A few years ago, citrus trees in Florida just started dying. A disease called citrus greening spread all over the state, wiping out thousands of acres and devastating farmers. The major culprit was a tiny bug called the Asian citrus psyllid that carried the disease from tree to tree. Well, that same bug recently started showing up here in California where citrus is a $2 billion industry.

Farmers are worried that what happened in Florida might happen again. So they're working with scientists to kill off the bug before it's too late and the solution isn't necessarily pesticides. The answer to this problem may be another bug. Steven Jackson has that story.

STEVEN JACKSON, BYLINE: I'm getting the grand tour of Associates Insectary in Santa Paula, California. It's basically a bug farm.

BRETT CHANDLER: I'll take you to where the wasps are being collected now. And the wasps are raised...

JACKSON: That's Brett Chandler. He's the owner. They raise beetles, snails, mites and wasps, bugs that do so many good things for farmers they're called beneficials. In the wasp room, Chandler hands me a little cup, the kind you might get cream cheese in at a deli. This one is full of baby wasps, no bigger than grains of salt.

CHANDLER: I'm guessing in this cup what I see here is about 40,000. And we'll collect 50, maybe 100 cups on a good day.

JACKSON: Associates is one of the oldest insectaries in the world. It's been around since the early 1900s when California farmers first realized they could use bugs to fight pests. Today, we have more and better pesticides than we did back then but plenty of farmers still use bugs too. Farmers like Jose Alcarez. He manages 250 acres of citrus and avocados just down the road.

JOSE ALCAREZ FARMER: I don't want to spray too much because also you kill the beneficials, and also you kill bees, also kill the insect which is used for pollinators. So that's why we try to stay away from the spray.

JACKSON: But when it comes to this new pest, the Asian citrus psyllid, Alcarez will have to spray because there's no bug on the market to fight it. That's where Mark Hoddle comes in. He's an entomologist at the University of California, Riverside. He travels the world looking for bugs. He went to Pakistan where the psyllid comes from and he found something big. Well, actually pretty small. It's a parasitic wasp and it loves to eat the psyllid.

So he brought a few back and started running tests to make sure they wouldn't kill other bugs, good bugs, if they came to California.

MARK HODDLE: And the results were very clear. The parasites we found in Pakistan pose no risk to non-target species. They are very focused on finding Asian citrus psyllid for food.

JACKSON: You kind of have to wonder, wouldn't a simple spray be much easier than this? Why go to all the trouble? The answer is surprising. California has more citrus trees in people's yards than on farms. For those trees pesticides aren't an option because they're not safe to use around lots of people. Besides, it would cost a fortune to spray every tree. And if any of those residential trees were to get citrus greening disease, all it would take would be one psyllid to carry it onto farmland, which would be very bad news.

HODDLE: We don't want the psyllid getting into these commercial areas because it runs the risk of introducing the disease, which will then put us on a similar trajectory to what we have seen in Florida.

JACKSON: That's why Mark Hoddle's wasp is so important. And he's not the only one who feels that way. The California Department of Food and Agriculture has an insectary working full time hatching wasps and releasing them strategically around the state. They're hoping to release 1 million by the end of the year, a big step forward in protecting California farms. For NPR News, I'm Steven Jackson.

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