For years, some North Carolina blueberry growers knew something was destroying their bushes from below ground. By the time plants showed obvious signs of trouble, it was often too late.
Now, researchers at North Carolina State University say they've identified the culprit: a native longhorn beetle whose larvae can spend years feeding on blueberry roots before the damage becomes visible.
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The discovery marks the first time the species, Prionus imbricornis, has been confirmed attacking blueberries in North Carolina. Researchers say identifying the beetle is a critical first step toward developing tools to help growers protect one of the state's most valuable fruit crops.
"We need to know exactly which species we're dealing with because that's going to help us determine what tools to use," said Lorena Lopez, an assistant extension professor in NC State's Department of Entomology and Plant Pathology. "We also want to answer why blueberries are being infested only here in North Carolina so far."
North Carolina produces roughly $10 million worth of blueberries each year, according to NC State researchers. So far, researchers have confirmed infestations on three farms covering about 1,200 acres.
Hidden underground for years
Unlike many crop pests, the beetles do their damage out of sight.
The larvae live underground, tunneling through blueberry roots for three to five years before bushes begin showing obvious signs of decline.
"The plant doesn't show many distinctive symptoms until the larvae have completely decimated their roots," Lopez said. "Most of the canopy continues to produce fruit, so growers may mistake the damage for disease or nutrient deficiencies."
By the time bushes begin dying, nearby plants may already be infested, making the pest especially difficult to manage.
Solving the mystery with DNA
Growers first brought the unusual larvae to Lopez after noticing bushes dying in eastern North Carolina blueberry fields. While researchers could identify the insects as members of the Prionus genus, several closely related species live across the Southeast, and their larvae look nearly identical.
To determine which species was responsible, researchers collected adult beetles and larvae, sequenced their DNA and matched the genetic fingerprints.
"If we don't know the specific species, then we don't know how to tailor the management properly," said Kenneth Geisert, the study's lead author and a doctoral student at NC State. "The larval sequences matched Prionus imbricornis, allowing us to scientifically say this is the exact species causing the problem."
Looking for solutions
The discovery does not immediately solve the problem for growers.
There are currently no insecticides labeled specifically for controlling the beetle in blueberries. Lopez's lab is now testing insecticides to determine whether treatments can target newly hatched larvae before they burrow deep into plant roots.
Researchers are also studying whether pheromone traps could help reduce beetle populations without relying solely on pesticides.
For now, Lopez encourages growers to keep fields as healthy as possible and watch for declining plants, especially in older fields.
Could drought be playing a role?
Researchers are also investigating whether environmental conditions could be making blueberry plants more vulnerable.
Geisert said insects can respond to drought and other environmental stress by changing when they emerge or, potentially, by shifting to different host plants. While researchers know Prionus imbricornis typically feeds on hardwood trees, they are exploring whether stressed blueberry plants may be becoming more susceptible.
"We're seeing them potentially shift to blueberries, not because blueberry bushes are an ideal host, but because the climate is putting a lot of stress on these blueberries," Geisert said, emphasizing that researchers are still studying the relationship.
Lopez said many questions remain, including why the beetle has only been confirmed attacking blueberries in North Carolina.
"Thanks to collaborations through NC State and the North Carolina Blueberry Council, we've been able to make progress," she said. "Hopefully in the years to come, we'll answer some of those biology and ecology questions about this pest."
