Invasive species are everywhere: birds, bugs, fish, flowers, fungi. It seems that every time you turn around, a new invasive species has sprung up, each with its own inherent threat on the local ecosystem. What we don’t hear about, however, is often the solutions that are applied to address the problem.
Take for example the Japanese beetles in this photograph. What do you notice about them that is unusual? The white dots on their thoraxes. I pondered these, wondering if they were parasite eggs, warts or merely beauty marks. The number of dots differs on individual beetles, and some have none at all. Because of this variation, and the fact I had never seen them before, I was leaning towards parasites.
A quick trip to BugGuide.net proved me to be correct. They are indeed eggs, laid by an insect called the Winsome Fly (Istocheta aldrichi). This fly was brought over from Japan fairly recently to try to combat the Japanese beetle invasion. According to the information put out by APHIS (the USDA’s ANimal and Plant Health Inspection Service), this biological control is not currently available on a commercial scale.
Japanese beetles were (accidentally) introduced to the United States in 1916, showing up in a nursery in New Jersey. Since then they have moved throughout the eastern US, living now in every state east of the Mississippi except Florida and have now started to move across the river into the West.
Biological controls for Japanese beetles have been around for years, some longer than others. The one most of us are familiar with is milkyspore. This is a bacterium (Bacillus popillae) that attacks the beetle’s grubs. Bacillus thuringensis (B.t.) is another bacterium used to control the grubs.
Then there are nematodes. These are microscopic roundworms that actively seek out Japanese beetle grubs in the soil. They come laden with their own bacteria, with which they have a mutualistic relationship. When the nematode finds a grub, it inoculates it with the bacterium. The bacterium then multiplies, providing a food source for the nematode. Between the two of them, the grub has no chance and dies.
Then there are the parasites. Two parasites have been brought over from Japan, where they are natural predators on the beetles. One, Tiphia vernalis, is a wasp that parasitizes the grub. The female wasp digs in the soil to find a grub and lays her egg upon it. The egg hatches, the larvae feeds on the grub, ultimately killing it. The adult wasp mostly eats the honeydew produced by aphids that much on the leaves of maples, cherries, elms and peonies. They have also been seen to nectar on tulip poplar flowers.
The other is Istocheta aldrichi, the Winsome Fly. This fly is a solitary insect. The female lays her eggs primarily on the thorax of female Japanese beetles. When the maggot emerges, it bores into the body of the beetle, where it dines and kills its host. The cycle from egg to fat and happy maggot is short, so as a control measure, this fly is very effect. Female beetles can be killed off before they get a chance to reproduce. The adult flies feed on the nectar of another invasive: Japanese knotweed. Sadly, they have no adverse effect on this plant.
All around us these battles rage. Those of us who keep an eye on the natural world are fortunate when we encounter the action. It’s nice to know that Mother Nature can take care of her own…with a little help from us.
To read more about APHIS’s Japanese Beetle Control measures, visit: