The Japanese beetle and similar species live in grass turf, eating other insects. Unfortunately, their larval grubs prefer to feast on grass roots. Given that a single pair of beetles can produce up to 60 eggs in the summer breeding season, this represents significant lawn damage. Between 10 and 20 percent of yards are infested with white grubs, and though most yards can withstand about 10 grubs for every square foot of turf, those with serious infestations will die without your intervention.
As white grubs do not have chewing mouth parts, but instead pierce grass roots and suck the moisture from them, a pesticide which is designed for insects to eat is ineffective. Merit is the brand name of imidacloprid, a pesticide which you sprinkle on the surface of the lawn in early summer, when grubs begin to hatch and feed. It is absorbed by the grass and carried down to the roots, where the grubs eat it and die. Mach 2 is the brand name for halofenozide, which is introduced by similar means, but rather than being a poison, is an artificial hormone. When grubs ingest this hormone, it forces them to go through molting prematurely, which is lethal, but harmless to insects beneficial to your lawn.
Bacillus popilliae Dutky, a bacterium more commonly known as milky spore disease, is a new method by which lawn grubs can be destroyed. Initial research by the University of Rhode Island has shown mildly satisfactory results. Once the spores are released in the lawn, they infect the initial generation of grubs, which sicken and die off. Over the course of the year, the bacteria propagates and increases in number so that it will attack and kill the next generation of grubs more quickly, and so on until the lawn is free of grubs entirely. Nematodes are a phylum of roundworms. The species Heterorhabditis bacteriophora has shown itself to be entomopathogenic, they act as fatal parasites to insects. Organic white grub treatments containing these nematodes are available. As long as they have a wet, well-watered environment to live in, they will kill of white grubs and then die when there are no more insects to eat.
Neem oil is extracted from the neem, an evergreen tree native to India. It is extremely bitter, smells strongly of garlic and peanuts, and acts as an insect repellent. Japanese beetles find the weak acids present in neem oil to be unpalatable and will leave any part of the lawn containing it. The effect is twofold in the case of larval white grubs. Should any Japanese beetles have laid eggs before the oil's application, those eggs will hatch as usual. But the thin skin of the grubs will sustain burns on contact with neem oil, which are eventually fatal.