Swarms of parasitic wasps will descend upon Kona coffee farms this spring as a long-gestating plan to control an invasive pest finally goes forward.

The coffee berry borer is a destructive invasive beetle that has been devastating to coffee farms worldwide. First discovered on the Big Island in 2010, its name is attributed to its boring into coffee berries to lay eggs, ruining farmers’ yields.

The state Department of Agriculture in 2023 announced a plan to import a species of parasitic wasp, Phymastichus coffea, that would naturally target and infest the beetle in order to reduce its population. Nearly two years later, those wasps finally are here.

“I believe they only just arrived in the state in the last month,” said Jonathan Ho, plant quarantine manager at the state DOA, who added that complications in the federal import permitting process delayed the bugs’ arrival.

Ho did not have an estimate for how many wasps have been imported, but two populations currently are being raised at facilities in Volcano and on Oahu. The insects must be reared in a secure environment for at least two generations — little more than a week, as adult males live for one to two days, and adult females for three to four — to ensure they do not have their own parasites that could spread to local wildlife.

DOA will hold the bugs for much more than two generations, however. Ho said DOA is hoping to release the wasps around April to hit the coffee growing season.

Ho said biocontrol agents like the wasps are typically released in small batches so researchers can evaluate their efficacy.

“We want to make sure a population is able to survive in the wild beyond a single generation before we release more,” Ho said.

Mark Petersen, president of the Kona Coffee Farmers Association, said he expects the DOA will tent individual trees at first and then release the wasps within those tents before conducting any wide releases.

The wasps, when released, should lay eggs in the bodies of the borers. When the eggs hatch, the larvae consume the borer, quickly mature and seek more borers to parasitize.

The process has been found to be effective in other countries suffering from the beetle. At the same time, there has been no recorded instance of a Phymastichus coffea specimen parasitizing a different species, so the risk of the wasps targeting native species is low.

The wasp also is particularly tiny — about the size of a gnat — and does not sting humans or animals.

If successful, the wasp will be a welcome friend to West Hawaii coffee farmers, who have found managing the borer to be a constant battle.

“I’m all in favor of having more tools in our tool belt,” Petersen said.

“(The borer population is) not thinning, and it’s definitely not controlled,” said Tom Greenwell, co-owner of the roughly 200-acre Greenwell Farms in Kealakekua. “We do a fairly good job, and we can keep below 10% (crop loss). But we have to work hard to get below 10%.”

Petersen said his own coffee operation has seen a higher infestation rate in 2024 than the previous year, jumping from an estimated 12% rate to more than 40%.

Petersen said the most popular control method against the borer can still be unreliable. A popular fungal pesticide — which infects the borer with a hostile fungus — is effective at killing the bugs, but only as a contact spray, meaning it has to be used just at the right time to be effective.

That pesticide, Petersen said, can be expensive, running about $250 for a one-gallon bottle. While he didn’t estimate how many acres a bottle of that size can last, Petersen said it’s common for farmers to burn through many bottles each season.

Other control methods require constant maintenance of coffee trees to prevent the borers from gaining a foothold, which can be all for naught if a neighboring field is not also being similarly maintained.

“Any time you have any crop left over after the harvest, you’re going to have a hard time next year,” Greenwell said, adding he has seen some farmers lose 60% of their total crop.

The borer also reduces the quality of the coffee, Greenwell said, with the presence of borers and their larvae breaking down the coffee bean and leaving a foul taste.

“It’s not a good taste,” Greenwell said. “And we’re a gourmet coffee company. We can’t sell it if it’s not good.”

Greenwell said he’s hopeful about the wasp strategy, whose progress he has followed since it was announced. He said he has heard from farmers in other countries, such as France, who have stopped using the fungal pesticide because the wasp so effectively cut the borer’s population.

“It’s exciting news,” Greenwell said. “They can definitely release it on my farm if they want.”