Where Do These Pests Come From?
As their name implies, originally these pests came from Japan. They were first found here in the United States on a plant nursery farm near Riverton, New Jersey in mid August of 1916. Despite initial herculean efforts to wipe them out, they have gradually expanded their territory by flying (usually just a mile or two, but sometimes up to five miles) in search of food. Over the last 81 years the Japanese Beetle has moved north into Maine,west to Wisconsin, and to all parts south and east of a line from there to Alabama plus Missouri. They reached North Carolina in 1932 and Tennessee in 1990. There are even a few localities in California and Oregon have become infected although most western and mountain states remain free of this pest.
Adolescent Japanese Beetles over-winter in the soil as white to cream colored grub worms with brownish heads (about 3/4 to 1 inch long) which you have probably seen as you prepare your garden for planting in the spring. These are the offspring of the successful maters of the previous summer. From their wintering area 8 to 10 inches deep in the ground, each spring the previous year's hatch of grub worms migrate up near the soil surface. There they feed on grass roots until they are ready to transform (pupate) into beetles and come swarming up from their underground development stage.
Likewise, late in the summer you may have noticed brown spots in the grass scattered over your yard. These were evidence that a new crop of Japanese Beetle grubs had hatched out and begun their feast on the roots of the grass in your yard. Dry conditions early in their life can cause eggs and larvae to die; however, wet and moist conditions cause them to hatch out in about 8 to 30 days (faster in warmer temperatures) and grow rapidly. First they eat decayed plant matter. But as they grow they begin to feed on the roots of live plants and tunnel horizontally chewing off roots as they go.
As fall comes the Japanese Beetle grubs dig down deeper into the ground (4 to 10 inches). They can survive ground temperatures of 25 degrees without problems. If the ground gets colder they just move deeper. Then as the ground begins to warm in the spring they move back nearer the surface and resume their feeding on roots. When the soil temperature reaches 60 degrees the will become quite active. Finally around the first of June they will transform themselves into a beetle near the surface of the ground.
Once these adult June Bugs (as the are often called because of the time of year during which they usually appear) complete their transition into a full fledged flying beetle they gather together in massive numbers to forage on your plants ... and mate to start the next generation for the following year.
After feasting on your precious leaves and mating the female lays her batch of 1 to 5 eggs in holes in the ground 2 to 6 inches deep. This cycle repeats every 3 or 4 days until she has laid a total of 40 to 60 eggs. The majority of the females eggs are laid in the first few days of her adult life. Her strong virginal sex attractant scent may have several males waiting for her when she first emerges from the ground after her pupation.
Latest Update on May 24, 1998 by HTML coding by Roger Baxter.
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