Japanese Beetles (from lower Michigan)

2014 August 13

I don’t see these Japanese Beetles (Popillia japonica) up around Houghton, but in the Lower Peninsula (and, I guess, in most of the eastern US) they are a common garden pest. These were in Sandy’s parents’ yard on August 1, 2013, busily engaged in trying to make more Japanese Beetles.

With the green pronotum, brown wings, and black-and-white-striped abdomen, I don’t think that they can be much of anything else. And, as an invasive pest species, the Japanese Beetle is also really common. So even if there is some native beetle species that looks similar, odds are that these aren’t it.

Given the tenacity of the mating pair, they don’t seem too concerned that I’m going to eat them. Or at least, the male thinks that continuing mating is more important than possible death. Given that they are not well camouflaged, and that they are almost completely unconcerned about me during mating, I have to assume that either their armor is so tough that nothing much wants to put in the effort to eat them, or they have some sort of chemical defense against being eaten.

The male’s legs don’t seem to wrap around the female, but he has a pretty good grip just hanging on to the edges of her shell.

And here’s another one that wasn’t actually mating at the time, for a somewhat better dorsal shot.

So, anyway, these evidently really are from Japan originally – they arrived in New Jersey around 1916, probably as grubs in the root-balls of imported trees. Their larvae are one of the varieties of white, C-shaped grubs that live in lawns and eat the roots of grass. In large numbers, they basically shear off the grass underground until it dies, and the dead grass can be peeled back to expose the grubs. They sometimes kill small trees and shrubs by eating their roots, too. Once they become adults, they eat the leaves of most common garden plants (particularly roses and their relatives), and also eat buds and fruit. And as imported pests, they don’t have many predators or diseases and so can build up to very large numbers.

There are a lot of products on the market to get rid of them, but you need to be cautious. For example, there are japanese beetle traps that do catch a lot of the beetles. Unfortunately, the traps lure in more beetles than they trap, and so if you put a trap near your roses, you’ll end up drawing in every beetle in the area while only trapping a fraction of them, and you are likely to be worse off than if you had no traps at all. So, if you do use traps, the best bet is to set them up fairly distant from the plants you are trying to protect.

There are several other control methods, but all of them evidently leave something to be desired. These include “milky spore” disease, parasitic wasps, certain insecticides, and simply not watering your lawn (if the lawn dries out, the beetle grubs mostly die off). I’m hoping that our long winters and cool summers will keep them from getting a toehold up here in Houghton, but we’ll have to see.

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