Japanese Beetle Traps – Do They Work in the Garden?

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Robert Pavlis

Japanese beetles (Popillia japonica) have become a major pest in Eastern North America and other places. The Japanese beetle trap is routinely recommended for garden use and is easily available commercially, but does it work?

One of the problems with this trap is that it does “seem” to work – it catches lots of beetles. But does it bring all the neighborhood beetles to your yard? Will a Japanese beetle trap reduce the damage this pest does to your roses and other tasty plants?

The answer to these questions is a bit more complex than you might think.

Japanese Beetle Traps - Do They Work in the Garden?
Japanese Beetle Traps – Do They Work in the Garden?, photo source: Natural Insect Control

What is a Japanese Beetle Trap?

Commercial traps usually have a yellow top piece attached to some type of bag. A special chemical lure is placed near the top of the trap. Japanese beetles are attracted to the the yellow color but the chemical lure is the main reason they are come to the trap. Once they get to the trap, they fall in, and tend to stay there.

The lure can contains several chemicals. One is a female sex pheromone that attracts males. Another is a chemical that smells like one of their favorite foods, dead flowers, and this attract both males and females.

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If you have ever seen Japanese beetles on your plant, you can guess what happens in the collection bag – massive sex orgy! 🙂

Does the Japanese Beetle Trap Work?

Japanese beetles, photo source: Ryan Hodnett
Japanese beetles, photo source: Ryan Hodnett

I always get a chuckle when someone on social media claims “it works”, without ever defining the term. Without a definition, the claim is meaningless.

The trap certainly attracts and captures Japanese beetles but let’s face it, gardeners are not really interested in catching beetles.

They want the trap to protect their plants, so a more important question is, does it prevent damage to plants? If not – it is not working.

Does it reduce the population long term? Will the gardener have less pests next year?

How Powerful is the Trap?

Studies have shown that this trap can attract Japanese beetles from as far away as 5 miles (most claim half a mile). This is the reason some suggest that all the trap does is bring in beetles from the whole neighborhood, making the problem worse in your yard.

The reality is that climatic and wind conditions make it unlikely that a trap has such far reaching effects. Normally they attract beetles from a 250 ft radius. That means that in a normal urban setting, a single trap pulls in all the beetles from the homes you can see from your front and back door.

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How Effective Are the Traps?

Research has shown that Japanese beetle traps only trap about 75% of the beetles they attract. The remaining 25% end up near the trap feeding on plants.

The traps ability to protect plants in a garden depends very much on where it is located. When they are within 30 ft of the target plants, the traps do not reduce the damage to plants. In fact, studies show that damage may actually increase when traps are used.

The larvae density in turf is also not affected around traps which means the traps do not reduce the number of future beetles, at least no in your yard.

When traps are placed more than 100 ft away from target plants they can significantly reduce damage to those plants.

Most commercial products recommend placing them 10 ft away from target plants and that is far too close. I suspect they use this recommendation so that they seem suitable for even small back yards.

Spillover Issues are Important

Modified Japanese beetle traps with larger bags/containers, photo source: University of Missouri
Modified Japanese beetle traps with larger bags/containers, photo source: University of Missouri

When Japanese beetle traps are used in areas with a lot of beetles, spillover of the traps can become a major issue. This happens when the collection bags get too full and excess beetles are no longer trapped in the bag. In this case, the traps attract beetles to the area which then start feeding on plants.

This can be prevented by frequently emptying of the bags, or by using larger bags. Most commercial products are too small for a high load of beetles.

Some studies that have shown success with modified traps that have a very high capacity. In one case the bag was replaced by a 32 gal garbage can, or a four foot long mesh sack.

Low vs High Pest Pressure

In areas where Japanese beetles are well established and numbers are fairly high, the traps are less effective because the reduction in numbers is insignificant compared to the number in the area.

More success has been seen in areas with few beetles, in isolated populations or in areas where the beetle is just starting to establish itself. In such areas, traps can keep populations low enough so that they never get a foot hold, and never become a major pest. The traps do need to be deployed over the full area being controlled – not just one back yard.

Japanese beetle feeding frenzy, source: IPM University of Missouri
Japanese beetle feeding frenzy, source: IPM University of Missouri

DIY Japanese Beetle Traps

If there is a commercial product for a pest, there will also be DIY solutions.

A common suggestion to attract the pest is to use water, sugar, a mashed up banana and some yeast. This may attract Japanese beetles, but it will also attract all kinds of other insects, including beneficials, but it’s not particularly effect for Japanese beetles. If you are going to make your own traps, at least buy commercial chemical lures which are available as replacement items for traps.

DIY traps may be a good idea. Some traps are quite expensive, and as noted above, most have a bag that is too small. A DIY trap can work when combined with a commercial lure.

Should the Gardener Use Japanese Beetle Traps?

Traps are not very effective in a normal size yard.

They can be useful in two special situations. Traps can protect plants in larger gardens, if  the traps can be placed far enough away from the plants being protected.

Traps can also be useful where a whole neighborhood uses them. Beetles will not fly into your yard because the traps in other yards are keeping them there. A community using numerous traps can also catch enough beetles to impact the future local population. But this only works if everyone cooperates, and cleans the traps on a regular basis – something many people will not do.

Note: this post contains affiliate links to some products. I don’t endorse these products, but merely use the links as examples.

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Robert Pavlis

I have been gardening my whole life and have a science background. Besides writing and speaking about gardening, I own and operate a 6 acre private garden called Aspen Grove Gardens which now has over 3,000 perennials, grasses, shrubs and trees. Yes--I am a plantaholic!

27 thoughts on “Japanese Beetle Traps – Do They Work in the Garden?”

  1. I would love to see a post from you about milky spore…anecdotally it seems to have worked for me with Japanese beetles, but needs to be applied 3 x (Memorial Day; 4th of July; Labor Day) in my area (zone 4) for two years. After that I saw a substantial reduction in beetles. However I have no idea if it was a coincidence (the weather is different every year) and if I inadvertently harmed more beneficial species. Whatever the reason, the beetles were knocked back to a manageable amount, which I define as small enough to remove by hand. Curious to know the science here.

    Reply
  2. I had a major problem with japs in NY. I put a trap in all four corners of the yard. I was emptying 4 FULL bags a week the first year. The second year I barely filled one bag. The third year I was lucky to fill half a bag. I feel the traps do the job.I swear by them

    Reply
    • And what was the effect of weather?
      I have less Japanese beetles than 4 years ago – I did not use traps.

      You can swear all you want – the facts don’t change.

      Reply
      • Apparently Robert, one person’s eyewitness testimony does not constitute a “fact” in your eyes. But one thing you cannot dispute is this: a dead beetle does not reproduce.

        Reply
          • I would disagree. I’m sorry to say your article you linked to displays the kind of sloppy pseudo-scientific philosophizing characteristic of the likes of “skeptics” and “Scientists” (capital S) like Michael Shermer, Richard Dawkins, etc. Your definition of anecdotal evidence is so broad as to encompass pretty much everything:

            “Anecdotal evidence is an observation someone has made which has lead them to a conclusion or a belief.”

            Any scientific study is based on exactly this: someone made an observation which resulted in a conclusion. And guess what? That also is *eyewitness testimony*. All of scientific research is based upon human eyewitness testimony. And scientists, you may be surprised to learn, are humans

          • “Any scientific study is based on exactly this: someone made an observation which resulted in a conclusion” – perhaps you need to look into the scientific method?

            “All of scientific research is based upon human eyewitness testimony” – that is rarely true – it is almost always based on measurements.

          • Robert,

            When you say science is based on “measurements”, I think you’re missing the fact that it takes a human to make a measurement, and that human, when writing down the results, must give his/her eyewitness testimony as to what they saw when recording the results. So yes, all of science is completely dependent on eyewitness testimony.

            Keep in mind, I’m not really disputing your views as it regards the beetle traps per se; I’m disputing your dismissive attitude of anyone who might say they personally observed something that doesn’t agree with your alleged “facts”. When it comes to the real world, it’s rarely possible to introduce a true “control” into the experiment. So I for one will not so quickly dismiss someone’s observations if they say something has worked for them.

          • Most of the measurements in plant science are done automatically by machines. Nutrient values are printed out. Yield weights are read off from scales. Can a scientist lie about the results – sure. That is why other scientists reproduce the work. Very few results are “observational” in the hard sciences.

          • “Most of the measurements in plant science are done automatically by machines.”

            Machines are designed, maintained, and operated by humans. Simply using a machine to make an observation does not remove the fact that a human made the observation. Does wearing glasses over my eyes remove my human agency in looking at things? Obviously not.

            “Nutrient values are printed out. Yield weights are read off from scales.”

            … again, by humans.

            “Can a scientist lie about the results – sure. That is why other scientists reproduce the work.”

            Can those other scientists also lie? Yes, they can. Of course we wouldn’t expect that, but what if there’s a systemic bias for some reason about a particular thing?

            But you are right, reproducibility is the hallmark of good science.

            “Very few results are “observational” in the hard sciences.”

            On the contrary–if it’s not observational, it’s not hard science at all.

            https://creation.com/examining-historical-science

          • Writing down a number from a machine screen is a far cry from making and interpreting an “observation”.

  3. Hello… do you have any posts about ‘milky spore’ or ‘beneficial nematodes’? Wondering if I should spend my money on those! Thanks!

    Reply
    • no – not yet. nematodes do work provided you get the right kind for the problem you have and you apply them as per instructions.

      Reply
  4. This year is x10 vs last year. My neighbour has a trap. My method is soapy water flicking into the bucket. I killed around three hundred over a week last year, and they were gone. This year, it’s been fifty a day for two months. They just keep coming. Thanks neighbour. My grass is completely dead, his is a golf course….bet those grubs feast on the live side this time around. I can see five traps from my house looking in every direction, one is five feet away one the property line. All of the entire cities bugs are right here…

    Reply

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