The Japanese beetle (Popillia japonica) is a common species of beetle. It is about 15 millimetres (0.6 in) long and 10 millimetres (0.4 in) wide, with iridescent copper-colored elytra and green thorax and head. It is not very destructive in Japan, where it is controlled by natural predators, but in North America it is a serious pest of about 200 species of plants, including rose bushes, grapes, hops, canna, crape myrtles, birch trees, linden trees and others.
It is a clumsy flier, dropping several centimeters when it hits a wall. Japanese beetle traps therefore consist of a pair of crossed walls with a bag or plastic container underneath, and are baited with floral scent, pheromone, or both. However, studies conducted at the University of Kentucky and Eastern Illinois University suggest beetles attracted to traps frequently do not end up in the traps, but alight on plants in the vicinity, thus causing more damage along the flight path of the beetles and near the trap than may have occurred if the trap were not present.
These insects damage plants by skeletonizing the foliage, that is, consuming only the leaf material between the veins, and may also feed on fruit on the plants if present.
As the name suggests, the Japanese beetle is native to Japan. The insect was first found in the United States in 1916 in a nursery near Riverton, New Jersey. It is thought the beetle larvae entered the United States in a shipment of iris bulbs prior to 1912, when inspections of commodities entering the country began. "The first Japanese beetle found in Canada was in a tourist's car at Yarmouth, arriving in Nova Scotia by ferry from Maine in 1939. During the same year, three additional adults were captured at Yarmouth and three at Lacolle in southern Quebec."
The life cycle of the Japanese beetle is typically one year in most parts of the United States, but this can be extended in cooler climates; for instance, in its native Japan, the beetle's life cycle is two years long as a result of the higher latitudes of the grasslands required for the larval stage. During the larval stage, the white grubs can be identified by their V-shaped raster pattern.
During the larval stage, the Japanese beetle lives in lawns and other grasslands, where it eats the roots of grasses. During that stage, it is susceptible to a fatal disease called milky spore disease, caused by a bacterium called milky spore, Paenibacillus (formerly Bacillus) popilliae. The USDA developed this biological control and it is commercially available in powder form for application to lawn areas. Standard applications (low density across a broad area) take from one to five years to establish maximal protection against larval survival (depending on climate), expanding through the soil through repeated rounds of infection.
Research performed by many US extension service branches has shown pheromone traps attract more beetles than they catch. Traps are most effective when spread out over an entire community, and downwind and at the borders (i.e., as far away as possible, particularly upwind), of managed property containing plants being protected. Natural repellents include catnip, chives, garlic, and tansy, as well as the remains of dead beetles, but these methods have limited effectiveness. Additionally, when present in small numbers, the beetles may be manually controlled using a soap-water spray mixture, shaking a plant in the morning hours and disposing of the fallen beetles, or simply picking them off attractions such as rose flowers, since the presence of beetles attracts more beetles to that plant.
Several insect predators and parasitoids have been introduced to the United States for biocontrol. Two of them, Istocheta aldrichi and Tiphia vernalis, are well established with significant rates of parasitism.
Japanese beetles feed on a large range of hosts, including leaves of plants of the following common crops: Beans, strawberries, tomatoes, peppers, grapes, hops, roses, cherries, plums, pears, peaches, raspberries, blackberries, corn, peas, birch trees, linden trees, blueberries, and these genera:
- Acer (Maple trees)
- Asimina (pawpaw)
- Cannabis Sativa
- Cirsium (thistle)
- Daucus (carrot)
- Echinacea (coneflower)
- Ilex (holly)
- Ipomoea (morning glory)
- Malus (apple, crabapple)
- Malva (mallow)
- Ocimum (basil)
- Oenothera (evening primrose)
- Platanus (plantain)
- Polygonum (Japanese knotweed)
- Prunus (plum)
- Quercus (oak)
- Ribes (gooseberry, currants, etc.)
- Rubus (raspberry, blackberry, etc.)
- Salix (willows)
- Sambucus (elderberry)
- Solanum (nightshades, including potato, tomato, peppers, eggplant)
- Thuja (arborvitae)
- Tilia (basswood, linden)
- Toxicodendron (poison oak, poison ivy, poison sumac)
- Ulmus (elm)
- Vaccinium (blueberry)
- Vitis (grape)
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- "Japanese Beetles in the Urban Landscape". University of Kentucky. Retrieved 28 September 2015.
- Paul V. Switzer; Patrick C. Enstrom; Carissa A. Schoenick (2009). "Behavioral Explanations Underlying the Lack of Trap Effectiveness for Small-Scale Management of Japanese Beetles.". Journal of Economic Entomology. 102 (3): 934–940. doi:10.1603/029.102.0311.
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