No abstract

Hordeum vulgare. A few days before hatching, the packets of eggs were dissected from the leaves, and placed on a strip of moist filter paper, one end extending out of the mouth of a phial and the other end submerged in water. The bottom of the phial was embedded in soil in a 6-inch flower pot in contact with barley plants. The nymphs upon hatching crawled on the barley plants, and some completed the nymphal stages, but only a low population of adults was reared. The method of obtaining noninfective blue-green sharpshooters, N eokolla circellata, was similar to that first described by Stahl and Carsner (1918) for the beet leafhopper, and later illustrated by Severin (1921). Other species of leafhoppers collected in the field were transferred in lots of 20 adults to healthy grapevines or alfalfa plants, to test natural infectivity before using them in vector-efficiency tests in virus transmission. The vines and alfalfa plants served as control plants. The insects were rarely naturally infective. This confirms the results of Hewitt, Houston, Frazier, and Freitag (1946) with Carneocephala fulgida and H elochara delta. The grapevines used were the varieties Emperor, Ribier, Palomino, and Thompson Seedless (Vitis vin•ifera) propagated from indexed cuttings, and wild grapevine (V. californica) grown from seeds. Vines grown from cuttings were used in all tests with multiple lots and also in all single-lot tests except in 1943 and 1944, when seedlings were used. The alfalfa was in all cases the California Common variety of Medicago sativa. Details of methods used for specific aspects of transmission tests are given in appropriate sections.

No abstract

No abstract

even abandoned. Aster plots showing 90 to 95 per cent of yellowed plants are not uncommon throughout the eastern United States." Aster yellows first made its appearance in California during 1925 and in the next three years the disease has spread rapidly through the middle and southern sections of the state. Yellows of flowering plants is already causing some concern to seed and flower growers in certain localities. An investigation was undertaken to determine whether insects, especially leafhoppers, transmitted this disease to celery. Experiments were conducted to determine the relation of the celery disease to aster and lettuce yellows. The relation of yellows to curly top of sugar beets was also investigated. The characteristics, distribution, flights, food plants, and overwintering stage of the six-spotted leafhopper are discussed in this paper. NAl\IE OF THE DISEASE A large number of plant diseases are designated by the term "yellows" some of which belong' to the virus diseases, as does the one under consideration, while others are caused by fungus parasites. Kunkel (5) has experimentally transmitted aster yellows with the sixspotted leafhopper, Cicadula sexnotata (Fall.) to more than seventy species of plants in twenty-eight families. Celery yellows has been proven to be identical with aster yellows and should be classified with this disease. , , Yellows" of celery caused by a species of Fusarium occurs in Michigan, Indiana, Ohio, Pennsylvania, New York, Massachusetts, Connecticut, and New Jersey but has not been reported from California. OCCURRENCE OF YELLOWS IN CALI~-'ORNIA Methods of Introduction into California.-The six-spotted leafhopper, Cicadula sexnotata (Fall.) has been known to occur in California for a long time, but the yellows disease which it transmits is a recent introduction into the state. Yellows disease may have been introduced into California through shipments of diseased perennial flowering' plants from the Middlewest or East, or through cut flowers brought from the Middlewest or East by the traveling public. Successive migrations of infective six-spotted leafhoppers from the Middlewest to California appear to be entirely out of consideration