Japanese Beetle Life History
The Japanese Beetle spends most of its one year life cycle as a white grub. Ten months to be exact. The other two months are spent as an adult. The adult emerges from the soil in late June and remains above the soil throughout July and August. The peak period for Japanese beetles is July. Between the female feedings, they will dig about 3 inches into the soil and lay up to four eggs at a time. The female will lay 40-60 eggs during these months. The best conditions for these beetles are well watered and well fertilized lawns rich in nutrients. The adults can live up to the first frost. The grubs will burrow their way 4-8 inches into the soil where they will hibernate (just like bears) through the winter. The following year, they rise to the root layer of the lawn and feed on the roots until they emerge as adults in late June.
Pest Control Options
This is a common biological Japanese beetle control option that you could get for relatively cheap at your local garden center. Maybe you've even seen them around your neighborhood in the summertime! They are called yellowfin traps. These traps use sex pheromones that attract adult beetles. They catch about 75% of beetles that approach them. Traps should be placed on the edge of property lines or yard edges to draw beetles away from the lawn.
You can also hand pick Japanese beetles off of your plants as another method to keep their numbers down in your yard. Place them in a bucket of soapy water once you have removed one form a plant. This process is best done early in the morning. They do not sting nor do they bite, so for those who are nervous about that... don't be!
Having another organism that can naturally target whatever species you want to eliminate is a great biological control option. In our case Istocheta aldrichi, aka the winsome fly, is a species of bristle fly that was introduced into the United States in 1922 to combat the Japanese beetle pest problem. They have a four week emergent cycle. They start emerging only a short time before the Japanese beetles. They feed on the flowering nectar. When the japanese beetles emerge as adults from the ground, the females winsome flies then lay their eggs on the back of the beetles thorax, just behind its head. The female fly will lay one hundred eggs over the second two weeks of its four week life emergent cycle. Once the eggs hatch in 24 hours, the larvae will pepetrate the body and feed from the inside out. The Japanese beetles flight muscles are the first to go. In order to protect itself, the beetles drop to the ground and dig their way into the ground where they will die 5-6 days later. The fly larvae stays in the dead beetle all winter until it emerges the following summer and the cycle start over.
Chemical Pest Control Options
There are a bunch of chemicals that you can get at your local garden center to control the japanese beetle populations in your garden. There are some that can target the grub stage of the life cycle and some the target the adult stage. Always try the biological control mechanisms before attempting the chemical control mechanisms.