Japanese Beetles: 11 Facts You Should Know

About Japanese Beetles

Japanese beetles (Popillia japonica) are metallic green insects with copper wings, invasive in the US since 1916. Adults feed on over 300 plant species — roses, grapes, raspberries, and apple trees are common targets. Larvae (white grubs) damage grass roots underground simultaneously. A single established population can devastate a vineyard or orchard block within weeks.

This blog post has loads of interesting facts about  Japanese beetles you should care about.

They are Super Active at Night

Japanese beetles are most active at night and are not attracted to light — unlike most flying pest insects. Standard light-trap methods are therefore ineffective for this species. Nighttime scouting gives the most accurate population readings, and physical exclusion barriers must be fully sealed before sunset.

Japanese Beetles are most active at night. Light does not attract these bugs like many other types of insects. 

Their feeding habit is as follows

• Adult bugs feed on plant juices 
• Larvae feed on roots and tunnel through the soil. 

Sometimes they are referred to as”spotted cucumber beetles” because they eat cucumbers and squashes.

They are Easy to Spot

Adult Japanese beetles measure 8–11 mm and are unmistakably metallic green with copper-brown wing covers and two rows of white hair tufts along the abdomen. Their feeding pattern — consuming soft leaf tissue while leaving the vein skeleton intact — produces a distinctive lace-like damage pattern that allows identification even without seeing the beetle.

Japanese Beetles, unlike many pests, are easy to identify. 

Mature Japanese Beetles: 

• Measure about ½ long 
• Have silvery shells
• Have copper-colored wings 

Their harm is visible, as their pointed, biting mouthparts skeletonize leaves, leaving only the vascular region behind.

They Avoid Some Plants

Despite attacking over 300 plant species, Japanese beetles strongly avoid garlic, chives, catnip, tansy, and white geranium. These plants produce chemical compounds that disrupt the beetles’ olfactory signals. Interplanting these species near vulnerable crops is a documented low-cost suppression strategy used in organic pest management programmes.

They are known to consume around 300 different types of plants. They appear to dislike: 

• Boxwood, 
• Magnolia, 
• Redbud

Growing plant species that are not the preferences of the insect is one organic kind of Japanese Beetle Prevention you can use. However, it is not a failsafe strategy.

Short Life Span

Adult Japanese beetles live only 40–45 days above ground, but their underground grub stage lasts up to 10 months. The complete lifecycle takes exactly one year. This creates a concentrated damage window in June–August when physical exclusion with insect netting provides the most reliable crop protection..^[2]

The Japanese Beetle don’t survive long, with each beetle living about 1 Month and 15 days on average.

A short lifetime may appear to be advantageous for dealing with this native species. However, keep in mind that when there is an infection by a significant population, there will always be another one to take an individual’s position. 

That is why the Japanese beetle exists.

They Enjoy Sunlight

Japanese beetles are most active on warm, sunny days above 21°C, concentrated from 9 am to 3 pm. Overcast days below 18°C dramatically reduce feeding activity. Shade cloth over high-value crops creates a cooler, lower-light microclimate that naturally suppresses beetle activity during peak season — a dual-purpose benefit for temperature-sensitive crops.

On bright days, you’re most likely to witness a lot of Japanese Beetles. Their affinity for the sun is yet another reason you will easily spot them, since you’ll usually find them on top of your plants, lounging in the strong sunlight while they eat… your backyard space.

Group Feeding

A single Japanese beetle causes minor damage. But as it feeds, it releases congregation pheromones that attract dozens more. A group of 20–30 beetles can skeletonise a grape vine leaf in hours. This rapid aggregation is why infestations escalate fast — and why early detection and action matter.

Japanese beetles are often in big groups. One beetle isn’t likely to do much harm by itself.  But while it eats, it produces a Chemical substance known as  “congregation pheromone” to attract other beetles of its sort.

The particular Japanese Beetle will then appear to have invited all of his friends to feast on your plant with him. At this moment,  you will begin to observe the harm.

They Cannot Bite You

Japanese beetles cannot bite humans — their mandibles are adapted for leaf tissue and are too small to penetrate skin. Despite their alarming appearance when feeding in large clusters, they pose zero physical danger to people or livestock. All economic damage is restricted to plants.

Japanese beetles do not bite.  They might try to grip you using their mandibles. However, the mandibles are too feeble to harm you. 

The sharp spines on their legs may feel uncomfortable on your skin but that’s the farthest they can go. 

They are Repellent to Some Scents

Japanese beetles detect host plants and mates through highly sensitive olfactory receptors in their antennae. Natural compounds including wormwood oil, teaberry oil, and catnip extract disrupt these signals and reduce feeding. Neem oil-based products, which interfere with beetle chemoreception, are the most widely available commercial option for organic growers.

They use their antenna to detect odors that lure them to partners and different vegetation. Wormwood oil, teaberry oil, neem oil, peppermint oil, Wintergreen, chives, and garlic are fragrances Japanese beetles despise.

They Have No Natural Predators In Some Areas

In most of North America, Japanese beetles have no established natural predators — no native parasitic wasps, predatory beetles, or pathogens have adapted to control them at population scale. This predator absence makes physical exclusion netting with mesh ≤ 5 mm the most consistent long-term protection available for high-value fruit and ornamental crops.^[1]

Japanese beetles are a type of pest that is known to destroy crops. Unfortunately, they have no natural predators in the United States (which means you have to do it).

These beetles eat plants and leaves, which can cause plant death. As if this weren’t bad enough for farmers already, these beetles also spread diseases like coffee wilt and tomato spotted wilt virus! 

However, there are ways to control Japanese beetle populations by using insecticides or traps.

They Take a Full Year to Complete Their Lifecycle

The Japanese beetle lifecycle is precisely one year. Adults emerge in late June, feed for 6–8 weeks, lay 40–60 eggs, then die. Larvae hatch and feed on roots through summer and autumn, overwinter deep in soil, return to root zones in spring, then pupate into the next generation of adults.

This beetle spends around ten months as a larva under the ground. The white grubs return to the grass in springtime and start feeding on roots till late spring when they pupate. 

The pupae develop into adult beetles and emerge from the surface after about two weeks. It takes a year for this cycle to complete.

Removing Grubs in Your Lawn Will Not Prevent Adult Beetle Damage

Grub control reduces lawn damage in spring but does not protect your plants from adult beetles. Adult Japanese beetles can fly up to 5 miles — they arrive from neighbouring properties regardless of your local grub population. Protecting plants requires excluding adult beetles directly, not just targeting their larvae.

Avoiding grubs in your yard is an excellent lawn care strategy for preventing grass damage in spring and early summer-fall. On the other hand, Beetles are excellent fliers and can travel hundreds of miles to forage and mate.

Beetles frequently lay eggs in landscaping beds and fields. It is especially true when the ground is dry and firm. The grubs will then develop into beetles, which will consume the plants.

However,  you can control them manually. You can throw them off plants and drown and perish in a container of water and detergent. 

Collect regularly during the day, immediately after the sun shines and has heated the soil. Or you can collect them just before dark when females are preparing to lay eggs.

Manually selecting beetles from trees may appear to be a boring and challenging process – but you may be amazed at how simple and more effective it is in controlling them

How Do You Stop Japanese Beetles?

The most reliable long-term protection is physical exclusion using fine-mesh insect netting over plants during peak beetle season (late June – August). For immediate control, hand-pick beetles in early morning when they’re sluggish. Neem oil disrupts feeding but requires weekly reapplication. Never use pheromone traps near the plants you want to protect — they attract far more beetles than they catch.

• Exclusion netting — The most effective method. Fine-mesh insect-proof netting physically prevents beetles from reaching plants — 100% exclusion with no chemicals. Install before late June; remove after beetle season ends in late August. For grapevines and orchards, 32-mesh insect netting blocks Japanese beetles while maintaining airflow.
• Hand-picking — Most effective in early morning when beetles are sluggish. Drop into soapy water. Practical for small gardens; not scalable for commercial orchards.
• Neem oil — Acts as a feeding deterrent. Reapply every 7 days and after rain. Best as a preventive, not a curative treatment.
• Milky spore (Bacillus popilliae) — A biological soil treatment targeting grub-stage beetles. Takes 1–3 years to establish but persists for 20+ years once active.
• Avoid pheromone traps near your crops — Commercial beetle traps attract far more beetles to the area than they trap. Increase infestation pressure significantly.

Questions to Ask Before Buying Insect Barrier Netting

Before ordering insect barrier netting for Japanese beetle control, these 4 questions will reveal whether you are buying a tested product or a generic mesh:

1. What mesh aperture size does your insect netting use, and is it rated to exclude Japanese beetles? Japanese beetles are 8–11mm long. Effective barrier netting uses a mesh aperture below 5mm to prevent both adults and larvae. Suppliers who cannot specify the exact aperture are selling untested material.
2. What UV stabiliser loading (%) is in your HDPE resin? Quality insect netting uses 2–3% UV stabiliser. Budget products use 0.5–1%, which will become brittle and tear within 2–3 seasons under summer UV exposure.
3. Can the netting be re-used across multiple growing seasons? A properly UV-stabilised HDPE insect net should last 5–8 seasons. Ask for material data sheets or test results. If the supplier cannot provide them, the product likely does not meet professional standards.
4. Do you supply installation clips and fasteners sized for standard row covers and tunnels? Factory-direct manufacturers typically supply a complete system. Resellers often source netting and accessories separately, leading to incompatible fittings and edge gaps that allow beetles to enter.

References

1. USDA APHIS. Japanese Beetle (Popillia japonica). Invasive Species. Available at: aphis.usda.gov — Japanese Beetle
2. DiGiacomo, G., Nelson, S.G.A., Jacobson, J., Klodd, A., & Hutchison, W.D. (2023). Hail netting: an economically competitive IPM alternative to insecticides for Midwest apple production. Frontiers in Insect Science, 3. DOI: 10.3389/finsc.2023.1266426

Conclusion

We do not advocate using the Japanese beetle traps that are commonly sold in large box retailers. These can catch some insects but frequently wind up attracting millions of beetles to your yard to feed on your garden or grass.

Fertilizers are generally discouraged because they tend to kill other synergistic insects such as butterflies, honey bees, and earthworms. That’s why we encourage you to use natural methods such as insect netting to keep at bay.

EyouAgro offers the best and most effective preventive netting products for flower pests. We also provide advice on how to control Japanese beetles. Our products such as Japanese beetle netting is reasonably priced and come with a warranty backed and after-sale service. We provide a variety of related netting and accessories to meet your needs. Our primary goal is to make farmers’ lives easier and assist them in taking care of their plants. Our services are simply the greatest, and you cannot afford to overlook them.

Kindly contact us at info@eyouagro.com or visit https://eyouagro.com for more information.

Next Reading

Wildlife Friendly Netting: all you need to know

However, there has been a clamor for nettings that aren’t dangerous for the animals. Every year, countless animals are injured and killed by indiscriminate use of netting. Below is a guide on wildlife-friendly netting.

What Are the Differences Between 3-Bar, 6-Bar, and 9-Bar Netting?

3-bar netting has the widest gaps and is ideal for crops needing high airflow and less shading. 6-bar netting offers a balanced combination of airflow and shading, making it suitable for crops requiring moderate protection. 9-bar netting, with minor gaps, provides maximum protection from pests and sunlight but limits airflow, making it best for areas prioritizing shading and compact protection netting.

Peach Tree – 8 Most Common Diseases and How to Treat Them

There are many different types of peach tree diseases and each has its unique symptoms. In this blog post, we will go over some common diseases that affect peach trees and how best to treat them.