You must admit that the Japanese beetle is a handsome insect. With iridescent coppery red wing covers and emerald green pronotum (the segment behind the head), it catches your eye. In fact, sometimes people mistake it for another little beauty, the dogbane beetle. The latter is a native one that feeds on dogbane and causes no trouble. The Japanese beetle is no problem in its native land, East Asia and Japan. But here, in North America, it is another story: it has been a headache for gardeners and farmers since its arrival in New Jersey around a century ago.
It most likely arrived in the root ball of some iris plants imported from Japan around 1911. It was first noticed a few years later, in 1916, in a nursery in New Jersey. In a couple of years, entomologists knew that they were facing a species new to the United States, and had tracked it down to its country of origin, Japan. It didn’t take long to realize the potential harm this beetle could do to crops and ornamentals and the war against the Japanese beetle began.
The control methods used in those pre-Rachel-Carson days read like a horror story. The earlier pesticides included arsenate of lead and sodium cyanide. Of course, these pesticides killed a lot more than the intended target. These methods did not prevent the spread of the beetle. Pest tracking maps show growing circles radiating from its place of arrival in New Jersey, like those caused by a pebble dropped in a pond. The hope of eradication was abandoned, and the goal became containment. Quarantines were enforced, but nothing seemed to stop the advance.
By the forties, a new pesticide, DDT, had emerged that was considered far more effective and less harmful than previous ones. At least that was the thought at the time. DDT did little to stop the advance of Japanese beetles. They were spreading farther and farther along the East Coast. But the Midwest and the West Coast were still safe.
Nowadays, there are gentler methods to control the Japanese beetle, biological controls such as parasitoids and pathogens. These are the ones that keep the beetle from becoming a pest in its native lands: parasitic wasps, called Typhia, nematodes and several bacteria. I am happy to report that a native wasp, the blue-winged wasp (Scolia dubia) has also become an enemy of Japanese beetles.
I am not trying to give advice on Japanese beetle control. There are several fact sheets easy to find in the Internet. But I find this detail delightful: Japanese beetle larvae like well mowed, watered and fertilized lawns. So, if you reduce the size of your lawn and keep it overgrown and somewhat thirsty and hungry, you are practicing Japanese beetle control. Tell that to your neighbors!
How did this non-native species become so widespread in a century? Looking at the Pest Tracker map, we see that it is present in all the Eastern US (purple) and absent in most of the West (green). Residents of Midwestern and Western states may breathe easier, maybe. It is very significant that here and there, all the way to California, there are yellow and brown spots that indicate that the beetle has been found or is being eradicated, respectively. So, the question is: how did the Japanese beetle manage to jump those huge expanses of beetle-free land? It is not a strong flier; it can travel as far as five miles, but usually doesn’t go that far. Left to its own devices, it would be reaching Ohio and North Carolina, at most.
The Japanese beetle has other means of transportation; that means us. We constantly move plants, produce or cut flowers cross country; the beetles hunker down on them or their root balls and go for the ride to explore new lands. A Kansas gardener describes a recent experience at a nursery in a blog, “Japanese beetles for sale? Really?“. To his dismay, he found rose bushes for sale infected with Japanese beetles. The owners knew about it, the authorities knew about it; but not much was done. Most of the state is or was fairly clean from this pest; but not for long, it seems.
We can draw a few conclusions from the saga of the Japanese beetle in North America:
1. Introduced plants create problems, not just by becoming invasive, but by carrying pests, which in turn become invasive. It seems that most insect pests are introduced and further spread via live plants.
2. The battle against introduced pests is not always a battle to preserve native plants. The war against the Japanese beetle has been aimed primarily to non-native farm crops and ornamentals.
3. In the long run, pesticides are not effective. Other, more natural methods work better.
Photos by Beatriz Moisset. Map by National Agricultural Pest Information System (NAPIS)
Beatriz Moisset lives in Southeastern Pennsylvania, studies pollinators and gives presentations at nature centers, garden clubs. Guide to Flower Visitors
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