Endria inimica (Say 1830b: 305 )

Description & Identification

Small, linear species. Length of male 3.70—4.20 mm., female 4.20—4.40 mm. (Nielson, 1968)General color yellowish tan with numerous brown or black markings on body. Crown yellow with two spots near anterior margin and two small spots near posterior margin; pronotum with two spots near anterior margin; elytra tan with cells bordered with brown markings, spots and markings vary in size and number among specimens.(Nielson, 1968)Pygofer in lateral aspect nearly twice as long as wide, caudal margin slightly concave; aedeagus fused to connective, sinuate in lateral aspect, tubelike, with small lateral tooth near middle of shaft on dorsal margin, shaft with large sagittal groove and apex notched in dorsal aspect; style in dorsal aspect simple, apex narrow; female seventh sternum in ventral aspect with median spatulate process on caudal margin, margin sinuate on either side of spatulate process. (Nielson, 1968)This is the only species of the genus Endria that is a vector (Nielson 1968)

Biology & Ecology

The biology of this species is well known. Host plants and life-history studies were first reported by Osborn and Ball in 1897 (606) and Osborn between 1893 and 1939 (594, 595, 599, 605). The species was most common on bluegrass, which is considered a favorite food plant. It was also found on timothy, wheat, oats, corn, millet, rye, clover, alfalfa, and many wild grasses in the plains region. In 1954 Wilbur (860) found that native grasses of the true prairie were unsuitable hosts and that -the species preferred introduced species of plants. Of 31,000 specimens collected during a 7-year period, the upland native grass supported 3.6 percent of the insect population, Kentucky bluegrass and weed-grass pasture 30.2 percent, and smooth brome and orchardgrass 66.2 percent.Life-history observations on bluegrass in Iowa showed that eggs were deposited in the leaf or stem beneath the epidermis. The insect overwintered in the egg stage and hatched in the last part of April or early May. Adults appeared in late June and early July, laying eggs that hatched in a few days. Two generations a year occurred in the field. (Nielson, 1968)

Worldwide Distribution

It is widely distributed in the United States and Canada. In 1949, Oman (588) recorded it from the Central, Northeastern, and Southeastern United States. it is common and widespread in the southern parts of British Columbia, Alberta, Saskatchewan, Manitoba, Ontario, and Quebec (Beirne 1956 [58]). (Nielson, 1968)

Vector Status

Economic Crops

This species is a vector of striate mosaic virus of wheat and other grains in the United States and Canada and the western strain of North American aster yellows virus of wheat and barley in eastern Canada, Slykhuis in 1951 (733) was first to suggest this species as a vector of striate mosaic based on preliminary tests. Later in 1934 and 1936 he (734, 736) confirmed transmission and proved that inimnica was the vector among other species of leaf-hoppers tested. Transmission was effected to several varieties of wheat as well as barley and oats. Some naturally infected grasses were used as inoculum in transmitting the virus to wheat. After an acquisition feeding period of 16 hours, the insect transmitted the virus in 10 to 14 days. About 34 percent of the initially fed leafhoppers transmitted the virus whereas 65 percent of the surviving population were infective after a latent period of 31 days. Virus retention was as long as 76 days, and some leafhoppers transmitted once whereas others did so regularly. The incubation period of the virus in plants varied from 15 to 45 days. Both nymphs and adults acquired the virus and transmitted it as nymphs and adults.In 1960, Timian (789) reported results of transmission of the virus to durum wheat in North Dakota. Mechanical transmission of the virus to noninfective leafhoppers was accomplished by Lee in 1963 (444). Nineteen days after infection about 80 percent of the leafhoppers were infective and most of them transmitted the virus until they died.In 1964 Slykhuis and Sherwood (737) in their studies on the relationship of temperature to transmission found that the leafhopper acquired the virus in 15 minutes or more on diseased wheat at 100 to 33° C. The percent of test plants infected increased from12.5 at 10° to 81.4 at 33°. Temperature was not critical for virus acquisition, but transmission and disease development were favored by high temperature.Chiykowski in 1963 (138) transmitted the western strain of North American aster yellows virus from infected celery to barley and wheat. After an S-hour acquisition feeding period 12.4 percent of the leafhoppers were infective. Longer periods up to 24 hours produced 30-percent infective populations. The minimum and maximum latent periods of the Virus in the vector were 18 to 25 and 73 to 81 days, respectively.(Nielson 1968)This species is an important vector in the natural spread of wheat striate mosaic virus. Its importance in the spread of aster yellows virus to wheat and barley has not been fully assessed, but it has considerable potential if it should prove to be a migratory species.(Nielson 1968)

Plant Diseases