---
title: "Millions of Sterile Fruit Flies to Be Released in San Diego County"
description: "State and federal agriculture officials are flooding more than 100 square miles of suburban San Diego County with sterile male Mexican fruit flies — a decades-old biological strategy meant to collapse an infestation that has been spreading since a single fly turned up in a La Mesa loquat tree this winter."
category: "California"
category_url: https://herald.la/category/california
author: "Elias Rosen"
published: 2026-06-30T01:48:00.000Z
updated: 2026-06-30T01:48:00.000Z
canonical: https://herald.la/article/millions-of-sterile-fruit-flies-to-be-released-in-san-diego-county
tags: ["agriculture", "pest control", "San Diego County", "Mexican fruit fly", "CDFA", "sterile insect technique", "science"]
---
# Millions of Sterile Fruit Flies to Be Released in San Diego County

State and federal agriculture officials are flooding more than 100 square miles of suburban San Diego County with sterile male Mexican fruit flies — a decades-old biological strategy meant to collapse an infestation that has been spreading since a single fly turned up in a La Mesa loquat tree this winter.

To beat a fruit fly, California is releasing far more fruit flies — just ones that can't have babies.

## One fly, one emergency

On February 24, a routine trap check in La Mesa turned up a single wild, mated female Mexican fruit fly — *Anastrepha ludens* — in a loquat tree, [the California Department of Food and Agriculture said](https://pressreleases.cdfa.ca.gov/Home/PressRelease/67998896). A mated female is the worst-case find: she carries eggs and the potential to seed a breeding population. Within days, the CDFA and the USDA declared a quarantine, which has since grown to about [111 square miles](https://www.countynewscenter.com/mexican-fruit-fly-quarantine-expanded-in-san-diego-county/) covering parts of El Cajon, La Mesa, Lemon Grove, San Diego and Santee as more flies turned up in orange, avocado and other trees.

## Sterile males, futile matings

The centerpiece of the response is the "sterile insect technique," a method California has used against invasive fruit flies since the 1980s. Male flies are raised by the million, then sterilized with a precise dose of gamma radiation at the pupal stage — enough to scramble their reproductive DNA without dulling their drive to mate. Released into the wild, they compete with fertile males; when a wild female mates with a sterile one, she lays eggs that never hatch. Flood the area with enough sterile males and the odds of a successful wild mating collapse generation after generation, wiping out the population over roughly two life cycles, or four to six months. In the San Diego zone, officials are releasing about [250,000 sterile males per square mile each week](https://plantingseedsblog.cdfa.ca.gov/wordpress/?p=22374), dropped from aircraft on repeated passes. The flies are harmless to people, pets and plants — they don't bite or sting.

## Why it matters

The Mexican fruit fly is no picky eater: it can infest more than 50 kinds of fruits and vegetables, including citrus, avocados, stone fruit and tomatoes, with larvae feeding inside and ruining the crop. For California — the nation's largest agricultural producer — a permanent foothold would threaten exports to states and countries with strict pest rules. The pest most often arrives in fruit carried by travelers from infested regions, which is why officials urge people not to bring homegrown or foreign produce across borders. Beyond the sterile flies, the program uses targeted organic Spinosad treatments near detection sites and removes fruit from trees closest to where flies are found.

## What residents must do

Inside the quarantine, the rule is simple: don't move homegrown fruit. Residents are asked to eat backyard citrus, avocados and tomatoes on-site and not carry them off the property; commercial growers face additional requirements. Anyone who spots unusual fly activity, or wants to check whether their address is in the zone, can call the state's pest hotline at 1-800-491-1899. Every prior Mexican fruit fly incursion in California — the first was detected in San Diego County in 1954 — has been eradicated, and officials say they intend to keep that streak intact.

## Sources

- [Mexican fruit fly quarantine expanded in San Diego County](https://www.countynewscenter.com/mexican-fruit-fly-quarantine-expanded-in-san-diego-county/)
- [Mexican fruit fly quarantine in a portion of San Diego County](https://pressreleases.cdfa.ca.gov/Home/PressRelease/67998896)
- [Sterile insects, a key piece of CDFA integrated pest management](https://plantingseedsblog.cdfa.ca.gov/wordpress/?p=22374)