Japanese Beetles

Japanese Beetles (Popillia japonica) are a highly destructive and invasive pest, both in the adult and larva stages. The larvae, are white grubs that feed on the roots of mainly grasses. While the adults feed on the leaves of over 300 types of plants, skeletonizing them. The adults are able to fly up to 8 km (5 miles) with a good wind, in search of food or mates and have a tendency to congregate. On mass they they can strip a tree or plant bare in very short time. They are native to Japan and first arrived in USA in 1916 and Canada in 1939 (Gov. of Canada, (rev. 2017-08-16)). In Canada they are reported in Ontario, New Brunswick, Nova Scotia, Prince Edward Island and Quebec (Gov. of Canada, (rev. 2017-08-16)).

An adult Japanese beetle. Photo by
Kimberley Pacholko.

Meet the Pest

Adults are scarab beetles that have hard exoskeletons. They have a metallic green head and thorax with metallic copper wing cases (elyptra), black legs and tufts of white hair along either side of their abdomen. They can grow to about 15mm in length. They are often observed mating and several beetles will congregate on one leaf.

Larvae “are C-shaped, milky-white grubs about 20- 25 mm. They have brown heads and three pairs of legs. A V-shaped arrangement of spines on the last abdominal segment (raster) distinguishes them from other grubs” (OMAFRA,. (2014)).

Pupae: Light reddish brown, 13 mm long and 6 mm wide.

Eggs are globular in shape and fairly transparent, measuring about 2mm. They hatch in about 10 days. Each female beetle can lay up to 60 eggs in their life span.

Damage Caused by Japanese Beetles

Japanese beetle adults feed on more than 300 types of plants. They skeletonize leaves, feeding on the upper leaf surfaces between the veins, creating a lacy pattern that turns brown. They feed in groups or masses and can do extensive damage in a short amount of time. They also feed on flowers and fruit.

Japanese beetle grubs feed mainly on the roots of grasses from April to the end of May and again from August to November. With little to no roots the grass easily pulls up like a carpet and turns brown. It is most noticeable in the fall. Secondary damage occurs when skunks, raccoons and birds dig up the turf in search of the grubs to eat.

Adult beetles feed on more than 300 types of plants. Below is a partial list. For a more complete list visit The Gov. of Ontario’s website

  • Rosebushes (Rosa)
  • Rose of Sharon (Hibiscus syriacus)
  • Climbing hydrangeas (Hydrangea petiolaris)
  • Virginia creeper vine (Parthenocissus quinquefolia)
  • Rose mallow known as hardy hibiscus (Hibiscus moscheutos)
  • Potentilla (Cinquefoil)
  • Purple leaf sand cherry (Prunus × cistena)
  • Grapes (Vitis spp.)
  • Raspberry (Rubus spp.)
  • Hops (Humulus lupulus)
  • Coneflowers (Echinacea)
  • Gladiolus
  • Shasta daisies (Leucanthemum × superbum)
  • Hollyhocks (Alcea)
  • Zinnia
  • Canna lilies (Canna)
  • Sweet potato vine (Ipomoea batatas)
  • Japanese Maples (Acer palmatum)
  • Maples (Acer spp.)
  • Linden trees (Tilia)
  • Crabapple trees (Malus spp.)
  • Birches (Betula)
  • Cherry trees (Prunus spp.)
  • Willow trees (Salix spp.)

Life Cycle

Japanese beetles overwinter in the soil as a 3rd instar larvae at a depth of about 15-30cm (6-12″). When the soil temperatures begin to warm up in the spring (usually April and May) the larvae move up to about 5-10cm from the soil surface (if there is adequate moisture), and resume feeding on the roots of grasses or sometimes crops. In June sometime, the larvae stop feeding and pupate. The adults begin emerging from the pupae in about July feeding on the leaves, flowers and fruit of a wide variety of plants for about 30-45 days. During this time the adults are also mating. Eggs are laid in the soil and require adequate moisture to properly hatch and develop. The eggs hatch in about 2 weeks and the 1st instar larvae and then the second and 3rd feed on the roots of grasses and sometimes crops, until the soil temperatures begin to cool again. At that point the 3rd star larvae begin moving down the soil profile (around Oct.) where they will over winter. There is only one generation per year.

The adult beetles prefer sunny locations and do the bulk of their feeding and mating during the morning and early afternoon then return to the soil in the late afternoon and evening.

Control and Management of Japanese Beetles

Properly Identify Your Insect Pest: Japanese beetles are often confused with June Beetles and Rose Chafers. While the beetles clearly look different from one another the grubs are difficult to tell apart, and since they have a different life cycle proper identification is an important first step.

Choose resistant plants: Japanese beetle adults usually will not bother Ash, Boxwood, Burning bush, Clematis, Fir, Forsythia, Hemlock, Holly, Lilac and Magnolias. Grubs on the other hand do not like alfalfa, barley, buckwheat, clover (white, red, or alsike), common rye, oats and orchard grass.

Cultural practices:

  • Keep plants well watered, fertilized and other wise healthy, so they can with stand some feeding damage.
  • Keep the soil on the dryer side during egg laying and development.

Physical controls:

  • Hand picking works well when the numbers are not high. Tap the beetles off the plant into a bucket of warm soapy water then flush down the toilet.
  • Hoop Houses with shade cloth over them during the flight time of the beetles will help to protect plants.
  • Keep area free of weeds. Many weeds attract Japanese beetles.
  • Cultivate in late spring and early fall to help control larvae.

Predators:

  • Some birds will eat both the adults and the larvae such as crows, cardinals, grackles and starlings.
  • Some insects and spiders feed on larvae.
  • Some mammals such as skunks, racoons, moles and opossums will feed on grubs.

Trap plants: Certain plants such as Geraniums, castor bean, and the flowers of the bottlebrush buckeye contain a chemical that temporarily paralyzes Japanese beetles, rendering them vulnerable to predators.

Traps: traps that use favourite plants scents and or pheromone scents, are available. If you opt for one be sure to place it at least 9meters (30′) away of vulnerable plants further if possible. If you are on an acreage or large property 76 meters (250′) is ideal. Place them in a non-flowering tree, like a pine or spruce about 4′ high. Note: these traps will lure about 4 times as many Japanese beetles to your yard then you would normally have; they trap about 75% of those lured…meaning you have not in the end really reduced their numbers.

Biological controls:

  • Nematodes are microscopic like worms that parasitize the grubs. They need to to be reapplied each time and require adequate moisture both before and after application to prevent drying out and dying. Soil temperatures must also remain above 11°C. Apply when grubs are young and actively feeding near the soil surface in late July to mid-September.
  • Milky spore disease, Bacillus popilliae, is a naturally occurring bacteria. This bacteria is not registered in Canada.

Natural and low impact sprays: apply sprays early in the morning after the beetles come out of the soil and are still sluggish. Optimal flight temperature is 21°C.

  • Neem oil: comes from the neem tree in India. When sprayed on the beetle it causes them to stop feeding and makes them unable to reproduce.
  • Pyrethrin: is a natural ingredient from chrysanthemums and is considered safe to use on even food crops. Pyrethrin interferes with the insects nervous system.

Chemical controls: apply insecticides early in the morning after the beetles come out of the soil and are still sluggish. Optimal flight temperature is 21°C. Only use chemicals that are approved of for use against Japanese beetles, in your area, as a last resort. Current recommended chemical control may be found in OMAFRA Publication 840 Crop Protection Guide for Nursery and Landscape Plants and Publication 384, Recommendations for Turfgrass Management.

Photo credits: All photos by the author.

References:

Gaeng J (2021). How to Get Rid of Japanese Beetles. https://a-z-animals.com/blog/how-to-get-rid-of-japanese-beetles/

Hahn J., Weisenhorn J., and Bugeja S., (rev. 2020). Japanese beetles in yards and gardens. https://extension.umn.edu/yard-and-garden-insects/japanese-beetles?msclkid=1e3cdd58c00d11ec98d7a2f36012bfef

Kessel C., (1992, rev. Feb. 12, 2021) Japanese Beetles in Nursery and Turf. MINISTRY OF AGRICULTURE, FOOD AND RURAL AFFAIRS. http://www.omafra.gov.on.ca/english/crops/facts/92-105.htm

Maine Gov., (2005). White Grubs. https://www.maine.gov/dacf/php/gotpests/bugs/grubs.htm

Nixon P. and Cloyd R.A., (2003). Japanese Beetles: impact of Winter. http://hyg.ipm.illinois.edu/pastpest/200315f.html

OMAFRA,. (2014) Guide to Nursery and Landscape Plant Production and IPM pg. 35, Retrieved from: Publication 841, Guide to Nursery and Landscape Plant Production and IPM (gov.on.ca)

Gov. of Canada, (rev. 2017-08-16). Popillia Japonica (Japanese Beetle) – Fact Sheet. https://inspection.canada.ca/plant-health/invasive-species/insects/japanese-beetle/fact-sheet/eng/1328165101975/1328165185309

Smitley D. , (2017). Japanese beetle: Tips for your lawn. https://www.canr.msu.edu/resources/japanese_beetle_tips_for_your_lawn

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