Wheat Insects
Bird Cherry-Oat Aphid, Rhopalosiphum padi (Hemiptera: Sternorryncha: Aphididae)
Wingless adult and nymphs. Photo Credit: G.W. Bishop and S.E. Halbert.
Identification The bird cherry-oat aphid is one of the largest aphids to be found on wheat in Kansas and varies in color depending on the ambient temperature and its stage of growth. Nymphs are usually pale yellowish-green, darkening as they mature to a deep olive green in the adult stage. Normally, a dark brown patch is visible across the posterior portion of the abdomen spanning both cornicles, although it can be difficult to see on the darkest of specimens. Under very warm conditions, adults may be much paler in color, but the cornicles and terminal portions of the antennae are always black. When large colonies persist on wheat plants past the boot stage they can cause the flag leaf to twist into a corkscrew shape that can trap the awns, resulting in 'fish-hooked' heads.
Life History and Behavior Rhopalosiphum padi is a host-alternating aphid – it normally exploits gramimaceous plants (secondary hosts) in summer and returns it its primary woody host (cherry) to complete a sexual generation in the fall. Sexual females (oviparae) lay overwintering eggs on the twigs of cherry and these hatch into first-generation parthenogenetic females (fundrices) in the spring. By the time the daughters of these fundrices mature, the flush of new growth on the cherry trees hardens and is no longer a suitable food source, so virtually all develop into winged forms (alatae) that disperse to colonize suitable graminaceous plants such as wheat, oats or barley. Although R. padi has been recorded from several hundred grasses, species that utilize the C4 metabolic pathway such as corn and sorghum are generally unsuitable as food. It is important to recognize that, in many R. padi populations, the sexual generation (holocycle) is not obligatory. When the climate is sufficiently warm, asexual (anholocyclic) reproduction can continue year-round on graminaceous plants. Anholocyclic populations of R. padi occur in Oklahoma and possibly in southern Kansas and are likely responsible for the migrants that colonize more northern wheat fields very early in spring, often while snow is still on the ground. The advent of warmer winters in Europe has resulted in year-round asexual reproduction by R. padi as far north as Poland where it has been recently linked to increased rates of disease transmission in spring-sown cereals. The bird cherry-oat aphid can be considered a cryptic pest of wheat. Although its feeding causes no chlorosis or other visible damage to wheat plants, heavy infestations can reduce grain quality, affect protein content and test weight, and even reduce protein assimilation by grazing cattle. However, its greatest economic impact on grain production results from its role as a key vector of plant viruses, especially Barley Yellow Dwarf Virus (BYDV). Virus infections are more damaging when they occur in early growth stages of the wheat plant and R. padi is well able to accomplish this. Although the hot summer weather in Kansas is usually effective in decimating aphid populations, R. padi can temporarily avoid extremes of temperature by descending to feed on the lowest parts of the stalk, at or below ground level. It is also able to feed actively in weather too cold for other aphids such as greenbug, enabling it to effectively colonize seedling wheat quite late into the fall.
Management The bird cherry-oat aphid is usually held below economic injury levels by the same groups of natural enemies that provide effective biological control of other cereal aphids in Kansas wheat: lady beetles, lacewings, hover flies, and parasitic wasps. However, conditions that favor outbreaks of greenbug or Russian wheat aphid (for example, an abrupt shift back to cold temperatures after a warm spell in spring) also benefit R. padi and it will often be found forming mixed colonies with these aphids when they are abundant. In such cases, decisions to apply pesticides should be driven by the numbers of those direct-damaging species and materials applied to control them should be equally effective against R. padi. If R. padiis present alone, count the number of aphids present on each of a series of 25 - 50 randomly selected tillers across a zig-zag transect of the field. Treatment with an insecticide broadly labeled for aphid control on wheat can be considered if an average of 50 or more aphids per tiller are present from boot stage up until heading. However, treatment with contact insecticides will not reduce the incidence of virus transmission. Some studies have shown that seed treatments containing imidacloprid (Dyna-Shield Imidacloprid, Gaucho, or Gaucho XT) or thiamethoxam (Cruiser) reduce BYDV infection by suppressing aphid colony establishment during the seedling stage.
J.P. Michaud,
Associate Professor of Entomology
Agricultural Research Center-Hays
May 2008.
This publication was prepared to help producers manage insect populations with the best available methods proven practical under Kansas conditions. Pesticide label directions and restrictions are subject to change, and some may have changed since this publication was written. Kansas State University entomologists assume no responsibility for product performance, personal injury, property damage, or other types of loss resulting from the handling or use of the pesticides listed. Remember, it is illegal to use a pesticide in a manner that is inconsistent with the label. The user bears responsibility for correct use. Always read and follow label directions carefully.
Additional Information can be found in the KSRE publication MF2823: Bird Cherry-Oat Aphid.
Please refer to the most recent version of the Wheat Insect Management Guide for control options.