Five-Inch Beetle Grubs Eating NC Blueberry Roots Identified by DNA
NC State scientists used DNA barcoding to name the longhorn beetle whose five-inch larvae eat blueberry roots. No insecticide is labeled for it yet.
A longhorn beetle whose larvae can grow five inches long is the insect chewing through blueberry roots in North Carolina, researchers at North Carolina State University reported. DNA from larvae found on farms matched the species Prionus imbricornus at 98 to 99 percent, which settles a question growers have lived with since reports of root damage began in 2010.
The answer comes with a problem: no insecticides are currently labeled for use against this pest in blueberries, according to the study’s authors. North Carolina is the first state to document the species feeding on blueberry bushes.
A root feeder that hides underground
P. imbricornus is a wood-boring beetle with long antennae. Females usually lay their eggs in soil close to the roots of hardwood trees. The larvae hatch and feed on those roots, sometimes eating enough tissue to kill the tree, while the adults do not feed at all. On blueberry farms, the same underground feeding damages the bushes and can kill them.
Growers had seen unidentified Prionus larvae damaging blueberry roots for more than a decade, but no one could say which species was to blame. The grubs stay below ground near the roots, so they are hard to find. Larvae of different longhorn beetle species also look very much alike, which makes identification by eye unreliable.
How the team matched larvae to adults
The field work took place at six blueberry farms in Pender, Sampson, Bladen and New Hanover counties. Researchers set up black panel traps baited with sex pheromones, the chemical signals beetles use to find mates, to catch adult beetles.
They then ran genetic barcoding on larvae collected in the fields. The technique reads short, standardized stretches of DNA and compares them with reference sequences from known species. Matching larval DNA against DNA from adult Prionus beetles produced the 98 to 99 percent match with P. imbricornus.
The results appear in the Journal of Integrated Pest Management (DOI: 10.1093/jipm/pmag018). Kenneth Geisert, a graduate student in NC State’s College of Agriculture and Life Sciences, is the lead author. His co-authors are Lorena Lopez, an assistant extension professor in the Department of Entomology and Plant Pathology, and Gareth Powell, an assistant professor who directs the NCSU Insect Museum. The paper’s title spells the species name imbricornis, while the university’s announcement uses imbricornus.
Why it matters for blueberry growers
Pest control depends on knowing which insect is present and how it lives. Geisert said researchers had often assumed which Prionus species they were facing based only on the adults. A wrong guess, he said, can lead to a treatment that does not fit the problem. One longhorn species may attack roots while another goes after a trunk or dead branches, and the wrong approach can harm insects that were never the target.
Lopez called the finding both good and troubling news. Pinning down the species is very important, she said, yet North Carolina was the first state to report the infestation in blueberries, and growers still have no labeled insecticide against it.
What comes next
Lopez has started testing insecticides to see which ones might control the beetles. Timing is a main focus. The team wants to schedule treatments around the beetles’ reproductive cycle so that larval development is disrupted before the grubs do heavy damage to roots. The published study identified the pest; whether any treatment works is still being tested.
Source: ScienceDaily
