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Diuraphis apterae are characterized by a slender elongate body, with a membranous dorsum except for cross bands on the posterior abdominal tergites, and intersegmental abdominal sclerites in some species. They are usually wax-dusted. Antennal & median frontal tubercles are low or undeveloped. The antennae are 5 or 6-segmented, 0.3-0.5 times body length with a terminal process that is 1-2 times the base of antennal segment VI. Secondary rhinaria are absent in the aptera. The rostrum reaches to the middle coxae, or between fore and middle coxae. The apical rostral segment is 0.5-1.0 times as long as the second hind tarsal segment. Marginal tubercles are occasionally present on the prothorax and on abdominal segments II-VI, most frequently on V. An unpaired spinal supracaudal process is present in subgenus Diuraphis, but absent in subgenus Holcaphis. Dorsal setae are occasionally spatulate. The first tarsal segments in adults have 3-3-2 setae (fore-mid-hind). The siphunculi are inconspicuous, placed on the posterior part of tergite VI, as long as their width or shorter, and without an apical flange. The cauda is tongue-shaped with 4-9 hairs.
Diuraphis alatae have more or less distinct marginal sclerites. They have a few secondary rhinaria on antennal segment III, and sometimes also on IV.
There are 10 species of Diuraphis worldwide, in two subgenera, - Holcaphis and Diuraphis sstr.. They do not host alternate, but live on the leaves of various cultivated and wild grasses (Poaceae). They usually roll or otherwise distort the grass leaves, often giving a characteristic discoloration to the leaves. Diuraphis aphids are holocyclic, but often with anholocyclic populations in the warmer parts of their range. Some species, especially Diuraphis noxia, can be serious pests of cultivated cereals. Diuraphis aphids are not attended by ants. They are found across the Palaearctic and Nearctic zones.
Diuraphis frequens (Couch grass aphid) Europe, Asia and North America
Adult apterae of Diuraphis frequens (see first picture below) are very elongate, green, powdered with grey wax, with the head darker, and blackish appendages. Their antennae are only about 0.3 as long as the body, with the terminal process 1.05-1.5 times as long as the base of antennal segment VI (cf. Diuraphis holci, which has the terminal process 1.3-1.9 times its base). The rostrum is short, nearly reaching the second pair of coxae, with the apical rostral segment (RIV+V) 0.5-0.75 times the second hind tarsal segment (HTII) (cf. Diuraphis tritici, which has RIV+V 0.9-1.15 times HTII). The abdomen has sclerotic stigmatic plates and sclerotic crossbars on tergites VII and VIII. There is no supracaudal process on abdominal tergite VIII, and usually no marginal tubercles on abdominal tergites II-VI (cf. Diuraphis noxia, Diuraphis mexicana & Diuraphis muehlei, which have a supracaudal process on tergite VIII, and marginal tubercles on at least tergites III-V). The siphunculi are very short dark cylinders about 0.25 times the caudal length, with apertures directed backwards. The siphunculi are placed equidistantly from the spiracles on abdominal segments VI and VII (cf. Diuraphis holci, which has the siphunculi placed closer to spiracle on segment VI than to that on VII). The cauda is dark and sclerotic with 5 or 6 hairs. The body length of an adult Diuraphis frequens aptera is 1.3-2.1 mm.
Images copyright Frank Peairs, Colorado State University, Bugwood.org under a Creative Commons licence.
The alate Diuraphis frequens has a green body. The antennae are about 0.5 times the body length, and bear 4-8 secondary rhinaria on segment III, and 0-2 rhinaria on segment IV. The legs are much longer than in apterous viviparous females, but other characteristics are similar.
The most common host of Diuraphis frequens is couch grass (Elymus repens). It has also been recorded from other grass genera such as cockspur grass (Echinochloa), barley (Hordeum), rye grass (Lolium) and wheat (Triticum). After hatching the fundatrices penetrate between unrolling leaves of couch grass and stop their growth, which results in a bunch of rolled leaves at the apex of the plant. Colonies of Diuraphis frequens live in the rolled leaves, with alatae appearing in the third generation. In October sexuales appear with both the oviparae and males being apterous. Diuraphis frequens is widespread, and sometimes common, in Europe, Asia and North America.
Diuraphis mexicana (Brome grass aphid) Mexico, Western USA, Western Canada
Adult apterae of Diuraphis mexicana (see first picture below) are pale yellow-brown to pale green with a pale brown head and appendages, and are wax-powdered. Their antennae are shorter than the body, with the terminal process 0.9-1.25 times the base of antennal segment VI (cf. Diuraphis muehlei, which has the terminal process 1.2-1.65 times the base, or down to 1.0 in summer dwarfs). The length of hairs on antennal segment III is approximately 0.5 times the diameter of its base (cf. Diuraphis calamagrostis in Europe, which has these hairs only slightly less than the diameter of the base). The rostrum extends to the middle coxae with the apical rostral segment shorter than the second hind tarsal segment (HTII). Abdominal tergites III-V (sometimes also II and VI) have small marginal tubercles (cf. Diuraphis frequens, which has marginal tubercles absent). Abdominal tergite VIII has a short, broadly triangular supracaudal process (cf. Diuraphis noxia & Diuraphis muehlei, which both have a longer finger-like process on tergite VIII). The siphunculi are short, without an apical flange (cf. Diuraphis mexicana Diuraphis noxia, which has an apical flange on the siphunculi). The cauda is elongate, triangular with a pointed apex, and usually with 4 lateral hairs. The body length of adult Diuraphis mexicana apterae is 1.4-2.0 mm.
Images copyright Frank Peairs, Colorado State University, Bugwood.org under a creative commons licence.
The alate Diuraphis mexicana has antennae shorter than the body, with 4-7 secondary rhinaria distributed in a straight row on antennal segment III, 0-2 on segment IV, and none on segment V. The wings have the veins fuscous bordered. The abdominal dorsum has no sclerotized patches or bands.
Colonies of Diuraphis mexicana feed on open or rolled leaves of brome grass (Bromus) species, especially mountain brome (Bromus marginatus), cheat grass (Bromus tectorum) and California brome (Bromus carinatus), as well as on orchard grass (Dactylis glomerata). Aphid colonies may occur on open leaves or within rolled leaves, with feeding damage expressed as yellow streaking on light green leaves. In Mexico and California the species is mainly anholocyclic, but it is thought to be monoecious holocyclic further north (see picture of egg above). Diuraphis mexicana is found in Mexico, Western USA and British Columbia, Canada.
Diuraphis noxia (Russian wheat aphid) Near cosmopolitan, but not Western Europe
Adult apterae of Diuraphis noxia (see first picture below) are pale yellow green, or grey green, lightly coated with a waxy white powder. The antennae are shorter than the body, with a terminal process 1.6-2.3 times longer than base of antennal segment VI (cf. Diuraphis tritici and Diuraphis frequens, which both have the terminal process less than 1.5 times longer than the base of that segment). The rostrum extends to the middle pair of coxae. The apical rostral segment (RIV+V) is approximately twice as long as wide at its base, lacks accessory hairs, and is shorter than the second hind tarsal segment (HTII). Prothoracic and abdominal marginal tubercles are present. The dorsum is spiculose with sclerites on segments VI-VIII. There is a supracaudal process on segment VIII which is finger-like, and 0.5-0.6 times as long as the cauda (cf. Diuraphis muehlei on Phleum, whose supracaudal process is 0.25-0.33 times the caudal length; and cf. Diuraphis mexicana, which has a small poorly-defined triangular supracaudal process). Their siphunculi are pale and very short, as wide as they are long and have an apical flange. The cauda is elongate, triangular, with 4-6 lateral hairs and 0-2 preapical hairs. The adult Diuraphis noxia aptera body length is 1.4-2.3 mm.
Images above, copyright Jesse Rorabaugh, no rights reserved.
The alate Diuraphis noxia (see second picture above) has a dark head, a brownish-green thorax with dark markings, and a pale green abdomen with little or no wax powdering. The antenna are shorter than the body, with 3-7 secondary rhinaria in a straight row on segment III. There are 1-3 secondary rhinaria on segment IV, and none on V. The wing veins have fuscous highlighting. The abdomen has marginal abdominal tubercles as well as marginal sclerites, and median sclerites on segments VII-VIII. The supracaudal process on segment VIII is reduced compared to the aptera.
Diuraphis noxia feeds on a wide range of grasses and cereals (such as Agropyron, Bromus, Elymus, Hordeum, Triticum), but not usually on maize (Zea). It is very damaging to wheat and barley, as infested leaves are rolled into tubes and desiccated, and infested ears become bent. The Russian wheat aphid is monoecious holocyclic with apterous males in colder parts of its range, but seems mainly or entirely anholocyclic in warmer regions. It is of palaearctic origin, and now very widespread in southern Europe, Middle East, Central Asia, Africa, South & North America and Australia, but apparently not in western or northern Europe.
Diuraphis tritici (Western wheatgrass aphid) East Asia, Western USA, Peru
Adult apterae of Diuraphis tritici (see picture below) are pale yellowish-green, but that colour is obscured by a rather dense covering of fine white wax powder. Their siphunculi, cauda and legs are dusky. Their antennae are much shorter than the body. The rostrum extends to or past the second pair of coxae (cf. Diuraphis frequens, which has a short rostrum, not reaching the second pair of coxae). The apical rostral segment (RIV+V) is approximately 3 times as long as wide at base, with 2 accessory hairs; it is 0.9-1.15 times as long as the second hind tarsal segment (HTII) (cf. Diuraphis frequens, which has a relatively shorter RIV+V at only 0.5-0.75 times HTII). There is no supracaudal process on abdominal tergite VIII, and usually no marginal tubercles on abdominal tergites II-VI (cf. Diuraphis noxia, Diuraphis mexicana & Diuraphis muehlei, which have a supracaudal process on tergite VIII, and marginal tubercles on at least tergites III-V). The siphunculi are short, without an apical flange. The cauda is elongate, triangular with rounded apex, and with 4-6 lateral hairs. The body length of adult Diuraphis tritici apterae is 1.9-2.2 mm.
Note: Although the picture below appears to show that Diuraphis tritici has a denser whiter wax coating than Diuraphis frequens, this may not be a reliable character to distinguish the species. The degree of waxing of aphids tends to be very variable, depending on time since last moult, climate factors, degree of ant attendance and (we expect) predation.
Image copyright Frank Peairs, Colorado State University, Bugwood.org under a creative commons licence.
The alate Diuraphis tritici (not pictured) has a green abdomen. The head, thorax, most of antennae, and the cauda are black. The siphunculi are a little yellowish or brownish. The body is covered with white wax powder. The antennae are shorter than body, with 4-7 secondary rhinaria on segment III, 1-3 on IV and 0-1 on V. The wing veins are conspicuously darkened.
Diuraphis tritici lives in the curled leaves of grasses, especially western wheatgrass (Elymus smithi) and other Elymus species, and also sometimes on wheat (Triticum). Feeding damage is expressed as regular red or yellowish streaking on the green leaves. It is monoecious holocyclic with oviparae and apterous males in October. Diuraphis tritici are not attended by ants. It was first found and described in several western states of the USA, and more recently in Peru. It is also found in East Asia where it is may have originated, although most workers consider it a native American species.