Common Name: Greenbug, aphid
Scientific Name: Varies
Description: Mature female greenbugs are winged or wingless, pear-shaped, about 1/16-inch long, pale green, and marked with a darker green stripe down the middle of the back and black tips on the legs and the two appendages (cornicles) on the back of the abdomen.
A number of other aphid species are pests of small grains, corn and sorghum. The yellow sugarcane aphid, Sipha flava (Forbes), is most injurious to sorghum along the Texas coast but is also found on small grains, Johnsongrass and Dallisgrass. These aphids feed on the underside of the lower leaves, causing injured leaves to turn purple and eventually die from the injection of toxic saliva.
The wingless form of the yellow sugarcane aphid is bright lemon yellow with rows of bumps (tubercles) along the abdomen from which hairs (setae), has short cornicles (not longer than wide), and five segmented antennae.
Introduced in 1986, the Russian wheat aphid, Diuraphis noxia (Mordvilko) pest injures wheat, barley, rye, triticale and oats in the Texas panhandle and also infests some wild grasses. Injured leaves develop curling, white to yellow streaking in warm weather or purple discoloration in cool weather and may die as a reaction to an injected toxin. The wingless Russian wheat aphid is darker green, also has short cornicles, but has six-segmented antennae and a conspicuous elongated structure (caudal process) on the back end of the body that gives it a “double tail” appearance when viewed from the side.
The corn leaf aphid, Rhopalosiphum maidis (Fitch), is common throughout Texas, especially in the leaf whorls of corn and sorghum, and to a lesser extent on small grains. It is not generally considered injurious because it does not inject a toxin when feeding and attracts natural enemies. The wingless form is bluish-green with black
appendages and base of cornicles, which are longer than wide. The English grain aphid, Sitobion avenae (Fabricius), on wheat, barley, rye or oats and the oat-bird-cherry aphid, Rhopalosiphum padi Linnaeus, on small grains in western and northwestern Texas are also rarely serious pests because they do not inject a toxic salivary secretion. The wingless English grain aphid is similar to the corn leaf aphid, but is grass-green (occasionally yellow or pink) with a brown head and has longer black legs and cornicles. The wingless oat-bird-cherry aphid has an olive body with a reddish-orange spot on the back at the base of the cornicles and tips of antennae, legs and antennae black.
The yellow sugarcane aphid, Silpha flava (Forbes) (Homoptera: Aphididiae) is a pest of sorghum. All wingless stages are lemon-yellow, with the body bearing small spines and marked with two rows of small dark spots down the back. When feeding on leaves of seedling sorghum, these aphids inject a toxin which causes infested leaves to turn purplish. Injury to more mature leaves causes yellowish discoloration and stunting. Heavily infested plants in the pre-boot stage may die. Alternate host plants include Johnsongrass and dallisgrass.
Life Cycle: Gradual metamorphosis; parthenogenic. Mature females produce live young nymphs without mating. These nymphs develop into adults within 6 to 30 days, depending on temperature, and also produce live young at a rate of 2 to 3 per day over a 20 to 30 day period. Populations can increase quickly, about 5- to 6-fold per week under normal conditions. Many generations occur per year and they can be found year-round in the Texas wherever host plants occur. Infestations spread by winged forms flying and being blown many miles by the wind.
Habitat and Food Source(s): Greenbugs are found primarily on wheat during the winter months and sorghum during the spring and summer, but they also occur on Johnsongrass, other wild grasses and occasionally on oats. Adults and nymphs occur on the underside of leaves, particularly on the lower, older leaves of host plants. They damage plants in three ways: 1) they remove sap, stressing plants by removing water and nutrients; 2) they inject a toxic salivary secretion that causes cells, leading to a yellowing or reddening discoloration and eventually death on infested tissues; and 3) they can transmit plant disease such as the barley yellow dwarf virus in small grains and maize dwarf mosaic virus in sorghum. They infest plants of all growth stages and can kill young plants, reducing plant stand. Heavily injured older plants have stunted growth, delayed growth, reduced kernel size and quality. Several biotypes have evolved that have overcome plant resistance, tolerate temperature extremes and infest new host plants.
Pest Status: Pests of several cultivated and wild grasses; in wheat and sorghum crops, they can injure plants, transmit plant diseases and reduce yields; medically harmless.
Literature: Daniels 1981; Halbert et al.1988. Hoelscher et al. 1987.