North Carolina blueberry growers are confronting a destructive longhorn beetle whose underground larvae feed on plant roots and can kill blueberry bushes. Researchers at North Carolina State University have identified the suspected pest as Prionus imbricornus, resolving a mystery that has affected the state’s blueberry fields for more than a decade and providing a basis for developing targeted controls.
A decade-old mystery beneath blueberry fields
Prionus imbricornus is a longhorn beetle distinguished by its long antennae. The wood-boring insects are becoming a concern for blueberry growers across North Carolina.
Female beetles typically lay their eggs in soil near the base of hardwood trees. After hatching, the larvae feed on roots and can sometimes destroy enough tissue to kill the plant. The larvae can grow to 5 inches long, while adult beetles do not feed.
North Carolina was the first state to document P. imbricornus feeding on blueberry bushes, but similar symptoms had been reported for years. Reports of an unidentified Prionus species and outbreaks of larvae damaging blueberry roots date back to 2010. Researchers had struggled to determine which species was responsible.
The insects’ underground habitat made the problem difficult to investigate. Larvae remain close to plant roots, where they are difficult to find and study. Larvae from different longhorn beetle species can also look very similar, making visual identification unreliable.
This uncertainty makes it difficult to develop appropriate pest-control strategies, said Kenneth Geisert, a graduate student in North Carolina State University’s College of Agriculture and Life Sciences and the study’s lead author.
“In the past, researchers often simply assumed species; if that assumption is wrong, it could mean using treatment strategies that don’t match the problem and incorrectly linking species to their hosts,” Geisert said. For example, P. imbricornus longhorn beetles attack roots, while other longhorn beetle species may attack tree trunks and dead branches. Managing the pest without understanding the target beetle’s species and ecology could also harm non-target insects.
DNA analysis identifies the beetle
To identify the insects, the researchers conducted field surveys at six blueberry farms in North Carolina’s Pender, Sampson, Bladen and New Hanover counties.
They installed black panel traps containing sex pheromones, chemical signals that attract adult insects. After collecting the beetles, the scientists used a DNA identification method known as genetic barcoding to identify larvae found in the fields.
Genetic barcoding examines short, standardized sections of DNA and compares them with reference sequences from known species. By matching DNA from unidentified larvae with genetic material from adult Prionus beetles, the researchers could determine which species were present.
The analysis showed 98–99% agreement, confirming P. imbricornus as the beetle associated with the root damage.
A pest without approved insecticides
Identifying the pest is an important advance, but it also highlights a serious challenge for blueberry growers.
Lorena Lopez, an assistant professor of extension in North Carolina State University’s Department of Entomology and Plant Pathology and a co-author of the study, said the discovery brings both good and worrying news.
“On the one hand, it’s very important to know what species we’re dealing with,” Lopez said. “On the other hand, North Carolina was the first state to ever report it. P. imbricornus is widespread in blueberries, and there are currently no insecticides labeled against this pest of blueberries.”
Lopez has begun testing insecticides to determine which treatments could effectively control the beetles.
A central goal is to identify the best time to apply treatment. By coordinating insecticide applications with the beetle’s reproductive cycle, researchers hope to disrupt larval development before the insects can cause extensive damage to blueberry roots.
If successful, the approach could give farmers a much-needed way to protect their crops from a pest that has been difficult to identify and manage for more than a decade.
The survey results were reported in the Integrated Pest Management Journal in a paper titled “Prionus imbricornis (Coleoptera: Cerambycidae), an emerging pest of blueberries in North Carolina.” Gareth Powell, an assistant professor at North Carolina State University and director of the NCSU Insect Museum, also contributed to the study.
Source: www.sciencedaily.com
