North Carolina’s blueberries may have a beetle problem. For the first time, scientists in the Tarheel State have documented the presence of Prionus imbricornus eating blueberry bushes. This longhorn beetle and its larvae can chomp their way through the state’s valuable blueberry fields. The findings are described in a study published this week in the Journal of Integrated Pest Management.
Blueberries are native to North Carolina, but were not cultivated until 1935. The state is the sixth largest blueberry producer in the United States, and the blueberry industry is valued at roughly $70 million. Protecting the plants from pests is crucial, as blueberries are considered one of North Carolina’s most valuable and desirable crops.
Several species including the blueberry maggot (Rhagoletis mendax), plum curculio (Conotrachelus nenuphar), and cranberry fruitworm (Acrobasis vaccinii Riley) can threaten blueberry crops. The long-horned beetle P. imbricornus may now join their ranks. P. imbricornus is known for their long antennae and are considered wood-boring beetles. The adult females typically lay their eggs in the soil near the roots of hardwood trees. The larvae then eat and destroy the roots. These larvae can grow up to five inches long and potentially kill trees, since the adults don’t feed.
North Carolina is the first state to report that P. imbricornus is actively feeding on blueberry bushes. However, reports of unidentified larvae from the Prionus beetle genus feeding on and damaging blueberry bush roots go back to 2010. In the 16 years since, identifying the specific species responsible has been difficult since the larvae live near the roots of the plants. Different types of longhorn beetle larvae also look very similar, and not identifying a species can harm efforts to combat harmful bugs.
“Before now, researchers often just assumed the species of Prionus on their commodities based on adult identification,” Kenneth Geisert, a study co-author and NC State graduate student, said in a statement. “If that guess was incorrect, it could mean using a treatment strategy that did not line up with the problem and incorrectly associating species and their hosts.”
For example, P. imbricornus attacks roots, but another longhorn beetle species may go after a tree’s dead branches or trunk.
“Without knowing which species of beetle you’re dealing with and their ecology, incorrect management can cause adverse effects on non-target insects,” Geisert added.
For this study, the team used a series of black panel traps scented with sex pheromones to attract and gather adult beetles. The traps were placed at six farms across Pender, Sampson, Bladen, and New Hanover counties. The team then used a technique called genetic barcoding on the larvae to analyze small, standardized segments of their DNA to identify the species. They then compared the unknown larval sequences with the same genetic segments from known Prionus adults.
They matched the P. imbricornus with 98 to 99 percent accuracy. According to the team, this result is both good and bad news for farmers.
“On one hand, it’s very important that we know which species we’re dealing with,” said Lorena Lopez, a study co-author and entomologist at NC State. “On the other, North Carolina was the first state to ever report Prionus infestation in blueberries, and there are no insecticides currently labeled against this pest in blueberries.”
To address this shortfall, Lopez has begun insecticide trials. Pinpointing effective insecticides and timing during P. imbricornis reproductive cycles can potentially limit larval development. Fewer larvae could help prevent major root damage and provide blueberry farmers with an effective management tool to protect their crops.
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