Popillia japonica, commonly known as the Japanese beetle, is a significant garden and agricultural pest. This invasive species, originally from northern Japan and the far east of Russia, arrived in the United States in New Jersey in 1916, likely through plant material. Without its natural predators, the Japanese beetle has become a widespread threat to various plants across North America and parts of Europe.
Identifying Popillia Japonica
Adult Japanese beetles are easily recognized by their distinct appearance, typically measuring 8 to 12 millimeters. Their bodies feature a metallic emerald green head and thorax, contrasting with coppery-brown wing covers. A distinguishing characteristic is the presence of six small tufts of white, bristle-like hairs along each side of their abdomen, with two additional patches on the tip of their rear end. These white patches help differentiate them from other similar-looking scarab beetles.
The presence of Japanese beetles is often evident through the damage they inflict on plants. Adult beetles consume the tissue between leaf veins, leaving behind a characteristic “skeletonized” or lace-like appearance. They also chew holes in flower petals and fruit. Damaged leaves may turn brown and eventually fall off.
Life Cycle of Popillia Japonica
The Japanese beetle undergoes complete metamorphosis, involving four distinct life stages: egg, larva (grub), pupa, and adult. This entire cycle typically spans about one year. Understanding these stages and their timing is helpful for managing infestations.
Female beetles lay their eggs in the soil, usually between late June and early August, preferring moist, well-irrigated grassy areas. A single female can lay between 40 to 60 eggs during her adult lifespan, depositing them about 2 to 4 inches deep. After approximately two weeks, these eggs hatch into small, C-shaped, creamy white larvae, commonly known as grubs.
These grubs remain in the soil, feeding on plant roots and decaying organic matter throughout late summer and fall, typically at depths of 2 to 4 inches. As temperatures drop in late autumn, they burrow deeper, often 4 to 8 inches, to overwinter. In the spring, as soil temperatures rise, the grubs move closer to the surface to resume feeding before transforming into the pupal stage. The pupal stage lasts about two to three weeks, during which the grubs develop into adult beetles, emerging from the ground from late May to early June.
Damage Caused by Popillia Japonica
Adult Japanese beetles are known to feed on over 300 different species of plants, including fruit trees, ornamental trees, shrubs, vines, and various field and vegetable crops. Their feeding habits lead to skeletonized leaves, where only the veins remain, and they also consume flowers and fruits, leaving irregular holes. Roses, grapes, linden, apple, crabapple, cherry, and elm are among their preferred host plants.
The larval stage, or grubs, primarily damages turfgrass by feeding on its roots. This root feeding reduces the grass’s ability to absorb water and nutrients, leading to brown, dead patches in lawns that can be easily pulled back like a loose carpet due to the compromised root system. Severe grub infestations can also attract animals like moles, skunks, and crows, which dig up the turf in search of the grubs.
Managing Popillia Japonica Infestations
Managing Japanese beetle infestations involves a combination of strategies to address both adult beetles and their grubs.
Manual Removal
Adult beetles can be hand-picked from plants in the early morning when they are less active and dropped into a bucket of soapy water. This method is most effective for smaller infestations or prized plants.
Cultural Practices
Maintaining healthy, vigorous plants through proper watering and fertilization can help them tolerate some feeding damage. For lawns, minimizing irrigation during the beetle’s egg-laying period in mid-summer can make the soil less attractive for egg deposition.
Biological Controls
Beneficial nematodes, such as Heterorhabditis bacteriophora and Steinernema feltiae, are microscopic parasitic roundworms that actively seek out and infect grubs in the soil, causing their demise. These nematodes are typically applied to the soil when grubs are present. Additionally, certain predatory insects, like the parasitic wasp Tiphia vernalis, target Japanese beetle grubs by laying eggs on them, with the hatching wasp larva then consuming the grub.
Physical Barriers
Using netting or row covers can prevent adult beetles from accessing and feeding on susceptible plants.
Chemical Controls
Insecticides can be applied to foliage to target adult beetles or as soil treatments to control grubs. It is important to follow product label instructions precisely for application rates and timing to ensure effectiveness and minimize environmental impact. Combining these various methods, known as Integrated Pest Management (IPM), offers a comprehensive and sustainable approach to keeping Japanese beetle populations below damaging levels.