They're the bugs with the shiny green backs and the voracious appetites for garden flowers, and they are probably coming to a plant near you.
Japanese beetles seem to be in abundance in the tri-state area this year.
"Yes, very definitely," said Bev Weber, of the Dubuque Arboretum & Botanical Gardens. "I lost a rose bush at home due to them."
First imported to a New Jersey nursery with ornamental plants from Japan in 1916, Japanese beetles have since plagued increasing numbers of American gardeners.
"In the eastern half of the United States, the Japanese beetle is considered the most destructive landscape pest people deal with," said Kenneth H. Holscher, of Iowa State University's entomology department.
Holscher cited two ways in which they are destructive. In their larval stage, they are a white grub that lives in soil and feeds on the roots of turf grass. That causes problems for golf courses. When the adults are out, they will feed on the foliage, the flowers and the fruits of more than 400 plant species.
"These things have a wide variety
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The beetle measures 1/3 to 3/5 inches long. The head and thorax are greenish bronze and the wing covers are copper/metallic-colored. There are prominent white spots at the tip and along the sides of the abdomen. Their feeding causes scarring on the surface of fruits and chewing damage on the margins of leaves and destruction of flowers. They prefer roses, raspberry, grape and crab apple. Damage to field crops is usually limited.
In its native Japan, the beetle's natural enemies keep the population in check and it is not considered a serious pest. In America, a lack of natural enemies has helped the beetle slowly establish itself.
"It has taken 90 years to spread from New Jersey throughout the eastern half of the country," Holscher said.
Japanese beetles only have made limited forays west of the Mississippi River -- including into the eastern portion of Iowa.
"Only about 20 to 25 percent of the counties have had Japanese beetles recorded in them," Holscher said.
Weber said the beetle's local numbers seem to have increased dramatically this year.
"This has been a very prolific year," she said. "We have had so many calls about Japanese beetles, and last year we did not."
An increased beetle population could result from a better-established presence in Iowa, Holscher said, but don't blame the state's unusually wet weather.
"I can't imagine our early spring weather had much to do with it," he said.
Only longer-term weather patterns, Holscher said, could influence the population of insects that produce one generation per year.
"The adults emerge within a six-week period of time," he said, "and they typically will emerge through the month of July."
Each adult lives 30-45 days, Holscher said, so their impact can be felt through the month of August.
"That's a long period of time to deal with them," Holscher said.
Sprayed insecticides can limit damage to plants. Traps also are available.
"But traps are intended to attract Japanese beetles," Holscher said, "so don't put a Japanese beetle trap next to roses."
Holscher expects populations to eventually spread throughout the state.
"I don't think there is any way you can stop the spread of the Japanese beetle," he said.
