Anecdotal evidence from growers that spiders suppress vineyard pests is being put to the test by Kearney Agricultural Center scientists Kent Daane and Michael Costello, who are looking for direct proof from the spiders' stomachs.

“We don't know all the types of prey spiders feed on in the field,” said Costello, a UC postdoctoral researcher. “And for this reason we don't know what role they play in biological control of insect pests.”

To discern which spiders eat leafhoppers, Costello and Daane, a UC Berkeley biological control specialist, are trying serological gut analysis. But first they must isolate an antibody that can be used to detect the presence of leafhoppers in spider stomachs.

“Through this method, we have the potential to quickly screen dozens of predators, not just spiders, to help determine which is best for control of leafhoppers,” Daane said.

Variegated leafhopper is a common vineyard pest which damages grape leaves and flies into pickers' eyes, noses and ears. Most growers spray insecticides to control leafhoppers, but by identifying spiders that prey on them, Costello and Daane may be able to suggest other ways to keep the pest in check.