On September 14, 2023, and again on October 3, 2023, the Animal and Plant Health Inspection Service (APHIS) and the California Department of Food and Agriculture (CDFA) expanded the Zeugodacus tau fruit fly quarantine in the Stevenson Ranch area of Los Angeles County, California. These actions are in response to the confirmed detections of 36 adult flies from various trapping sites in the Stevenson Ranch area by CDFA between September 1 and September 29; all were from traps in residential areas. As a results of these detections, the Stevenson Ranch area quarantine increased by ten square miles to 110 square miles. There is no commercial agriculture in the quarantine area.

APHIS and CDFA established the original Z. tau quarantine on July 11 following the confirmed detection of nine flies in the Stevenson Ranch area between June 7 and July 6, and expanded the quarantine on August 15 following detections of additional flies. APHIS is applying safeguarding measures and restrictions on the interstate movement or entry into foreign trade of regulated articles from the area to prevent the spread of Z. tau to non-infested areas of the United States. APHIS is working with CDFA and the Los Angeles County Agricultural Commissioner to respond to these detections following program guidelines for survey, treatment, and regulatory actions.

On October 3, 2023, APHIS and CDFA expanded the Oriental fruit fly (Bactrocera dorsalis or Oriental Fruit Fly, OFF) quarantine in San Bernadino and Riverside Counties, California. This action is in response to the confirmed detections of 72 adult flies from various trapping sites in the Redlands area by CDFA between September 28 and October 3; all were from traps in residential areas. As a results of these detections, the Redlands area quarantine increased by ten square miles to 112 square miles. There are approximately 1,200 acres of commercial agricultural production in the quarantine area.

APHIS and CDFA established the original OFF quarantine on September 27 following the confirmed detection of eight flies in the Redlands area between September 18 and September 23. APHIS is applying safeguarding measures and restrictions on the interstate movement or entry into foreign trade of regulated articles from the area to prevent the spread of OFF to non-infested areas of the United States. APHIS is working with CDFA and the Agricultural Commissioners of San Bernadino and Riverside Counties to respond to these detections following program guidelines for survey, treatment, and regulatory actions.

The expansion of these quarantines is reflected on the APHIS fruit fly website, which contains a description of all current federal fruit fly quarantine areas. APHIS will publish a notice of these changes in the Federal Register.

Under IPPC standards, Zeugodacus tau is a transient pest under eradication that is present only in one area in California. Bactrocera dorsalis is a transient pest under eradication that is present only in four areas in California. These species are not widely distributed and are under official control in the United States.