Skeletonizing without a skeleton: The Japanese Beetle

by Brandon Herbst and Tori Dowd

The Japanese Beetle (Popillia japonica) is found in the Lehigh Valley but is not native to it, or the United States for that matter. As its common name suggests, it’s native to Japan and was first seen in the US during the early 1900s, most likely delivered here concealed in the soil of an imported plant. As of 2002, it has become comfortably established in at least 30 of the 50 states in the US. One reason possibly contributing to its wide coverage of the US is that there aren’t very many natural predators of the insect (Featured Creatures).

CC Some Rights Reserved Katja Schulz

The insect definitely stands out in its phylogenetic tree with its beautiful metallic green thorax, bold bronze wings, and white abdomen hairs. All that beauty isn’t made in a day, as it takes anywhere from 1-2 years to complete their development, depending on the climate.

Males tend to emerge earlier than females, but eventually, once the females appear, the sex ratio balances out to an even 1:1. Quickly after these beetles emerge, mating begins due to the strong sex pheromone released by the females. Once this pheromone is released, here come the males! Males swarm to the females in an attempt to mate. The insect participates in a competetive mating regimen where many males will crowd a virgin female after she releases powerful sex hormones, sometimes creating beetle “balls”. Due to this fierce competition, mating rarely occurs under this condition (Featured Creatures).

Because these beetles can withstand temperatures as low as -20 degrees celsius, US winters are no problem for the relatives of the scarabs of ancient Egypt. For those who are not interested in spraying toxic chemicals in their gardens, especially their vegetables, there are some eco-friendlier approaches. Japanese beetle traps do exist and they’re baited with both the beetle sex pheromone and floral scent to draw the beetles in. Since they are attracted to the scent, they fly to the trap, enter the bag and have no way of getting out. What’s interesting is the new idea of “mass trapping” the Japanese beetles. Mass trapping is used to lure in large quantities of pests in order to reduce the population. These mass traps are using the same two pheromones mentioned above that are used in the traditional traps. The major advantage of using mass trapping vs the traditional traps are that they catch a lot more in a shorter time, as well as they hold a lot more beetles so you don’t need to keep emptying the trap (Integrated Pest Management).

Another earth-friendly and very effective way to treat these insects is with a harmless bacterium called “milky spore” and a microscopic nematode. Paenibacillus popilliae, as it’s known to taxonomists, is target specific to the Japanese Beetle and prevents the beetle larvae from maturing upon ingesting it. It’s given its “milky” title because that is the appearance of the infected beetle after the bacterium’s spores have grown inside of it. (Biological Control)

Balls of Japanese beetles

CC Some Rights Reserved Shelby L. Bell

The Japanese Beetle’s main claim to fame is its flexible diet!  What makes it even more of a “double-threat” than many other insects is that both its larvae and adults munch the plants that we like! The larvae mostly focus on grass roots. The adults feed plant leaves – often eating the fleshy parts of the leaves – but leaving the veins – just like some kids refuse to eat the crust of their peanut butter sandwiches!   This feeding habit is called “skeletonizing”, since the leaves look like they are heading out for a Halloween party.

Japanese beetles skeletonizing a leaf

CC  Some Rights Reserved Daniel

Japanese beetles feed on over 300 different types of plants and costs the turf and ornamental industry an estimated $460 million in efforts to contain them (Managing the Japanese Beetle). Once they find a plant that they consider a good snack, they encourage damage to it by releasing a scent that other beetles can smell from a great distance away and are attracted to. The beetles swarm the plant because they are so attracted to the scent, which causes damage to the plant as a whole. Even though they don’t seem to be picky eaters, they do not seem to like plants such as boxwood, burning bush, magnolia or redwood, in fact cultivating these plants in your yard might be a natural way to keep Japanese Beetles away!

It is not the worst thing in the world to share our earth with these spectacular beetles, although their tiny velcro grasp can be frustrating. Their populations tend to fluctuate. If you have a beetle-rich year – don’t worry, they might not be back the next year (Japanese Beetle Populations). It is also good to know that there are some ways of keeping them at bay that doesn’t require the mutually assured destruction of chemical warfare, which don’t kill Japanese beetles but also other more charismatic members of their phylogenetic tree, like fireflies!  

4 thoughts on “Skeletonizing without a skeleton: The Japanese Beetle”

  1. Many times invasives do not have natural predators, so this comes to no surprise when I read it in the blog. What was surprising was how the beetle traps that were mentioned can be such an ecofriendly way to address these invasives- no more eating from my garden. It is also very interesting as to how scent comes into play in this blog from mating to initiating food frenzy swarming, oh my!

  2. I knew that Japanese beetles were invasive, I wasn’t entirely sure how they made their way to the U.S. until now. I had seen many of the traps over the years, they all had pretty healthy amounts of beetles inside. As for the parasite mentioned, I think it is an interesting way to help with population control, although I think convincing consumers to use this method might be a little hard to pitch?

  3. I remember when our Japanese beetle traps would catch HUNDREDS of these over the summer. In recent years, however, I have been seeing fewer and fewer of them, instead being replaced by the June beetles. We still have to deal with them attacking our roses but I’m definitely not complaining about that lack of them haha. Great blog post!!

  4. Wouldn’t it be cool to be these little beetles? It’s so cool that they’re able to withstand temperatures of up to -20 degrees Celsius!

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