The steamy summer has triggered the region's worst Japanese beetle infestation in nearly two decades, sending gardeners and nursery owners scrambling to stop the ravenous insects from devouring flowers, trees, shrubs and lawns.

The beetles are munching their way through the area, reproducing relentlessly and turning roses, hibiscus bushes and linden tree leaves -- among the almost 300 species of plants that host the beetle -- into skeletons.

"I think it's pretty spectacular," said entomologist Mike Raupp, who has studied insects at the University of Maryland for decades. "It's sort of an extravaganza of Japanese beetles."

Last summer's rains coupled with this season's scorching temperatures and tropical humidity have fostered what entomologists call the perfect climate for Japanese beetles to thrive. What's more, the region's lush green foliage has accelerated the beetle's reproduction activity.

"It's warm 24/7, so the beetles are up in the trees partying. They're feeding; they're mating," Raupp said. "It's a big beetle party right now."

Japanese beetle infestation is an annual rite in the eastern United States, although it is a particularly mighty one this year. Reports of the beetles' arrival first surfaced about three weeks ago, officials said.

Beetle traps are selling like hotcakes at nurseries across the region. Behnke Nursery in Beltsville already has sold out of its stock of the traps, sales manager Sean Henderson said.

Horticulture is a $1 billion industry in Maryland and is the state's second-largest agricultural industry, behind poultry. It's too early to determine the full extent of the harm caused by the infestation, but nurseries said their plants are suffering.

"It does slow the growth of the trees down," said Kelly Lewis, a manager at Ruppert Nurseries in Laytonsville, where beetles are damaging red-leafed flowering plum trees and linden trees. A tree that normally takes three to four years to grow enough to put on the market might take five years if it has been damaged by Japanese beetles, Lewis said.

"We're seeing significant damage to plants," agreed Paula M. Shrewsbury, an entomologist at the University of Maryland.

The pests typically emerge in mid-June, reach a peak in mid-July and remain active for about four to six weeks, according to the Maryland Cooperative Extension. They measure just under a 1/2 inch long and are metallic green with bronze-colored, hardened wings.

The Japanese beetle, or popillia japonica, is an exotic species that arrived in the United States from Japan in 1916, first appearing in a southern New Jersey nursery. It mostly lives east of the Mississippi River where the soil is moist, but the beetles have ventured to the more arid western states by hitching rides on cargo trucks and airplanes, Purdue University entomologist Timothy J. Gibb said.

They feed on ornamental plants and are particularly fond of roses and flowers of all kinds, as well as trees that grow fruit. They nibble away at the soft, meaty parts of the leaves, leaving behind only the harder veins.

"They kind of lace the leaves," Lewis said.

Typically, in July, the beetles lay eggs, which hatch within about 10 days. The C-shaped grubs are creamy colored with brown heads, have three pairs of legs and are about an inch long when fully grown. They feed on the roots of such turf grasses as Kentucky bluegrass, ryegrass and bent grass. Root loss from grubs can be so extensive that the turf can be rolled back from the soil like a rug.

The beetles fly, making them very mobile, and they flock in large numbers to attractive climates, said Clifford S. Sadof, an entomologist who studied Japanese beetles at the University of Maryland before transferring to Purdue.

"They're around in cities because there's lots of ornamental plants for adults to feed on and there's enough turf roots for the grubs to feed on," Sadof said.

Michael Schauff, associate director of the U.S. Department of Agriculture's plant sciences institute, said he has personally noticed an increase in Japanese beetles in the Washington area in recent weeks.

"I generally first notice them doing damage to my ornamental plants -- hibiscus and crape myrtle in particular," Schauff said.

Montgomery County Cooperative Extension master gardener Carole Dyer said gardeners can use a variety of methods to kill the beetles. They can pick them off of plants and trees by hand; grow different plants that are not favored by the beetles; use dishwashing soap or insecticides, such as or pyrethrum blends; or spread commercial beetle traps.

Staff researcher Bobbye Pratt contributed to this report.

Japanese beetles feast on hundreds of plants. Grubs eat lawn roots, and adults pick leaves clean. Gardeners can fight back with traps and insecticide.