Whenever I think of Japanese beetles – Popillia japonica Newman — images from the movie Starship Troopers (1997) come to mind. The parallels are not on target: we are not explicitly at war with these “bugs” – they don’t fight with humans — but I can’t help it.
You Know Something’s Bad When So Much is Written About It
Since their appearance on our lands, these little creatures have caused significant economic expenditures and, especially among some gardeners not to mention farmers, emotional pain. We wage war against them as individuals and as a nation. The importance of the challenge is evident in the volume of excellent literature available that instructs us in how to control them. It seems that every cooperative extension organization, especially from the east coast to the Midwest, as well as the federal government has something to say. If you are a gardener and facing a beetle invasion and need some quick and direct guidance, begin with the Animal and Plant Health Inspection Service’s (United States Department of Agriculture) Managing the Japanese Beetle: A Homeowner’s Handbook and Virginia Cooperative Extension’s Home Grounds & Animals: 2023 Pest Management Guide (for pesticide application). For a condensed overview see Japanese Beetle (especially useful for guidance on types of chemical application) by Theresa A. Dellinger, Eric Day, Alejandro DelPozo, and Doug Pfeiffer, Virginia Cooperative Extension and The Japanese Beetle Popillia japonica Newman (Scarabaeidea: Coleoptera) by Gale R. Ridge, The Connecticut Agricultural Experiment Station, which complements it. There are some very good videos too; see especially Japanese Beetles by Dr. Donald Lewis, Iowa State University Extension and Outreach. (These are also the sources from which most of what follows was derived.) Below, I do not replicate or retell the bulk of what is in these and other listed resources. If you find what appears to be a vital or obvious piece of information missing, please consult one or all of the above sources as well as some of those listed at the end of this discussion.
A Beetle’s Life
From egg to larva (white grub) to pupa to adult beetle, the life cycle of the Japanese beetle is an example of complete metamorphosis. Depending on your perspective, it’s a beautiful process. The stages of development present their own horticultural challenges. The life cycle is annual, although there can be some exceptions. The terminal form, the adult beetle, lives for only about 2 months. Prior to this, in late June to mid-July the adults emerge in waves, not all at once. The female is a little larger than the male (otherwise they look alike, except the female has an elongated spur on the fore tibia). The females emit pheromones to attract mates, and they mate (with multiple partners) and feed intermittently. Mated females intermittently dig small burrows in the soil and lay eggs from mid-July through mid-August. Feeding and mating is vigorous. In their world of intense scents, adult beetles swarm, sometimes on only a targeted portion of a plant.
They rest at night and are most active during the day. They like sunny weather, warm temperatures, and still air. Energy and time are at a premium. Adult beetles devour the tissue on a leaf’s upper surface between the veins, skeletonizing them in a lace-like pattern.. They generally attack a plant from the top down and feed on buds, flowers, fruits, and leaves. The remains of leaves turn brown presenting an image of gloom and doom, death and despair. Most healthy plants will weather the onslaught. Once the beetles retreat, new leaves and flowers will be grown. Ultimately, they will deposit 40-60 eggs, although only 4 eggs will be laid at a time. In 8-9 days, eggs hatch, but require moist soil to develop. If drought conditions prevail, their numbers are depleted and the following year will exhibit a decrease in adult beetles. In fact, if breaking the beetle cycle is a goal, consider watering less often in hot weather. Of course, beetles can fly in from elsewhere, so this may not have the impact desired. Ironically, an irrigated and well-fed lawn can be their best nursery. The young grubs (the larva stage) gorge themselves on rootlets of increasing diameter until fall brings cooling soil. They then burrow down between 4 and 8 inches. Spring brings increasingly warm soil and they travel upward and begin feeding again. Between May and early June, the grubs mature and pupate. This is the stage between larva and adult. The emergence of adults occurs some weeks later. The cycle completed, a new one begins with the depositing of eggs.
Japanese beetle grubs (larva) probably entered the United States in 1916 arriving at a nursery near Riverton, New Jersey, presumably in imported rhizomes of the Japanese iris. Today considerable effort is made to prevent their transport by aircraft from the eastern to the western states, where they would endanger agriculture and natural resources. At first, they were isolated in southern New Jersey. Although originating in Japan, the island’s climate and predators were not conducive to their spread. This was not the case in America. Fortunately, mountains stopped them and topography, temperature, rainfall, and even winds can be factors. Early infestations were in Pennsylvania in
1920, New York in 1932, Massachusetts in 1942, and North Carolina and Ohio in 1952. They appeared in Nova Scotia in 1939. Infestations were recorded in Virginia in 1941. Today Japanese beetles are established in 28 states and 5 Canadian provinces and partially established in 6 states. Their spread is analogous to an invasion – and after all, that’s what invasive species are, invaders – and this occurred at a time of heightened anti-Asian passions and opposition to Asian immigrants and Americans of Asian descent. Regrettably, references were made to the “Jap beetle.”
What’s on the Menu?
Japanese beetles voraciously attack vegetable crops, the leaves of various trees, fruit trees and fruit, buds, flowers, shrubs ,and grass roots. Commercial crops and ornamental plants suffer. It is safe to say that over 300 plants are vulnerable, although one source suggests 435. Some of the most heavily damaged species include Japanese maple, asparagus, raspberry, soybean, crab apple, apple, apricot, plum, sweet cherry, sour cherry, peach, nectarine, poison ivy, roses, American linden, American and English elm, sassafras, grapes, and corn. One can readily see why lawns and roses are only a small part of the horticultural nightmare.
Control
A gardener’s responses can take various forms, and nature responds as well. Birds and skunks, opossums, raccoons, shrews, and moles try to help (themselves), but the number of beetles and grubs is simply too large for them to turn the tide. Starlings and grackles eat larvae and adults; meadowlarks, cardinals and catbirds eat adult beetles; and crows and gulls eat beetles as do chickens and ducks. If you repeatedly see these animals on the same part of your lawn, it may signal a grub problem. The female wasp Tiphia vernalis digs into the ground, where she finds a grub, paralyzes it, and deposits an egg, which hatches, eating the grub. Adult beetles are attacked by the fly parasite Istocheta aldrichi in the Northeast. In two weeks, the female fly can lay as many as 100 eggs on a female beetle’s thorax. Hatched maggots drill into the adult beetle killing her. In addition to these seemingly specialized insects, spiders, assassin bugs, praying mantises, and predatory stink bugs dine on beetles and grubs.
Some plants, of course, are not susceptible to Japanese beetle damage. These include the shrubs forsythia, hydrangea, juniper, holly, lilac and yew; the perennials columbine, foxglove, lily and poppy; and the trees fir, red maple, silver maple, white ash, tulip tree, magnolia, pine and arborvitae. These plants are not attractive to Japanese beetles. Also, grow susceptible plants away from turf (the place grubs call home), thus possibly challenging an easy replay of the beetle’s life cycle at that location. What are Japanese beetles good for? Well, as noted above, they are a snack or meal for some animals. Incidentally, there is literature on human consumption of Japanese beetles — definitely not a recommendation — see Put the Bite on Bugs by the Maine Organic Farmers and Gardeners Association.
To be effectively controlled or even eliminated, a Japanese beetle infestation ideally should be addressed at all of the beetle’s life stages. Responses can be mechanical or include biological warfare, chemical warfare, trickery, or the introduction of assassins. A response may include one or more of these approaches. An Integrated Pest Management (IPM) approach seeks to control the problem, but not cause unpredictable collateral environmental damage — killing bees and other beneficial insects in an ultimately doomed attempt to eradicate the beetle with a chemical onslaught. Beware of unintended consequences; scientists continue to discover them. For instance, under certain conditions blue orchard mason bee populations can be seriously impacted by soil-based exposure to imidacloprid, a systemic preventive. These wild bees are prodigious pollinators. In general, across the spectrum of chemicals treatments, if one insect species is affected, it is unlikely that under certain conditions and toxicity levels, others are not as well. Monitor your property and be mindful that pesticides are both dangerous and expensive. Remember, your yard is not a multi-million dollar agricultural enterprise. For now — anyway — Japanese beetles are here to stay.
Mechanical Approach: If you have only a few beetles in a very contained area, try removing them by hand and dropping them in a jar of soapy water. Soapy water will suffocate the beetle. If the beetle who landed on your plant was a “stray,” this may solve the problem. Alternatively, you can spray the infested plant with a soapy-water solution to provide temporary protection against adults. Morning or evening is best for this approach — this is when they are still or least active.
Trickery: This is actually a combination of approaches, but the goal is to make the beetle think it is flying into a good place – not into entrapment and eventual death. Japanese beetle traps (yellow fins with a suspended bag), unfortunately, can play a trick on you. They work as a lure and can bring beetles to your property who might otherwise have flown by. They use sex pheromones or floral scents or their combination. The beetle’s two weaknesses are food and lust. Traps may ensnare about 75% of beetles that fly by them; however, there is controversy about the advisability of their use. The Virginia Department of Forestry (Tree and Forest Health Guide) advises: “Pheromone traps are not recommended because they attract large populations of beetles and could increase damage levels instead of reducing them.” In fact, more beetles may be attracted than the trap can hold. While Japanese beetles are said to be weak and clumsy fliers, to travel a couple of miles at once is normal, and 10 to 15 miles from the place of their grub-life is possible. Place traps as far away from target area – your yard – as possible and deploy them June through late August or during the mating season. Empty into a pail of soapy water daily. Traps are most effective when used is cooperation and coordination with neighbors. The impact they will have on next year’s brood, however, is highly uncertain. Although emotionally rewarding, the general use of traps is not recommended by experts.
Biological Warfare: Although once again not a good parallel, this sort of reminds me of H.G. Wells’ The War of the Worlds (1895-1897). The approach here is to give only beetles a deadly disease. This is a longer term approach. Milky spore disease — Paenibacillus popilliae, formerly Bacillus popilliae Dutky — needs time to build up in the soil to lethal levels. Grubs ingest the spores, die, and more spores are dispersed into the surrounding soil by their carcasses. The spores persist for 2-10 years and in a treated area perhaps as long as 30 years. Refrain from insecticide application for grubs if pursuing this course. Bacillus thuringiensis (Bt), another bacteria species, can be used at the grub stage, but also affects adults. It too is safe for mammals, and has very little toxicity to bees. It takes only minutes after its consumption for an insect to cease feeding. Efficacy, however, may be inconsistent.
Hired Assassins: This approach requires the introduction of hired killers in the form of organisms that prey on Japanese beetles. The entomopathogenic nematodes (Steinernema carpocapsae and Heterorhabditis bacteriophora) attack white grubs. The former targets insects near the soil’s surface, and the latter searches for insect larva deeper in the soil. They burrow into a grub and release a bacterium, which kills it. Unfortunately, scientific study shows that they kill bees exposed to soil containing them. These nematodes can be purchased as a mix; apply with a watering can or sprayer.
Chemical Warfare Against Adults (some are the so-called Nuclear Option): Toxicity levels have been checked in the 2023 Pest Management Guide. I have also consulted The Connecticut Agricultural Experiment Station’s The Japanese Beetle and Virginia Cooperative Extension’s Japanese Beetle. When considering an application, check the Pest Management Guide and read the product’s label very carefully. Do not violate the label’s stipulations or applicable laws. For elaboration as well as other options: see the insecticide list in Managing the Japanese Beetle: A Homeowner’s Handbook, review Clemson Cooperative Extension’s White Grub Management in Turfgrass (for grubs and mentioned again below), consider visiting a trusted garden shop, or call or visit a Virginia Cooperative Extension help desk (Piedmont Master Gardeners). For a list of certified Virginia pesticide applicators visit the website of the Virginia Department of Agriculture and Consumer Services.
While highly effective, Carbaryl (brand name Sevin, a contact insecticide) is highly toxic to bees, extremely toxic to earthworms, and a moderate hazard to humans and mammals. Pyrethrins have become a favorite. They are toxic to the insect nervous system. Toxicity is generally low for humans and other animals, but they are highly toxic to honey bees. Rotenone is derived from plants, but is highly toxic to fish and some species of birds, but is considered relatively nontoxic to honey bees and is safest when applied in the evening or early morning. Azadirachtin is also a botanical insecticide, derived from Neem, and is relatively nontoxic to honey bees and is safest when applied evening and early morning. It repels insects, acts as a direct toxin, and inhibits growth and reproduction. Neem oil can kill by suffocation on direct contact, especially on soft bodied insects, but this is not a likely consequence of its use on adult beetles. The ingestion of treated material, depending on the product’s formulation, reduces feeding and inhibits growth and reproduction, but it is most effective as a temporary deterrent. It poses a low risk for beneficial insects and might be a first response for low density infestations, but requires repeat application. Imidacloprid, discussed below, can be applied to foliage, but is usually applied to the soil.
It’s All About the Lawn: More chemical warfare! This is about destroying them while they’re young, before they grow up and become even more destructive. At this point, they are just wrecking the grass! They feast primarily on grass roots, but also on other tender roots. Home lawns are generally not so severely impacted that treatment is mandatory; however, grubs do grow up to become beetles. White Grub Management in Turfgrass by Clemson University Cooperative Extension is an overall excellent piece and offers detailed guidance on insecticide application. It gives brand and product, active ingredients, and form, sizes and rates of application. Application is by soil treatment. Two formerly widely used insecticides are no longer available: Diazinon and Dursban. The former is banned by the Environmental Protection Agency (EPA) for residential use. The latter is banned for endangering humans and wildlife. Imidacloprid is 90% effective against young grubs, but it has a high hazard rating for honey bees, harms other pollinators, and is a moderate hazard for humans and mammals. It is a systemic neonicotinoid, absorbed by the treated plant, making all or part of it toxic. It can impact other insects as well. The toxicity via skin exposure is very low, but it is moderately toxic if ingested. Trichlorfon is more than 75% effective. It is relatively nontoxic to honey bees, and is safest when applied in the evening or early morning. It has low toxicity for people and pets. Applied at egg-hatch, beginning around mid-July, the growth regulator Halofenpzide is about 75% effective. Unfortunately, killing the grubs under your lawn will not prevent adult beetles flying in from other lands to eat your plants. See also Hired Assassins above.
To wisely and appropriately treat a Japanese beetle problem (adults as well as grubs) — at any stage — you need to know their number and location. We’ve already noted the significance of the lingering of birds and some mammals on specific patches of lawn. Also, look for irregular brown spots on the turf. If a grub infestation is bad enough, you’ll be able to literally peal or roll back the lawn. This is because the turf’s root system will have been consumed. Grasses will no longer be securely anchored to the ground. If there is not an infestation and roots remain viable, you will be able to pat in place the portion pulled up; water it and no harm will have been done. Survey methods and guidelines are explained in Managing Japanese Beetles: A Homeowner’s Handbook.
PESTICIDE WARNING
Pesticides (which include herbicides, insecticides, rotenticides, etc.) are poisonous. Always read and carefully follow all precautions and safety recommendations given on the container label. Store all chemicals in the original labeled containers in a locked cabinet or shed, away from food or feeds, and out of the reach of children, unauthorized persons, pets, and livestock. Consult the pesticide label to determine active ingredients, signal words, and proper protective equipment.Pesticides applied in your home and landscape can move and contaminate creeks, lakes, and rivers. Confine chemicals to the property being treated and never allow them to get into drains or creeks. Avoid drift onto neighboring properties and untargeted areas.
Sources
Featured image: Adult Japanese beetle. Photo: Clemson University-USDA Cooperative Extension Slide Series, Bugwood.org, CC BY 3.0 US.
If you’d like to create your own personal or featured image of a Japanese beetle – not just a photograph or a memory – try drawing one. See How to Draw a Japanese Beetle.
“Biology and Management of the Japanese Beetle.” By Daniel A. Potter and David W. Held. Annual Review of Entomology, vol. 47 (2002): 175-205. The PubMed page hyperlink above gives links to freely available pertinent articles.
“Biology and Management of Japanese Beetle (Coleoptera: Scarabaeidae) in Corn and Soybean.” By Hailey N. Shanovich, Ashley N. Dean, Robert L. Koch, and Erin W. Hodgson. Journal of Integrated Pest Management, vol. 10, is. 1 (2019).
“Deadly Peril: Japanese Beetles and the Pestilential Immigrant, 1920s-1930s.” By Jennie N. Shinozuka. American Quarterly, vol. 65, no. 4 (December 2013): 831-852.
“Does Milky Spore Disease Work?” By Gary Couch. Cornell University Turfgrass Times (Fall 2000).
“Eleven Common Garden Pests: Identification and Management.” By Ralph Morini. The Garden Shed, vol. 8, no. 6 (June 2022). Piedmont Master Gardeners.
Home Grounds & Animals: 2023 Pest Management Guide. Publication 456-018 (ENTO-523P). Also known as 2023 Pest Management Guide — Home Grounds and Animals. May be purchased in a variety of forms. Virginia Cooperative Extension.
How to Draw a Japanese Beetle. Art for Kids Hub.
“Insecticide Residue in the Soil Harms Wild Bees.” By Ian Bennet. CAES Newswire, University of Georgia Cooperative Extension.
Insects and Diseases. Virginia Department of Forestry.
“Japanese Beetle,” by Daniel J. Clair and Vicki L. Kramer, pp. 89-107. In Eradication of Exotic Pests: Analysis with Case Studies. Edited by Donald L. Dahlsten, Richard Garcia, and Hilary Lorraine. Yale University Press, 1989.
“Japanese Beetle.” Horticulture and Home Pest News, Iowa State University Extension and Outreach.
Japanese Beetle. Animal and Plant Health Inspection Service (APHIS), U.S. Department of Agriculture.
Japanese Beetle. By Theresa A. Dellinger, Eric Day, Alejandro DelPozo, and Doug Pfeiffer. 2902-1101 (ENTO-514NP). Virginia Cooperative Extension.
Japanese Beetle Life Cycle (Video). By Bill Riden. Penn State Extension.
The Japanese Beetle Popillia japonica Newman (Scarabaeidea: Coleoptera). By Gale R. Ridge. The Connecticut Agricultural Experiment Station.
Japanese Beetle Program Manual. United States Department of Agriculture, 2022.
Japanese Beetles. By Daniel Frank. West Virginia University Extension.
Japanese Beetles. National Invasive Species Information Center, United States Department of Agriculture.
Japanese Beetles (Video). Dr. Donald Lewis. Iowa State University Extension and Outreach.
Managing the Japanese Beetle: A Homeowner’s Handbook. Animal and Plant Health Inspection Service (APHIS 81-25-003), United States Department of Agriculture.
“Managing Japanese Beetle and Variety Preferences in Apple.” Fruit and Vegetable News (November 23. 2020). University of Minnesota Extension.
Natural Products for Managing Landscape and Garden Pests in Florida. By Matthew A. Borden, Eileen A. Buss, Sydney G. Park Brown, and Adam G. Dale. University of Florida, Institute of Food and Agricultural Sciences, University of Florida Extension.
“A new threat to bees? Entomopathogenic nematodes used in biological pest control cause rapid mortality in Bombus terrestris.” By Alexandria Dutka, Alison McNulty, and Sally M. Williamson. Peer J, vol. 3 (2015).
“The Ornamental Garden in June.” By Susan Martin. The Garden Shed, vol. 4, no. 6 (June 2018). Piedmont Master Gardeners.
Popillia japonica (Japanese beetle). By M. Klein. CABI Digital Library, CABI Compendium. CABI (Centre for Agriculture and Bioscience International) is an international note-for-profit working in over 40 countries.
Put the Bite on Bugs. By Sue Smith-Heavenrich. Maine Organic Farmers and Gardeners Association.
Tachinid Flies and Other Natural Enemies of Japanese Beetles. By Paula Shrewsbury. University of Maryland Extension.
Tree and Forest Health Guide: A Handbook for the Diagnosis of Urban and Rural Forest Disturbances. Virginia Department of Forestry.
White Grub Management in Turfgrass. By Gary Forrester. Clemson University Cooperative Extension Service.
