It is a sight frustrated coffee farmers might line up to see — a hungry predator beetle devouring the larvae of the pestilential coffee berry borer.
Researchers at the U.S. Pacific Basin Agricultural Research Center took that video inside a coffee bean just a few days ago using a microscope, part of a research project that could eventually lead to the square-necked grain beetle being used as biocontrol.
Researchers have known for years that the beetle dines on the tropical nut borer that has been the bane of macadamia orchards. While it’s too early to know if the insect could also help munch down populations of the coffee pest, scientists are encouraged by this latest finding.
“We’ve shown that in the lab they will gobble CBB eggs and larvae,” said research center entomologist Peter Follett. “But we were never really sure it was feeding on CBB inside the bean.”
Researchers sampling coffee cherry from 180 farms have found the beetle is widely distributed, and have assumed it eats borers and other insects. The predator is the right size to fit into the holes created by the borers. In earlier tests, researchers put cages over the branches of infested cherry and released the beetles inside. Within a week, the predators were inside the beans, in cavities created by the borer.
In coming days, the research center will gather fresh supplies of the grain beetle from West Hawaii coffee cherry for additional testing. Entomologists want to study how much of the beetle’s diet is composed of the coffee pest.
“We’re trying to learn everything we can about it,” Follett said. “Whether it will actually have an impact on CBB will require a lot more study. It’s a stored grain pest, so it’s easy to rear in large numbers in cracked corn.”
Supported by grants from the federal and state departments of agriculture, scientists are also studying a close relative of the square-necked grain beetle which, so far, appears to behave in similar ways.
Biocontrol is seldom effective on its own, but the beetles — raised and released to increase wild populations — could be one tool in the fight to keep borer numbers down, Follett said.
Kealakekua coffee farmer Bob Nelson is helping gather samples for the study. He’s also aiding researchers in mapping the distribution of the square-necked grain beetle. Nelson harvests borer-infested cherry every two weeks from low, medium and high-elevation farms throughout the coffee belt, so it can be examined for evidence of the beetle.
So far, the predator has been found in 20 to 40 percent of coffee berry borer-infested “raisins,” or dried cherry.
“We certainly need something to keep the numbers down on CBB,” said Nelson, owner of Lehuula Farms. “There’s no silver bullet that’s going to eliminate it. We’d like a number of tools to combat it.”
“People are going to ask, ‘what else is it going to do?’” he said. “But it’s already here. That means it’s going to do what it’s going to do anyway.”