Millions of Sterile Fruit Flies Will Soon Be Dropped on Los Angeles

The influx of insects is meant to combat the invasive medfly, after officials identified two of the produce-destroying creatures in the area

A fly on a leaf
A Mediterranean fruit fly (Ceratitis capitata), also known as a medfly USDA ARS Photo Unit via licensed under CC BY 3.0 US DEED

In October, agricultural officials in California discovered two fruit flies in the Leimert Park neighborhood of Los Angeles, prompting a 69-square-mile quarantine. Now, officials plan to release more than two million sterile male fruit flies into the city in an attempt to eradicate the insects. 

While this might seem like an overreaction, these were not just any flies. Called Mediterranean fruit flies (Ceratitis capitata), or medflies for short, they are an invasive species that can infest more than 250 types of fruits and vegetables. This makes them the “most important agricultural pest in the world,” per the United States Department of Agriculture.

Female medflies lay their eggs inside produce, and when the eggs hatch into maggots, they’re destructive. The larvae tunnel through the crops, causing them to rot and become inedible. 

The quarter-inch insects are native to sub-Saharan Africa but have been found in the Mediterranean region, southern Europe, the Middle East, Western Australia, South and Central America and Hawaii. As people move infected fruit to different locations, the flies spread to new areas. 

If medfly populations are left unchecked, officials say they could devastate California’s billion-dollar agricultural industry. 

“Growers would go out of business; packing houses would go bankrupt; the damage would be in the billions,” James Cranney, the president of the California Citrus Quality Council, tells Livia Albeck-Ripka of the New York Times. It would be an “untold level of catastrophe.”

So, to combat the insects, officials will drop 250,000 sterile male flies per square mile across a nine-square-mile area each week. These flies, which are specially grown at a military base in Los Alamitos, are marked with purple dye. They will be flown over the city in an airplane then “released out of the bottom of the cabin,” as Ken Pellman, a press representative for the Los Angeles County Agriculture Department, tells SF Gate’s Ariana Bindman. When these males mate with females, the resulting eggs are infertile and so small that they don’t affect crops.

California has been battling medfly infestations for decades. The first insect was detected in the state in 1975, but it wasn’t until between 1980 and 1982 that the flies reached outbreak levels. Then-governor Jerry Brown authorized an aggressive aerial campaign spreading the insecticide malathion to knock out the flies, which prompted backlash from Californians who were unhappy the chemical was being sprayed across their neighborhoods.

The state declared the flies eradicated in 1982, but another infestation broke out seven years later, in 1989. This time, the spread seemed unusual. Flies were popping up right outside spray zones in an unnatural female-to-male ratio—and there didn’t seem to be enough larvae to account for all the adults being spotted. In December of that year, a group calling themselves “The Breeders” claimed in a letter that they were responsible for spreading medflies in retaliation for the state’s ongoing malathion sprays. It’s still unclear who was responsible for the letter, or if the alleged vengeance was really the cause of the 1989 outbreak. Others proposed that perhaps the flies were never truly eradicated in the early 1980s or that people had brought more infected fruit into the state. 

In 1990, California stopped its malathion spraying, because it didn’t seem to be working, switching instead to the method preferred today: releasing sterile males.

Medflies aren’t the only fruit flies that have been invading California recently. In late October, the state issued a 76-square-mile quarantine after two Queensland fruit flies were found in Ventura County. This was the first quarantine in North America for this particular species, writes KTLA 5’s Marc Sternfield. And in July, the discovery of 20 invasive Tau fruit flies prompted a quarantine in the Santa Clarita Valley. 

“California is facing an agricultural crisis,” Ventura County Agricultural Commissioner Korrine Bell said at a news briefing, per KTLA 5. “There’s been an unprecedented outbreak of fruit flies throughout the state.”

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