russian wheat aphid quickly became a major pest of wheat and barley. The researches that found ''D. noxia'' resistant strains of wheat were in 1996 but

genotype The genotype of an organism is its complete set of genetic material. Genotype can also be used to refer to the alleles or variants an individual carries in a particular gene or genetic location. The number of alleles an individual can have in a ...

s of aphids that were able to overcome these resistance strains began to appear in 2003. ''D. noxia'' feeds on the host plant through the

phloem Phloem (, ) is the living tissue in vascular plants that transports the soluble organic compounds made during photosynthesis and known as ''photosynthates'', in particular the sugar sucrose, to the rest of the plant. This transport process is ...

. The result of being a host of an aphid are damages through nutrient drainage which develops into symptoms such as

chlorosis In botany, chlorosis is a condition in which leaves produce insufficient chlorophyll. As chlorophyll is responsible for the green color of leaves, chlorotic leaves are pale, yellow, or yellow-white. The affected plant has little or no ability to ...

necrosis Necrosis () is a form of cell injury which results in the premature death of cells in living tissue by autolysis. The term "necrosis" came about in the mid-19th century and is commonly attributed to German pathologist Rudolf Virchow, who i ...

wilting Wilting is the loss of rigidity of non-woody parts of plants. This occurs when the turgor pressure in non- lignified plant cells falls towards zero, as a result of diminished water in the cells. Wilting also serves to reduce water loss, as it ...

, stunting and other growth impairment. The aphid further increases the nutritional drainage of the host plant through eliciting an increase in essential

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although over 500 amino acids exist in nature, by far the most important are the 22 α-amino acids incorporated into proteins. Only these 22 a ...

in the phloem

sap Sap is a fluid transported in the xylem cells (vessel elements or tracheids) or phloem sieve tube elements of a plant. These cells transport water and nutrients throughout the plant. Sap is distinct from latex, resin, or cell sap; it is a s ...

by triggering a breakdown of proteins in the host plant.

Effect of Aphid infestation

''D. noxia'' has a variety of effects on the host plant and the subsequent product for which the plant is used. The host plants response to an aphid infestation is a loss of

turgor Turgor pressure is the force within the cell that pushes the plasma membrane against the cell wall. It is also called ''hydrostatic pressure'', and is defined as the pressure in a fluid measured at a certain point within itself when at equilib ...

and reduced growth due to water imbalances as the aphid feed on phloem. The aphid also causes reduction in

biomass Biomass is a term used in several contexts: in the context of ecology it means living organisms, and in the context of bioenergy it means matter from recently living (but now dead) organisms. In the latter context, there are variations in how ...

of the whole plant. However, once the aphid is removed the plant quickly recovers absolute growth rate and has increased relative growth. As a result of previous infestation, the recovering plants are more efficient in carbon assimilation that results in increased relative growth rates and compensates for the leaf damages during aphid infestation. Aphid infestation on wheat also affects the flour that is made from infested wheat plants. Aphid feeding in wheat results in qualitative and quantitative losses in flour yield. Flour derived from aphid infested wheat has a significant negative effect on the gliadin/glutenin ratio which reduces the bread making quality of aphid infested wheat plant flour. However, although it does reduce the quality of flour for bread-making, it is still within acceptable ranges to be usable.

Cold resistance

As ''D. noxia'' became an invasive species in North America, it is notable that they possess enough endurance to cold temperatures to survive through winter. Aphid populations can overwinter through temperatures between 0 and 5 degrees Celsius. However, temperatures below 10 degrees Celsius will lead to catastrophic decrease in population. In addition to survivability in sub zero temperatures, the aphids are also capable of rapid cold hardiness (RCH) which allows an insect to develop protection against sudden sub freezing temperatures. Moreover, aphids are capable of RCH without any cost to their reproductive capability.

Management

Tolerance

A method to control ''D. noxia'' infestation of wheat and barley is through host control. Host control consists of raising crops that possess genes that may contribute to aphid resistance. Research has been conducted to identify the specific genes that can be attributed to aphid resistance and the information marked to assist in breeding aphid resistant strain of wheat or barley. The genes that have been identified so far have been ''Dn1-Dn9'' and ''Dnx''. As these genes are marked for selective breeding, it may serve to manage the population of aphids.

Extermination

Biological control

Hopper et al.'s research into biological control is based on the non-pest status of ''D. noxia'' in Eurasia, its area of origin. It is possible that natural enemies in that area limit the abundance of the aphids, therefore preventing them from becoming pests. Based on the selection of natural enemies of ''D. noxia'' in Eurasia, the paper performed a survey of host specificity of different species of parasite from the genus ''Aphelinus''. Although host specificity and range differs from species to species, ''Aphelinus hordei'' has a much narrower range that includes ''D. noxia''. The behavior of females of ''A. hordei'' oviposition orients the species specificity towards ''D. noxia''. Female ''A. hordei'' rarely approaches aphids that are not of the ''D. noxia'' variety. Due to this host specificity, the paper suggests that biological control of ''D. noxia'' may be viable through ''A. hordei'' introduction into the west.

Chemical control

Potassium phosphate was studied as a resistance inducer on wheat plants against ''D. noxia''. It may serve as a method to deal with the population of aphids that have overcome wheat's genetic resistance. The study indicated that potassium phosphate treated plants either a resistant strain or a non-resistant strain both show a decrease in aphid numbers that were feeding. Thus the data suggests treating wheat with potassium phosphate to induce tolerance against ''D. noxia''.

References

External links

Species Profile - Russian Wheat Aphid (''Diuraphis noxia'')
National Invasive Species Information Center,

United States National Agricultural Library The United States National Agricultural Library (NAL) is one of the world's largest agricultural research libraries, and serves as a national library of the United States and as the library of the United States Department of Agriculture. Locate ...

. Lists general information and resources for Russian Wheat Aphid.
Russian Wheat Aphid: An introduced pest of small grains in the High Plains

Kansas State University Kansas State University (KSU, Kansas State, or K-State) is a public university, public Land-grant university, land-grant research university with its main campus in Manhattan, Kansas, United States. It was opened as the state's land-grant coll ...

{{Authority control Macrosiphini Agricultural pest insects Insects described in 1913 Hemiptera of Asia Insect pests of wheat Insect pests of millets