By Francesco Pacelli,
Nursery Technical Analyst

The Japanese beetle, Popillia japonica (Newman), is a widespread and destructive pest of turf, landscape and ornamental plants. It is also a pest of several fruit, garden and field crops, with a total host range of more than 300 plant species. Adult Japanese beetles feed on foliage, flowers and fruits. Leaves are typically skeletonized, or left with only a tough network of veins. The larvae, commonly called white grubs, primarily feed on roots of grasses, often destroying turf in lawns, parks and golf courses.
 

Adult

The adult is an attractive and broadly oval beetle, 8 to 11 mm long and 5 to 7 mm wide. It is generally metallic green, with bronze or coppery-brown elytra that do not completely cover the abdomen. The five patches of white hairs on each side of the abdomen and one pair on the last abdominal segment distinguish P. japonica from all other similar looking beetles.
 

Egg

Newly deposited eggs may be spherical, ellipsoidal or slightly cylindrical and usually have a diameter of about 1.5 mm. It may be translucent to creamy white with small hexagonal areas on the surface. During embryo development, the egg enlarges to double its initial size and becomes almost spherical.
 

Larva

Translucent and creamy white, the grub is covered with scattered long brown hairs, interspersed with short, blunt spines. The head is yellowish-brown with strong dark-coloured mandibles and the body consists of three thoracic and ten abdominal segments. Each thoracic segment bears a pair of segmented legs. As typical of a scarab larva, the grub is ‘C’-shaped when at rest. It can be identified by examining the arrangement of the spines on the underside of the last abdominal segment called the raster. The spines of Japanese beetle form a ‘V’ shape.
 

Pupa

Pupation takes place within an earthen cell formed by the last larval instar, and is about 14 mm long and 7 mm wide. Its colour ranges from pale cream to metallic green, depending upon the age.
 

Lifecycle

The Japanese beetle completes its lifecycle in one year. Males emerge a few days earlier than females, but eventually the population maintains a sex ratio of 1:1 (Fleming 1972, Régnière et al. 1981). Mating begins soon after emergence, as virgin females release powerful sex pheromones that immediately attract large number of males. In an attempt to mate, the attracted males form a congregation around the unmated female, forming clusters referred to as beetle balls. Mating rarely occurs under such intense competition (Ladd 1970).

Selection of a site for oviposition is influenced by proximity to host plant, nature of ground cover and the soil condition. Although Popillia japonica generally lays most of its eggs on pastures, lawns and golf courses, eggs may also be deposited in agricultural fields. During dry summers, when pastures are hard and dry, beetles are known to seek cultivated and fallow fields with loose and moist soil. The ovipositing female burrows into the soil at a depth of two to four inches and deposits one to three eggs (singly). Eggs hatch in 10 to 14 days. The first instar feeds on nearby rootlets and organic matter for two to three weeks and molts for the first time. The second instar continues to feed for another three to four weeks and molts to a third instar. The majority of grubs reach the third instar by the fall when soil temperature gradually decreases. The activity of the grub ceases around 10°C (50°F) and most larvae overwinter as third instar at a depth of five to 15 cm (two to six inches). With the beginning of spring, the grubs return to the plant roots to resume feeding for four to six weeks, until they are ready to pupate. Pupation usually occurs near the soil surface, and takes one to three weeks. Adults emerge from late June through mid-July.
 

Hosts

More than 300 species of plants are known to host the Japanese beetle. The following are some of the better-known primary and secondary hosts (CABI 2004).

Primary hosts: Acer (maples), Asparagus officinalis (asparagus), Glycine max (soybean), Malus (ornamental species apple), Prunus (stone fruit including plums, peaches etc), Rheum hybridum (rhubarb), Rosa (roses), Rubus (blackberry, raspberry), Tilia (limes), Ulmus (elms), Vitis (grapes), Zea mays (corn).

Secondary hosts: Aesculus (buckeyes), Althaea (hollyhocks), Betula (birches), Castanea (chestnuts), Hibiscus (rosemallows), Juglans nigra (American walnut), Platanus (planes), Populus (poplars), Salix (willow), Sassafras albidum (common sassafras), Sorbus americana (American mountain ash), turf grasses.
 

Damage

Both adults and larvae cause plant damage, but the host and nature of damage are usually different. Adults cause damage on foliage and flowers of a wide range of hosts and are most active on warm sunny days. The grubs primarily feed on roots of grasses. Feeding damage on roots reduces the ability of grass to take up enough water to withstand stresses of hot and dry weather, resulting in dead patches.
 

Management

Attractants and trapping: Commercially available Japanese beetle traps are useful in reducing small, recently established, or isolated populations. However, the correct placement is important, as lures and traps placed adjacent to host plants attract more beetles and result in heavier damage (Gordon and Potter 1985). Even though these devices are most useful for monitoring populations and detecting new infestations, the deployment for mass trapping to suppress established populations is considered rather ineffective (Potter and Held 2002). Traps should be placed in late June to mid-September.

Cultural control: During dry summers, female beetles seek irrigated and low lying areas for oviposition, since soil moisture is essential for egg survival and larval development. Withholding of irrigation during peak beetle flight activity may reduce grub population in turf (Potter et al. 1996). Clean cultivating soils may also discourage females to lay eggs.

Biological control: Two species of tiphid wasps, Tiphia vernalis Rohwer and Tiphia popilliavora Rohwer, have proven successful biocontrol agents against Japanese beetles grubs (Fleming 1976). T. vernalis attacks overwintering grubs, whereas T. popilliavora attacks young grubs in late summer. A tachinid fly, Istocheta aldrichi (Mesnil), parasitizes adult Japanese beetles (used in U.S.). Ants and ground beetles feed on eggs and young larvae; moles, skunks, and racoon also prey on the grubs, although their foraging activity may often be destructive to turf (Potter 1998). An entomopathogenic nematode, Steinernema kushidai (Mamiya), has been observed to cause mortality rates comparable to an organophosphate insecticide, diazinon (Koppenhöfer et al. 2000). It is specific to scarab larvae and has lasted in the field for one to two years. Its use, in combination with other chemical products, is known to produce a synergistic effect. Two other nematodes, known to be most effective against Japanese beetle grubs, are Steinernema glaseri (Steiner) and Heterorhabditis bacteriophora (Poinar). Dusts containing spores of Bacillus popilliae (Dutky), the causal agent of milky disease, have been used in the past with satisfactory results, but isolate of Bacillus thuringiensis, designated as serovar japonensis strain Buibui (Btj), has subsequently been found to be more effective (Potter and Held 2002). This bacteria is not registered in Canada.

Chemical control: Organophosphates (Imidan 50 WP) and carbamate (Sevin XLR plus).
 

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Francesco Pacelli may be reached at fpacelli@landscapeontario.com.

Captions:
Popillia japonica larva
Popillia japonica adult
Popillia japonica