This Stinks!

Brown Marmorated Stink Bug (Halyomorpha halys)

Harvest is underway, and the nights are getting colder. All the little creatures, including stink bugs, are looking for someplace to spend the winter. A few have managed to get into the space between the windows and the screens, and one or two have made it all the way into the house. They’ll need to be vacuumed out.

The stink bugs we’re seeing are called brown marmorated stink bugs, And their name describes them pretty well. They are varying shades of brown on the top and bottom sides. Marmorated means marbled, so you can imagine the marbled veining or streaking like brown marble. Their overall appearance is like an oval or a shield, with their bodies being nearly as wide as they are long. They’re about two-thirds of an inch long as adults, with six legs and four wings.

The stink part of their name refers to the nasty-smelling chemicals they release when provoked or smashed. And the bug part refers to the fact that they are true bugs.

The term “true bugs” challenges my vocabulary, because for the most part, I want to call anything with six legs and two pairs of wings a bug. True bugs, however, are a particular kind of insect. Along with their shield-like shape, they have specialized mouth parts intended for sucking juices out of plants like a straw. Except their “straw” has two chambers—one for sucking up juices, and one for pumping chemicals into the plants to break down cell walls and start digesting the contents before the bug sucks it up. Very clever and efficient wouldn’t you say? And devastating to the plants. Aphids, cicadas, leafhoppers and bedbugs are some of the 80,000 varieties of true bugs.

These brown marmorated stink bugs hatch from eggs laid in clutches on the undersides of leaves. They go through five instars. That is, they grow and shed the hard covering that serves as skin and exoskeleton about five times, getting bigger each time. The nymphs have red eyes and look more and more like adults as they grow. As adults, they can live for six to eight months, and the female can lay over 400 eggs.

They can over-winter in a dormant state called diapause which is kind of like torpor. That’s why they’re invading the house—they need a cool, dry place to sleep until spring when they can start foraging and mating and laying eggs again. And because they like to huddle with their own kind, they very generously send out pheromones calling out to their kin “Hey guys, I found a great place for winter in this windowsill. Come join me and we can have a sleep-over! The more the merrier!”

With their specialized sucking apparatus, they like leaves, but they especially like plants with fruits from soybeans and corn to peaches and apples. Farmers hate them for obvious reasons. On the other side of the equation, bats, birds, assassin bugs, other types of stink bugs, spiders and parasitic flies like to eat them. This isn’t enough to keep their population under control, though.

These little bits of brown marble are not native to the Americas. Their homeland is in Asia. Like so many other plants and insects, they were accidentally introduced sometime in the 1990s. The first official sighting occurred in Pennsylvania in 2001. Over the past twenty-odd years, they’ve spread throughout the country, damaging crops as they migrated into nearly all fifty states.

Scientists went to Asia where the stink bugs come from, and looked for their natural predators. Maybe whatever controlled them there could work in the United States as well. That might lessen the need for chemical pesticides. They discovered the samurai wasp (Trissolcus japonicus) and brought it back to study in careful quarantine lest it escape and add to the growing list of harmful invasives.  Would this wasp pose any threats to native species?

That’s the question scientists were trying to answer by using captive wasps under controlled conditions. Until 2014, when this little black wasp with clear, yellow-veined wings and no stingers came along on its own in a shipping container or some other transport and is now on the loose. This little wasp deposits each of its eggs into the egg of a stink bug. The baby wasp matures inside the stink bug egg, killing its original inhabitant and emerging ready to mate. In its native Asia, the wasp parasitizes 90% of the stink bug eggs, keeping the population of stink bugs under control. Whether it will stick to its original host in its new home is the question. Iowa has at least seven other species of stink bugs, some of which are beneficial.

Meanwhile, clouds of those brown stink bugs came flying out of the soybean field the other day when the combine went through. They’re definitely here.

Photo by: Author