According to the Agriculture Research Service (ARS), each year Japanese beetles (Popillia japonica Newman) cost the ornamental plant industry $450 million in damage. A half inch in length, with a body that is shimmering green, wings that are a metallic copper, and a head that is bluish-green, these pests are hard to miss, as is the destruction they wreak in our gardens. They feast on a wide variety of plants, including ornamentals, soybean, maize, fruits and vegetables. As their diet includes 300 plants and 79 plant families, scientists have become increasingly interested in how to eradicate these seriously destructive insects.Although as of 2010 they have remained in the eastern United States, if they were to spread to the western United States, they could conceivably devastate such major economic mainstays as the California vineyards. Therefore, UK entomologists Daniel Potter and David Held, funded by the U.S. Department of Agriculture, are searching for planet-friendly methods of eradication.Previously the USDA has recommended spraying attractant plants, such as the geranium, with insecticide spray formulated with acephate, carbaryl, malathion or rotenone; these are extremely effective against Japanese beetles. But as we become increasingly aware of the delicate balance of our planet and how we can deal with destructive pests in a more earth-friendly manner, the scientists are looking more closely at precisely why the geranium is so attractive to the beetle.
In drawing on research from the 1920s, Potter and Held, along with the assistance of chemists at Boyce Thompson Institute at Cornell University, and, in a separate study, ARS entomologist Chris Ranger in Wooster, Ohio, have found that the geranium when ingested produces a narcotic dream-state that is addictive. Beetles feed on the plant, and in about an hour they pass out for as long as 18 hours, making them easy prey for predators such as hungry starlings.
Ingesting the geranium causes them to be less fertile, with shortened life spans, consequently resulting in a declining insect population. And for a reason that the scientists have yet to ascertain, geraniums growing in full sunlight have more of a narcotic effect than those growing in partial shade.
The substance in geranium that drugs the Japanese beetles is geraniol, which is also found in some other flowers; in the UK, tests are being done to see if the beetle-favorite Virginia creeper duplicates the geranium’s narcotic effects.
Mirroring the actions of human addicts, even after awaking from their drugged stupor, the Japanese beetles will immediately begin eating again. When offered the tasty and nutritious linden plant along with the geranium, the beetles chose the latter, ending up paralyzed, staring up at the sky.
When pairs of beetles were given environments containing soil so that they could lay eggs, scientists gave one group the linden plant to feed upon, another only geranium and a third group a mixture of both. The beetles who had solely geranium or partially geranium diets laid fewer eggs, lived shorter lives, and spent the better part of their time in a narcotic state.
Gardeners can help keep down the Japanese beetle population by planting geraniums throughout the garden. Then, place a bucket of water beneath your geranium plants and shake the paralyzed beetles into it. Kill any beetle grubs on the ground by applying milky spore bacteria powder around the bottom of the plants; this is a natural powder toxic to beetle larvae. Also plant repellant plants such as catnip, chives, garlic, rue, mirabilis, larkspur, and red buckeyes (whose flowers attract and poison the beetles).