The Japanese Beetles Are Back

The 4-6-week period of intense activity by the gleaming, copper-colored adult Popillia japonica is underway.

These beetles may seem to have it in specifically for your roses, raspberries, crab apples or grapes, but those are just a few of the 300-plus plant species they are known to feed on in North America.

The expert advice might sound counterintuitive: Stop trapping them. (Farewell, beetle bags, despite the marketing promises.) And maybe hold back on watering lawns in the July heat, as female beetles will be seeking a moist spot to lay eggs.

Yes, those are steps toward making peace with this here-to-stay invasive pest, which scientists have sought to subdue since shortly after it was identified in New Jersey in 1916.

Nearly a century later, a 2015 U.S. Department of Agriculture homeowners’ guide to Japanese beetle management put the cost of control in the United States — including the removal and replacement of damaged turf — at $460 million annually. Half of that damage is caused not by the adults, but during the beetles’ larval stage, by the grubs.

Still, this is a troublemaker at both stages of life — and its wide-ranging diet doesn’t hurt its chances, either.

Based on decades of tracking the beetles’ seemingly inexorable march westward in North America, Daniel A. Potter, a professor in the department of entomology at University of Kentucky, described the arc: “The first few decades in a new area, the insect goes crazy and builds to high levels before the population starts to stabilize. Then it goes from a plague to a nuisance.”

For those of us at the nuisance phase, here are some suggestions. But first, some background on the strategies behind the Japanese beetle’s sustained invasion.