|Scientific Name||Metopolophium dirhodum (Walker, 1849)|
|Common Names||English: Rose-grain aphid; German: Bleiche Getreidelaus; Spanish: Pulgon de la cebada; French: Puceron des céréales et du rosier|
|Description||This aphid has a spindle-shaped body with rather long siphunculi. It is green, with a noticeably lighter stripe along the back. The apterae are up to 3 mm (0.118 inch) in length, the oviparous females less than 2 mm (0.078 inch). The length of the antennae is about ¾ that of the whole body.|
Like all aphids, M. dirhodum feeds on plant sap, which it obtains by puncturing phloem vessels. Its saliva does not contain any substances that are toxic to the plant, but the drain of nutrients and water can lead to yield losses if the aphid occurs in large numbers. Plants that are already under water stress may start to yellow and become stunted. Depending on the course of an infestation, both the number and size of the grains may be reduced; infestations during the period between tillering and the end of flowering are particularly harmful.
Apart from the direct damage it causes, M. dirhodum is also a vector of several plant viruses, most importantly barley yellow dwarf virus, but maize mosaic virus and potato viruses can also be damaging.
The honeydew it produces promotes growth of saprophytic fungi that are detrimental to plant health.
Like most aphids, M. dirhodum usually undergoes an alternation of generations and hosts. The summer generation („virginoparae“), which lives on the secondary host, is parthenogenetic, and consists solely of females. Only in the autumn do morphs („sexuales“) of both sexes appear, mate and produce eggs, which are laid on the primary host (Rosa spp.). The colony founders („fundatrices“) hatch in the spring, and adults of the subsequent second or third generations migrate to the summer host (Poaceae). However, in regions with mild, temperate climates, this aphid can be anholocyclic, i.e. without a sexual generation and with aphids overwintering on the secondary host as well. Mild autumns and winters, an early rise in temperatures in spring, and warm, dry weather in summer are conditions favourable for rapid population increase. Peak densities tend to more or less coincide with the milky stage of cereal development. However, high temperatures (above ~30°C, 86°F) are detrimental to this aphid, and strong winds or heavy rain can also cause considerable mortality. The preferred feeding sites are the undersides of leaves, and less often, the ears. As the plant grows, the aphid colonies climb from aging to younger parts.
When a host becomes overcrowded, winged morphs („alatae“) develop and then spread to other plants. They may be carried over large distances by wind.
M. dirhodum is of palaearctic origin, but is nowadays found in almost all grain-producing regions of the world. The abundance of this aphid can vary greatly between years and localities according to climatic conditions and the influence of natural antagonists. Although it seldom causes dramatic losses, the yield reductions it causes can result in significant economic losses.
Integrated Crop Management
Crops well-supplied with water will be much better able to tolerate aphid infestations. Active populations of natural enemies play an important role in the control of this pest. Avoid excessive applications of nitrogen fertilizer, as this increases the suitability of plants as hosts for the aphid. Late-sown cereals may evade the peak of aphid population densities.
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