Symptoms induced by some species of aphids feeding on ferns

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During the past five years, 25 large birds-nest ferns (Asplenium nidus) have been kept in a greenhouse at the University of California, Berkeley. In the spring of 1949 five of these plants developed chlorotic circular and spindle-shaped areas extending laterally from the midrib (plate 1) on the fronds. No aphids were found on any of the plants.

On May 10, 1949, two large birds-nest ferns with dark green streaks on the fronds were found in a greenhouse in San Francisco. One hundred small plants were obtained from the same nursery, and after transplanting in five-inch clay pots, ten plants developed dark green streaks on several of the youngest fronds. No symptoms appeared on the newly developing fronds. Again no aphids were found on birds-nest ferns in greenhouses in San Francisco and San Mateo Counties.

Review of Literature

(Severin, Horn, and Frazier (1945))4 reviewed the literature on plant symptoms induced by the feeding of a leaf hopper, and described certain symptoms, resembling those of curly top and aster yellows, induced by the saliva of Xerophloea vanduzeei Lawson. On sugar beets (Beta vulgaris) the saliva induced cleared veinlets, previously considered a reliable symptom of curly top. On China aster (Callistephus chinensis) it caused cleared venation with yellow veinbanding, stunting of the plants, development of axillary shoots from the bud in the axil of the leaves, and virescence of the flowers, all symptoms being similar to those of aster yellows. The most striking effect produced by the feeding of the leafhoppers was color-breaking in the petals of asters.

In a recent paper, (Severin (1947)) described the symptoms induced by ten species of noninfective leafhoppers, all vectors of the California-aster-yellows virus, on the leaves of healthy China aster, Golden S elf-Blanching celery (Apium graveolens var. dulce), and sugar-beet plants. Nymphs of Idiodonus heidemanni Ball are yellow in color, and each nymph in feeding on an aster leaf causes a yellow discoloration, presumably serving as a protective resemblance.