Japanese Beetles
Overview
The Japanese beetle (Popillia japonica Newman) is a destructive exotic pest native to Japan, which currently poses a threat to American shade and fruit trees, shrubs, and turf.
Management of Japanese beetles can be very difficult and costly. It has been estimated that this pest can cost the turf and ornamental industry about $450 million annually in management alone (Potter and Held 2002).
Identification
Adults: They are about 1/3 to 1/2 inch long and have a shiny, metallic-green body and bronze-colored elytra (wing covers). There are six small tufts of white hairs along its side.
Larvae: They have a brown head and grayish-black rear end. They are C-shaped and reach about 1 inch long at maturity. Hairs on the last body segment (raster) have "V" shape pattern just below the anal opening.
Pupae: They are about 1/2 inch long with cream color and become light reddish-brown with age.
Eggs: They are creamy white, oval and about 1/16 inch long when first laid. As the embryo develop, eggs normally enlarge to double their initial size and become almost round.
Biology
Upon emergence, adult Japanese beetles begin to feed and mate for one to two months before dying. Females dig about two inches deep in the soil in nearby turfgrass to lay eggs. Depending on the temperature and moisture content of the soil, eggs hatch in 10 to 12 days and newly hatched grubs move up in the soil to feed on surrounding grass roots and decayed organic matter in the soil. In late fall, when temperatures are below 50°F, grubs move down deep the soil and reside below the frost line for overwintering. In spring, as temperatures rise above 50°F, grubs move up closer to the soil surface to pupate. This usually takes place between late May to June. Adults start emerging in late June to mid-July and repeat the life cycle. In the USA, Japanese beetles have one-year life cycle.
Habits
Unlike May or June beetles, Japanese beetles are most active during the day. However, the adults are known to be less active in the early morning or late evening.
Japanese beetles may lay eggs in different types of soil including, sassafras gravelly sand, loamy sands, sandy loams and peat. However, sandy loams are most attractive to the egg - laying Japanese beetle females (Thomas 1925).
Japanese beetles use their chewing mouthparts to feed on foliage, flowers, or fruits of more than 300 plant species in 79 plant families. Nevertheless, the evergreens as well as many truck crops, field crops, ornamental flowers and grains are considered non-preferred hosts of Japanese beetles. Besides, this pest normally avoids pear trees.
Japanese beetles produce sex and aggregation pheromones. Virgin females emit the sex pheromone to lure males for mating purposes. The aggregation pheromone is used to attract other Japanese beetles to new feeding sources. In addition, males and females aggregate on food plants in response to plant kairomones (kairomones is a chemical produced by an organism that benefits the recipient). This explains why Japanese beetles are normally seen feeding in groups. They usually start at the top of a plant and work their way downward. Adults feed on the upper side of the leaves leaving only the veins and midribs undamaged. This typically gives the leaves a skeletonized appearance. Japanese beetles feed on the low plants in the beginning before they move to feeding on foliage of trees. As aforementioned, larvae feed on surrounding grass roots and decayed organic matter in the soil.
Management
1. Cultural Methods
Handpicking
Handpicking can be used to remove and destroy early scouts of Japanese beetles before they attract other pests. The best time for handpicking is in the early morning or late evening when beetles are less active. This method can be easily done by picking off the beetles and destroying them by dropping them into a container with soapy water. Anyhow, the handpicking method will not provide a satisfactory elimination of Japanese beetles, especially when they are encountered in a big number.
Habitat Modification
In areas commonly infested with Japanese beetles, it is recommended to replace attractive plants to Japanese beetles with non-attractive or non-host ones. Examples of non-attractive plants may include: ash, tulip tree, boxwood, arborvitae, baby's breath, begonia, bleeding heart, buttercups, columbine, catnip, chives, lilacs, tansy, daisies and flowering dogwood.
Trapping
There are various models and types of Japanese beetle traps, which are commercially available for homeowners, researches or farmers to use. Anyhow, trapping Japanese beetles using sex or floral pheromones is not recommend, as this will attract more beetles into the area.
2. Chemical Methods
Timing of the insecticide applications is crucial to managing Japanese beetles. This requires the understanding of the pest life cycle and continuous observation of the weather conditions. When average soil temperatures are hovering above the critical 50°F, the development of the larvae is usually resumed. Therefore, early emergence of the beetles is associated with warmer soil temperatures in early spring.
Both grubs and adults need to be managed. Repeated applications may be also necessary for a 3-year treatment period, especially in areas with a history of Japanese beetle infestations. Preventative treatments of EPA approved insecticides can be done on May, June and early July. To manage adult beetles, treatments to infested foliage should be done on June through August. For grubs control, granular insecticides applied in late summer or fall are usually more effective than spring applications because the grubs are in early instars of development and close to the surface. When soil temperatures drop below 50°F, grubs move deep in the soil and insecticide treatment is not recommend at this point.
References
Potter, D.A. and D.W. Held. 2002. Biology and management of the Japanese beetle. Annual Review of Entomology 47: 175-205.
THOMAS, C. A.1925. Observations on the Life History of Popillia Japonica Newm. Journal of Economic Entomology 18: 357-361
