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Russian wheat aphidOn this page: Identification & Distribution Other aphids on the same host Damage & Control
Identification & Distribution
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.
Other aphids on the same host
Diuraphis noxia has been recorded on 4 Triticum species (Triticum aestivum, Triticum durum, Triticum monococcum, Triticum turanicum). Several species of the Triticum genus are grown as 'wheat' - the most common being Triticum aestivum.
Diuraphis noxia has been recorded on 10 Hordeum species (Hordeum brevisubulatum, Hordeum bulbosum, Hordeum comosum, Hordeum distichon, Hordeum jubatum, Hordeum murinum, Hordeum murinum ssp. leporinum, Hordeum roshevitzii, Hordeum secalinum, Hordeum vulgare).
Diuraphis frequens has been recorded on 5 Elymus species (Elymus canadensis, Elymus dahuricus, Elymus elongatus, Elymus hispidus, Elymus repens).
Damage and control
Diuraphis noxia is especially injurious to wheat and barley. It is thought to inject a polypeptide toxin when it feeds that affects the entire plant. Even very small colonies of aphids on plants before flowering cause characteristic white to red/purple streaking and leaf-rolling on wheat and barley leaves (see picture below). These streaks usually extend over most of the long axis of the leaf and are irregularly distributed across the short axis of the leaf.
Image above copyright Phil Sloderbeck, Kansas State University/Bugwood.org under a creative commons licence.
Leaf rolling rangess in severity from simple folding of the leaf along the mid-vein, to one side of the leaf rolled in upon itself, to the whole leaf being tightly rolled around the aphid colony. Large colonies can roll the plant's flag leaf to the point where the tip of the inflorescence becomes trapped, giving it a fish-hook shape. Young plants are stunted and even killed. Plants attacked after flowering show few to no obvious symptoms.
There are various methods of cultural control: Delaying planting beyond the period at the beginning of a season when alate Diuraphis noxia are abundant can reduce initial infestations. Management of crop residues and alternative host-plants also appears promising. The current practice in much of the western USA is to plough-under all crop residues and strictly control non-crop plants with herbicides. Although this does reduce reservoirs for Diuraphis noxia and other pests, it also reduces sources of natural enemies of these pests. Replacement of wild grasses currently used for forage with grasses less suitable for Diuraphis noxia growth may be a better approach. Many natural enemies, including predators, parasitoids and pathogenic fungi, have been recorded attacking Diuraphis noxia, although few show any specificity to the pest. Moreover, the feeding of the aphid within the leaf whorls of cereal plants does limit access of natural enemies to the aphid colonies. For more information on symptoms and methods of cultural and biological control of Diuraphis noxia see CABI.
Control of Russian wheat aphid worldwide has mainly been carried out using foliar insecticides. The main ones recommended are organophosphates, synthetic pyrethroids and pirimicarb (a carbamate). Insecticide seed treatments have some advantage over foliar applications, and can be very effective against early aphid invasions. Seed treatments were widely used in Australia to counteract the relatively recent establishment of Diuraphis noxia in that country in 2016 (see Ward et al., 2020).