The beetle species Popillia japonica is native to Japan and is commonly known as the Japanese beetle. In its native land, it is not very destructive because of the presence of natural predators but in America it is a troublesome pest of over 200 species of plants and trees.
In a way, Japanese beetle infestations do twice the damage of ordinary insect pests. The adult beetles feed on the foliage, flowers and even overripe/wounded fruits while their larvae live in the soil and feed on grasses and roots of plants. Hence controlling Japanese beetles requires a two-pronged attack- one for the beetles above the soil and one for the grubs underneath!
Japanese beetles are strangely beautiful to look at.
Adults are roughly 1/2 inch long and 1/4 inch wide, with iridescent metallic-green bodies, copper-colored wing covers and a row of five tufts of white hair on each side of the abdomen which help identify them from other similar looking beetles.
Adults emerge from the ground after overwintering in the soil and begin feeding. Females lay eggs 2-4 inches in the soil, preferring moist warm areas. Eggs are small, translucent to creamy white and hatch in 8 to 14 days. The larvae are C-shaped, creamy white with a brown head capsule and about an inch long. The grubs complete their 3 stages in the soil and spend about 10 months in the soil before they pupate into adult beetles.
The Japanese beetles attract other beetles of their kind by releasing a chemical called pheromone in the air. This makes them a painstakingly irritating bug to deal with as they feed in groups and their numbers just seem to be on the rise all the time.
Adult Japanese beetles usually feed in groups, starting at the top of a plant and working downward. They eat flowers and skeletonize leaves of a wide range of plants, vegetable crops and trees, including roses, fruit trees, grapes, beans, tomatoes, corn, soybean and most landscape plants. Larvae mainly feed on roots of lawn grasses and other garden plants.
Organic Control of Adult Japanese Beetles:
Handpick: Japanese beetles are slow and can be easily picked off plants. Startle them in the morning or late evening when they are least alert by
shaking infested plants and drop them into a bucket of soapy water.
Plant Trap Plants: Interplant four o’clocks (Mirabilis), larkspur, white geraniums, and red (and dwarf) buckeyes in your garden. The flowers of these plants attract and poison the beetles. The leaves of the castor bean plant are poisonous to Japanese beetles. Care must be taken though, since these plants are poisonous to people too.
Plant Non-Attractive Plants: The adults do not like feeding on ageratum, ash, balsam, begonia, boxwood, carnations, firs, hemlock, holly, junipers, lilac, magnolia, oaks, pines, redbud, red maple, rhododendrons among plenty others. Deter them by planting these all over your garden.
Plant Natural Repellants: Catnip, chives, garlic and tansy are natural Japanese beetle repellants but have only a limited effectiveness.
Row Covers: Cover susceptible plants with floating row covers to prevent adult beetles from feasting on foliage. Make sure to fasten the edges to the ground so that stubborn beetles do not crawl through.
Neem Oil: Neem oil acts as an anti-feeding agent and is approved for organic gardens. Works great when used on early infestation detection. Try an organic insecticidal soap as they can help in minimizing beetle damage.
Traps: There are several traps available that use a floral lure and the sex attractant pheromone to trap adult Japanese beetles. Traps are not recommended though for home gardeners, since research shows that the trap attracts more beetles than they catch. However, traps can be effective when spread out over an entire community and at the borders, away from plants that need protection.
Biological Control: The anchor bug and blue-winged wasp are natural predators of the Japanese beetles. Chickens and birds feed on Japanese beetles, so let them loose in your yard if possible.
Organic Control of Japanese Beetle Grubs
Milky Spore Disease: Milky spore (Paenibacillus popilliae) is a naturally occurring bacterium can be used to rid of the grubs in the soil as an effective long term control. The grub ingests these bacterial spores, which germinate and multiply in the grub’s body, ultimately killing it.
Btj: Bacillus thuringiensis japonensis is another naturally occurring bacterium that can be used to destroy Japanese beetle grubs. The grub ingests the Btj which attacks its digestive system, eventually killing it.
Nematodes: Heterorhabditis bacteriophora is a beneficial nematode that works to control Japanese beetle grubs. These microscopic parasitic roundworms penetrate grubs and inoculate it with bacteria that grow rapidly in the grub’s body. The nematode feeds on the bacteria and this leads to the demise of the grub.