Leafhoppers
Over 380 species of leafhoppers (family Cicadellidae) occur in California. For a list of these species see the California Academy of Sciences insect database (Monarch).
Many different flower, fruit, and vegetable plants and woody ornamentals host leafhoppers. Some species of leafhoppers feed on only several closely related plant species while others feed and move among many different plant species. For example the blue-green leafhopper (Graphocephala atropunctata) feeds on more than 150 species of plants. The Ligurian leafhopper (Eupteryx decemnotata) is a pest of mint, rosemary, sage, and other plants in the mint family (Lamiaceae).
Identification
Leaf stippling (bleached specks) is commonly the most obvious indication that leafhoppers or certain other arthropods that suck plant juices are present. Because discolored spots or overall bleaching of leaves are also caused by lace bugs, plant bugs and other true bugs, spider mites, and thrips, examine the underside of leaves for the arthropods themselves to distinguish the cause of damage.
Adult leafhoppers are relatively long compared with their width, wedge-shaped, and commonly less that 1/4 inch long. Some leafhoppers are called sharpshooters and include larger species such as glassy-winged sharpshooter (Homalodisca vitripennis), the adult of which is about 1/2 inch long. Leafhoppers have one or more long rows of small spines along the entire length of their hind legs, which distinguishes them from some similar-looking types of insects that suck on plant juices. Nymphs are shaped like adults, but their coloration may or may not resemble that of adults.
Leafhoppers are commonly brown, gray, green, or yellow overall or a mottled mix of coloration. Some species are brightly colored, while others blend with the color of their host plant(s). Leafhoppers are active insects that walk rapidly sideways or readily jump when disturbed. Adults and nymphs and the pale cast skins of nymphs are generally found on the underside of leaves or on green shoots.
Life cycle
Leafhoppers develop through 3 life stages: egg, nymph, and adult. Adult female leafhoppers insert their eggs into tender plant tissue, causing tiny pimplelike wounds. The emerging nymphs generally develop through 5 increasingly larger instars before maturing into adults without any pupal stage.
Leafhoppers generally overwinter as eggs that hatch in late winter or spring. Some species, such as the glassy-winged sharpshooter, overwinter as adults on evergreen hosts such as citrus. In locations with mild winters, all stages may be present throughout the year. Most species have two or more generations per year.
Damage
Leafhopper feeding causes leaves to develop pale specks. Leaves and shoot tips fed upon by an abundance of leafhoppers may turn yellow then brown and curl and die. Leafhoppers also excrete honeydew on which blackish sooty mold grows. This can foul foliage, fruit, and surfaces underneath infested plants. As nymphs molt into the next (larger) instar, they leave whitish cast skins on the underside of foliage. Certain leafhoppers such as glassy-winged sharpshooter (Homalodisca vitripennis) and some other species have an excretion that dries to leave a gray or whitish residue on surfaces.
Some leafhopper species transmit plant pathogens that cause plant disease. For example, glassy-winged sharpshooter and various other leafhoppers and sharpshooters vector the plant-pathogenic bacterium Xylella fastidiosa. This bacterium can cause lethal diseases in plant hosts, including almond leaf scorch, oleander leaf scorch, Pierce’s disease of grape, and other diseases that vary by the host plant and strain of X. fastidiosa.
Aster yellows is a phytoplasma disease spread by the aster leafhopper (Macrosteles fascifrons) and certain other leafhoppers. Disease symptoms include yellowing and dwarfing of plants, distorted foliage, and the abnormal production of shoots. In California, aster yellows can damage carrots, celery, lettuce, potatoes, other vegetables, and numerous herbaceous ornamentals.
Curly top virus, spread by the beet leafhopper (Circulifer tenellus), damages many vegetables, including beans, beets, melons, potatoes, peppers, and tomatoes. Infected hosts develop crinkled, dwarfed, and rolled leaves and various other symptoms. Infected hosts have reduced yield and sometimes die prematurely.
Solutions
In most situations, leafhoppers are just an annoyance or curiosity and do not threaten plant survival. Generally, no control of them is needed in gardens and landscapes. Insecticide application in gardens and landscapes generally is not effective for preventing plant diseases vectored by leafhoppers because they can transmit the virus to a new host before the leafhoppers are killed by the insecticide.
Leafhoppers have many natural enemies, including assassin bugs, brown lacewings, damsel bugs, green lacewings, lady beetles, minute pirate bugs, and spiders. Some leafhopper species are attacked by effective parasitoid (parasitic) wasps. For example, Anagrus species are important egg parasitoids of grape-infesting leafhoppers. Unparasitized eggs are translucent and difficult to discern embedded in leaves. But when parasitized by Anagrus, leafhopper eggs turn brown or red unlike their normal translucent color. Glassy-winged sharpshooter eggs are parasitized by various species of introduced Cosmocomoidea (=Gonatocerus) species wasps. When the adult parasitoids emerge, they leave distinctly round holes in the sharpshooter eggs.
For leafhoppers that feed on many different plant species, removing weed hosts and other alternative hosts can reduce the abundance of leafhoppers that migrate to plants that are more desired in gardens and landscapes. Regularly inspect plants for leafhopper nymphs beginning late winter if leafhoppers were a problem the previous growing season. If nymphs are abundant early in the growing season, green shoots and the underside of leaves can be thoroughly sprayed with horticultural oil, insecticidal soap, or neem oil to provide some control.
Adapted from publications linked above and Pests of Landscape Trees and Shrubs: An Integrated Pest Management Guide and Pests of the Garden and Small Farm: A Grower's Guide to Using Less Pesticide, University of California Statewide Integrated Pest Management Program (UC IPM).
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Bleached specks on apple leaves from feeding of rose leafhopper.
Blackish specks of sooty mold growing on grape leafhopper honeydew on grapes.
Adult potato leafhopper.
Cast skins of nymphs of the white apple leafhopper.
Adult (left) and nymph of mountain leafhopper.
Adult (right) and nymph of glassy-winged sharpshooter.
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