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Photo of beetle on geraniumBinged-Out Beetles

by Jonathan Riggs

Another round of geranium petals seems to be the order of the day for thrill-seeking Japanese beetles. It seems that after feeding on these petals, Japanese beetles get so intoxicated that they pass out for 12 to 18 hours. In the wild, this can be a lethal binge.

Drawing on research done in the 1920s, UK entomologists Daniel Potter and David Held have been studying this phenomenon, trying to figure out what exactly in the geranium causes such a powerful reaction.

Since the Japanese beetle feeds on 300 plants and 79 plant families, including many plants grown for profit or pleasure, researchers are always looking for new, earth-friendly methods of controlling them. The geranium's knockout punch offers an intriguing possibility.

"We found that when Japanese beetles fed upon the petals of geranium, generally in less than an hour the bugs enter a kind of narcotic state," says Potter. "They curl up on their back and pull their legs close to their underside. They'll twitch if you disturb them, but they're clearly in dreamland."

Funded by the U.S. Department of Agriculture, Potter and Held have found that plants grown in full sunlight pack more of a culinary wallop for Japanese beetles.

And the bugs seem unable to resist temptation. When researchers gave beetles who had never encountered a geranium a choice between the nutritious linden plant and the mind-blowing geranium, the beetles overwhelmingly chose geranium and ended up staring up at the sky. Each time the beetles recovered, they chomped down another helping of petals and all but ignored the healthy choice.

Potter's team reared pairs of beetles in boxes with soil so that they could lay their eggs. One group received the healthy linden leaves, one group received the geranium petals, and one group received an equal amount of both.

"As one would expect, the group that got the linden leaves lived long and happy lives and laid a large number of eggs," says Potter. "Both groups with access to geranium spent the better part of this two-week experiment on their backs in a narcotic state, had a much higher mortality rate, and laid very few eggs."

Unlike certain caterpillars, Japanese beetles seemed unable to learn. In fact, each time they recovered from a geranium-trip, they would consume almost 10 times the previous amount before becoming intoxicated.

In theory, an insect that views nature as its personal buffet, like the Japanese beetle, should be able to learn from this type of bad experience.

"Of course, we're presuming this is an unpleasant experience for the Japanese beetle," says Potter. "Clearly their nervous system is being affected and perhaps that's compromising their ability to learn. It certainly has some parallels to human addiction, although I don't think it's quite the same phenomenon."

With the help of plant chemists at Boyce Thompson Institute at Cornell University, UK researchers are testing various geranium chemicals on the beetle-favorite Virginia creeper, and they've been able to duplicate the geranium's narcotic effects. Potter says that by this coming summer they'll have identified the exact extract.

This knowledge should prove useful in further Japanese beetle control research.

"One of my goals is to understand the insect better," says Potter. "I think if you understand the biology of a pest insect, it opens up new avenues for management that are environmentally more responsible."

Japanese beetle management is serious stuff—almost all of the states east of the Mississippi River except Florida suffer tremendous financial damage from the ravenous insects. This research is part of the USDA's effort to prevent the Japanese beetle from spreading to the western United States, where it could devastate such economic mainstays as the California vineyards.

The Japanese beetle's behavior makes it an interesting insect to study, Potter says.

"I really like the Japanese beetle. It's my bread and butter insect. It's a great bug, sort of The Terminator of the insect world."