Battle of the Bugs

The glassy-winged sharpshooter, a half-inch-long insect from northern Mexico and the southern United States, is spreading a bacterial infection lethal to grapevines in California. Three tiny wasps may be the answer to saving the $2.8 billion wine, grape, and raisin industries.

As spring blooms and adult glassy-winged sharpshooters (Homalodisca coagulata) come out of winter dormancy, agricultural taskforce specialists and scientists at UC Berkeley, Davis, and Riverside are working to stop this nonnative invader's spread northward.

Map credit: California Department of Food and Agriculture

Although native disease-carrying sharpshooters have occasionally infested California vineyards for a century, they attack only new growth, and annual pruning removes the disease. The faster-spreading nonnative glassy-winged sharpshooter is a dangerous threat, stimulating 50 different research projects to protect vines.

Glassy-winged sharpshooter is significantly larger than the California native blue-green sharpshooter (Draeculacephala minerva) credit: UC Pierce's Disease Research and Emergency Response Task Force

Homalodisca coagulata, a heavy drinker attacking the wine industry, consumes so many times its weight in plant sap that it is the equivalent of a 150-pound person drinking 4,300 gallons daily. Credit: UC Davis

When a sharpshooter pierces the woody stem of a vine with its strong mouthparts, it transmits a bacteria into the plant that causes a fatal disease known as Pierce's Disease. The deadly bacteria, Xylella fastidiosa, attacks the cells responsible for the flow of water and nutrients throughout the plant, the leaves are scorched, and the plant dies.

To stop the spread of this dangerous pest, scientists are using wasps smaller than a grain of rice. One major trial involves Mexican stingless wasps (Gonatocerus triguttatus), a natural enemy that parasitizes sharpshooters' eggs in the spring. Two California parasitic wasps (Gonatocerus morrelli and Gonatocerus ashmeadi) are more effective controls in the fall. Though all these wasps don't have naturally large populations, armies of them are now being raised to combat the sharpshooter.

Grapevine with evidence of Pierce's disease on leaves and stem. Credit: UC Berkeley

The Xylella fasticiosa bacterium blocks the grapevines' vascular tissue. Credit: UC Pierce's Disease Research and Emergency Response Task Force