English grain aphid,Sitobion avenae.
English grain aphids vary in color from yellow to yellowish-green to orange or reddish-brown. They are among the largest of aphids to be found on wheat, significantly larger than greenbugs, and have long black legs and cornicles with antennae that are slightly longer than half the length of the body. They may be found on wheat right up until maturity and can cause some kernels to shrivel when they feed within heads.
Life History and Behavior
English grain aphids can feed on a wide range of wild grasses and may colonize wheat at any stage in development, usually preferring the upper parts of the plant. They are relatively active aphids, do not tend to form tightly packed colonies like greenbugs, and can disperse rapidly from plant to plant. Winged forms (alatae) develop when the aphids become crowded or their food quality declines. Infestations in wheat are initiated by migrant alatae that come from wild grasses or other cereal crops. Reproduction is asexual throughout much of the year, but populations in temperature regions may produce a sexual generation in the fall with each sexual female (oviparae) laying from 6 to 12 oval, black eggs at the base of a host plant. The eggs are resistant to freezing and hatch into asexual 'stem mothers' in spring. Although the English grain aphid can be a serious pest of cereals in Europe, it is rarely abundant in Kansas wheat and is usually not a cause for concern.
In the fall, S. avenae may feed on the leaves of young wheat plants causing no discernable damage, but it is at this time that they are important as vectors of Barley Yellow Dwarf Virus. Use of seed treatments containing imidacloprid or thiamethoxam may help to reduce the colony establishment of these and other aphid vectors on seedling plants and lower the incidence of BYDV infection. Populations are normally held in check by the same groups of natural enemies suppressing other aphids and chemical treatments are rarely, if ever, justified.
J. P. Michaud
Associate Professor of Entomology
Agricultural Research Center-Hays