(UPDATED COVERAGE 5:25 p.m.) An 88-square mile quarantine of fruits and vegetables has begun in the Rancho Cucamonga area of San Bernardino County after four Mediterranean fruit flies were found in traps.

More than half of the quarantined region is urban, according to the California Department of Food and Agriculture.

“There isn’t any commercial agriculture in that area to speak of,” Steve Lyle, CDFA spokesman, said Aug. 28. “As of last week there was one small growing operation. It was not commercial but a hobby farm. Most of our stuff is done in residential areas.”

Sterile male medflies were released soon after the Aug. 16 finding. They’re being released weekly over an 11-square mile area, 250,000 flies per square mile.

The CDFA is working with the U.S. Department of Agriculture and San Bernardino and Los Angeles county agricultural commissioners on the effort.

“Our system to detect and respond to invasive species like the Mediterranean fruit fly is working well and according to design,” CDFA secretary Karen Ross said in a news release. “The release of sterile medflies is a proven method of eradicating an infestation. The key is to move swiftly and take action before the pests can cause widespread damage.”

Agricultural officials also applied limited treatments of the organic product GF-120 Naturalyte to host trees and plants in a 200-meter radius — about an eighth of a mile — from the sites where flies were found. Residents in treatment areas were notified in advance.

The medfly can infest more than 250 fruits and vegetables. Residents who suspect an infestation can call California’s pest hotline at 1-800-491-1899.