G1284 (Revised August 2005) Cereal Aphids G. L. Hein, Extension Entomologist, J. A. Kalisch, Extension Technologist, and J. Thomas, Research Coordinator to living young. A female may produce two to three young Identification and general discussion of the cereal per day under warm conditions, and females may mature in aphid species most commonly found in Nebraska small 7-10 days. This tremendous reproduction potential can result grains, corn, sorghum and millet. in rapid aphid population buildup. Males of some species are seldom if ever seen. Cereal aphids can be a serious threat to several Nebraska Both winged and wingless aphids may be present in the crops. Aphid feeding may cause direct damage to the plant or field. Winged forms are produced when the quality of the host result in transmission of plant diseases. Aphids also may cause plant declines, such as at maturity. Other factors, including damage by injecting toxic salivary secretions during feeding. temperature, photoperiod or seasonality, and population density In Nebraska the most serious cereal aphid problems result also may be involved. The ability of aphids to use flight for from Russian wheat aphid infestations on wheat and barley dispersal is an important factor that contributes to the status and greenbug infestations on sorghum and to a lesser extent of these insects as pests. on wheat. Growers must monitor their crops for these aphids. Greenbug, Schizaphis graminum (Rondani) Several other cereal aphid species also may be present, but they seldom cause significant damage. Accurate aphid identi- The greenbug is a light green aphid with a dark green fication is necessary to make the best management decisions. stripe down the middle of the back. The tips of the legs and Figure 1 illustrates how to identify the major cereal aphids cornicles and most of the antennae are black. Winged forms of found in Nebraska. the greenbug are darker than the wingless forms. Greenbugs Refer to http://ianrpubs.unl.edu/insects, UNL Extension are most often found feeding on the underside of the lower Insect Publications Web site, the http://entomology.unl.edu, leaves of wheat and sorghum; however, they also may be Department of Entomology Web site, or the http://highplain- found in the whorl of seedlings. sipm.org High Plains Integrated Pest Management for more Greenbugs are the most important insect pest of sorghum information on managing cereal aphids. in Nebraska. They seldom overwinter north of southern Kansas, where they can be a major pest of winter wheat, es- Aphid Biology pecially when mild winters permit reproduction and survival. Aphids are small (1/16 to 1/8 inch), soft-bodied insects Infestations in Nebraska originate from winged greenbugs that obtain their nutrition by sucking sap from plants. They blown northward by spring winds. Greenbugs moving into have two cornicles that protrude from the upper surface of the Nebraska early in the spring infest winter wheat and perhaps abdomen near the tail. These “tailpipes” vary in length and other small grains. Later flights from the south, along with may be reduced to mere bumps in some species (e.g., Russian offspring from the earlier flights, begin to infest sorghum from wheat aphid). During feeding, aphids inject salivary secretions late May into June. Damaging levels of greenbugs usually into plant tissues. The salivary secretions of some aphids are occur in late June and July in sorghum. By August popula- toxic and can cause severe tissue damage in the plant. Symp- tions usually begin to decline, often as a result of control by toms of aphid injury include leaf stippling, discoloration or natural enemies. Greenbugs only rarely damage Nebraska striping. In addition, wilting, premature browning and death wheat in the spring, but may occasionally develop damaging of the plants may result. populations in the fall. Plant viruses also can be injected into the plants during Unlike some cereal aphids, salivary secretions of the aphid feeding. Barley yellow dwarf virus can be transmitted greenbug are toxic to the plant. This destructive toxin kills to wheat and barley by the bird-cherry/oat aphid, corn leaf plant cells and results in yellow discoloration of the leaves aphid, greenbug, and English grain aphid. The bird-cherry/ with reddish spotting. The reddish discoloration is especially oat aphid, corn leaf aphid and greenbug also transmit maize distinct on susceptible sorghum varieties. Effects of damage dwarf mosaic virus to corn and sorghum in Nebraska. These are loss of stand, reduced vigor, poorly filled heads, light aphid-vectored diseases usually are not serious in Nebraska; test weight and ultimately reduced yields. The first sign of a however, in some years they can be significant. Disease can greenbug infestation is a circular, yellowish spot in the field. be transmitted whenever a few aphids move in or out of the The center plants in these spots have the highest infestations field rapidly, making their presence difficult to detect. and are the most severely damaged. The primary means of reproduction for the aphid spe- Greenbug management in sorghum relies on the use cies discussed here is asexual (parthenogenesis), with eggs of resistant varieties, conservation of natural enemies and hatching inside the female aphid and the female giving birth timely insecticide applications. Biotypes that have overcome varietal resistance in sorghum are common. In addition, some Cornicles much reduced, cone-shaped, not pigmented Tip of abdomen with Tip of abdomen with single “tail” double “tail” Key to (only cauda present) (extra tail above cauda) Common Aphids in Nebraska Cereal Crops Western Wheat Aphid Russian Wheat Aphid (Diuraphis tritici) (Diuraphis noxia) Aphid Anatomy THORAX Antennae HEAD Wingless Aphids: Body Wingless Aphids: Body light Front Wing light green, spindle shaped green, spindle shaped; all of and often heavily powdered; legs dusky; cornicles light legs, cauda and tips of anten- green, reduced and cone- nae disky; cornicles light shaped; antennae very short green reduced and cone- and dark at tips; projection shaped; antennae very short. above cauda. Cauda Median Vein Cornicle ABDOMEN Winged Aphids: Body dark- er green than wingless form; all of legs and tips of anten- Artwork and slide images, except for Western Wheat Aphid, by Jim Kalisch, nae dark; median vein in front UNL Extension Technologist, Entomology. wings two-forked. Cornicles quite apparent, cylindrical, pigmented. Only tips of cornicles dark Cornicles completely dark Reddish-orange Without reddish-orange Cornicles short and broad; Cornicles long spot on back spot, but with dark green bases of cornicles and narrow around base of cornicles stripe on pale green back often dusky Bird Cherry-oat Aphid Greenbug Corn Leaf Aphid English Grain Aphid (Rhopalosiphum padi) (Schizaphis graminum) (Rhopalosiphum maidis) (Sitobion avenae) Wingless Aphids: Body Wingless Aphids: Body light Wingless Aphids: Body Wingless Aphids: Body olive-green and broadly oval green to pale yellow-green green with bluish tinge; bright green, large and in form with reddish-orange with darker green stripe down head region, legs, cauda, and broadly spindle-shaped, often patches around bases of middle of back; tips of legs, antennae dusky; cornicles shiny; legs, antennae and cornicles; tips of leg seg- tips of cornicles and most of black and dusky at bases; cornicles long; leg segments ments, tips of cornicles and antennae black. antennae and cornicles short. black toward ends; antennae antennae dusky to black. and cornicles completely black. Winged Aphids: Body dark Winged Aphids: Body green Winged Aphids: Body Winged Aphids: Body green green and black; legs dusky and olive-tan with darker dark green and black; legs, with head thorax, antennae, with tips of segments black, green stripe down middle of cornicles, cauda and anten- cauda, cornicles and legs antennae black; median vein back; tips of legs and cor- nae black; antennae short; black; cornicles and antennae in front wings two-forked. nicles black; antennae mostly median vein in front wings long; median vein in front black; median vein in wings two-forked. wings two-forked. one-forked. greenbug populations also have been found to be resistant spring barley as early as possible and maintaining a healthy to certain organophosphate insecticides. These factors have crop will help minimize the risks from the Russian wheat complicated greenbug management. Scouting to detect the aphid. Monitoring aphid populations in the fall and spring presence of these insects and adherence to thresholds is es- and following treatment guidelines are necessary to minimize sential to management. the risk of serious losses. Russian Wheat Aphid, Diuraphis noxia (Mordw.) Corn Leaf Aphid, Rhopalosiphum maidis (Fitch) The Russian wheat aphid is a small aphid with a greenish, The wingless form of the corn leaf aphid is bluish green spindle-shaped body and short antennae. Its cornicles are very with black legs, antennae and cornicles. The winged forms short, and when viewed from the side, it has a double-tailed have a darker body and appear nearly black. The corn leaf appearance because of a projection arising above the cauda. aphid can be found on corn, sorghum, wheat and barley in Damage from the Russian wheat aphid ranges from yellow Nebraska. It is not considered an important pest on any of these or whitish streaking to purpling of the damaged leaves. The crops. Its spring movement to the north seems to lag behind aphid feeds within the whorl of the upper leaves, causing both the greenbug and the English grain aphid. It can be found the leaf to remain tightly rolled. Subsequent leaves may be on wheat late in the spring, and it moves to corn and sorghum trapped by these tightly rolled leaves. As the plant grows, after wheat heading. It generally feeds in the whorl of the Russian wheat aphids continue to move to the whorl and plant, and numbers decline after heading or tassel emergence.