Center Funding Helps Develop a Better Way to Control Prionus Beetles

Adult Prionus beetles
Adult Prionus beetles.

Hops growers in the Northwest – as well as sweet cherry, apple and other fruit growers around the nation – now have a new tool to combat Prionus beetles and their root-boring larvae thanks to research funded in part by the Western Integrated Pest Management Center.

The research identified a sex pheromone produced by female Prionus californicus beetles and developed a synthesized version being developed by Pacific Biological Control as a commercial mating-disruption product.

“Every year, the Western IPM Center supports new pest-management research in the West, and this is exactly the kind of impact we’re looking to make,” said Jim Farrar, the director of the Center. “There really was no good way to manage this pest, and now we’re seeing an effective solution.”

The adult Prionus californicus beetle is a fierce-looking longhorn beetle about two-inches long. The adult beetle doesn’t eat or drink and has a short three-to-four-week lifespan devoted to finding other beetles to mate with. The damage is done by the larvae.

“The larvae are root-feeders,” said Jim Barbour at the University of Idaho who co-led the Center-funded research team with Jocelyn Millar of the University of California, and Lawrence Hanks of the University of Illinois. “They grow to about three inches long, and one or two of them really make a mess of hop roots and the roots of some fruit trees. In fact, one old name for the beetle was the Giant Apple Root-Borer.”

Once a hop yard is infected, the only effective control strategy has been pulling up the plants and leaving the field fallow for two or three years. Fumigation with various organophosphates is sometimes used, but its effectiveness is questionable.

“In Idaho, they are the most serious hop pest,” Barbour said. “They are also a problem in Washington as well, which is the largest hop-producing state with about 25,000 acres in production.”

The team determined the female Prionus beetle produces a sex pheromone, then identified and synthesized the compound.

“Since then, it’s been shown to attract a number of Prionus beetles, not just Prionus californicus,” Barbour said. “It works with at least eight different species in North America and one in Europe.”

The team tested its compound in both mass-trapping strategies and mating-disruption approaches. In the former, the bait scent is placed in traps that beetles fall into and can’t escape and they die in the traps. In the latter, enough of the scent is released to saturate an area so the beetles can’t follow it back to a female and they die naturally without having mated.

“Mating disruption is easier in some respects because you don’t have traps to manage,” Barbour said. “It takes more work up front to show that the beetles are not finding each other to mate.”

The team’s tests showed both approaches can work, but have focused on mating disruption.

Barbour’s current research team is working with Pacific Biological Control and Western Region IR-4 to get the compound labeled by the EPA as a mating disruption agent for use in hops and sweet cherries. Since both are small-acreage crops, expanding the approved use to other crops like apples and pecans could help make the product more economically viable.