I’m no entomologist. But, over the years of dealing with Japanese beetles, I developed a theory or two on these destructive insects. To be honest, my pest management tends toward the path of least resistance. And over the years of dealing with them, I discovered a strategy that is working.

According to an internet search, we learn Japanese beetles (Polillia japonica) are a species of scarab beetle, and adults have iridescent copper-colored elytra and a green thorax and heat. The beetles have been here more than a century, and were accidentally introduced to the United States on the roots of nursery stock from Japan brought in for the 1916 World’s Fair. Lacking any natural enemies which kept it in check in Japan, they quickly spread across the eastern and midwest states becoming a serious plant and agricultural pest.

As many of us are painfully aware, the beetles decimate roses. They eat the buds, the leaves, everything, and leave an ugly mess. They also attack a lot of other plants and trees, like the foliage of apple and other fruit trees and garden crops such as beans and raspberries. They eat all summer, lay eggs and then die.

Then their progeny, the grubs, develop in the ground where they feast on the roots of grass. As the weather gets cooler they burrow deeper into the ground to hibernate. Come spring, the grubs start for the surface and go back eating the grass roots. The use of Bacillus thuringiensis (Bt), a natural soil bacterium, is one suggested tactic to spread on lawns to kill the grubs. Its use must be timed properly to work.

Here’s where my “least resistance” kicks in, because I’d never remember when to use that stuff, and so I would be wasting my money and maybe even time and effort to use that method. Another common tactic are those plastic yellow bags that are hung to attract the beetles. I don’t use those either. Like the Bt, they are just something else you have to buy, and in the case of the bags — they usually make matters worse. The running joke is that you position those bags closest to your worst neighbor to attract the beetles to their yard.

All this leads to how my method of dealing with Japanese beetles makes even more sense — to me at least. It would appear on any given piece of property there can be a population of Japanese beetles that feeds and reproduces itself pretty much confined to that property where it has found a ready food source. In other words, those beetles are not migrating all over the place like pollinators do in search of food. Once they recognize a food source — like bad relatives — they move in to stay.

Let this beetle go. It has two spots of tahnid fly eggs on its shoulders and the eggs will hatch out and consume the beetle — killing this and many more beetles for you. Photo by Lynette Walther

So it stands to reason if you can reduce those free-loaders and keep their populations low, you’ve got the upper hand. In order to accomplish this feat, I have a natural ally in my war against those bugs. It is a tiny parasitic fly, a Tachnid fly that lays its eggs on the shoulders of the beetles. These days I rarely see any of the Japanese beetles because my method has proved so successful.

But back in time when those beetles were shredding my roses and raspberries, I started hand picking the beetles. Lots of people do this, and most of them just drop the beetles into a jar of soapy water. That works, but I take it one step farther.

Heres what I do: I grab a handful of the beetles. They don’t sting or bite. Then I carefully let one beetle at a time out of my grasp. This takes a bit of practice, but it does not take long to get the hang of it. I examine the shoulders of those beetles and if they have any little opaque white spots — I let them go.

The others that do not have the spots, get their shells cracked and dropped into a bucket. The beetles with the spots are free to go and eat, but at the same time eventually the “spots” will hatch out a batch of Tachnid fly larvae which will burrow into the beetle and consume it from the inside out. Grizzly for sure, but oddly satisfying. The more flies you hatch out, the more beetles will be destroyed. And after doing that for a summer or two I found that my population of Japanese beetles had just about disappeared and have yet to return. End of story.

Lynette L. Walther is the GardenComm Gold medal winner for writing and a five-time recipient of the GardenComm Silver Medal of Achievement, the National Garden Bureau’s Exemplary Journalism Award. She is a member of GardenComm and the National Garden Bureau. Her gardens are in Camden.