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July 23, 2007
Gypsy Moth
I was away on vacation last week, and on our way to New York State, we drove across Pennsylvania on I-80. Although I have lived in Michigan for 26 years, I grew up in northern NY, at the edge of the Adirondacks. So, as we traveled across PA, the change from flatland Michigan (and Ohio) to scenic vistas with mountains and valleys was a welcome change. However, one aspect of the view was troubling -- quite a few spots had almost barren hillsides, caused by some defoliator. I guessed Gypsy Moth, and when we stopped at a rest area in central PA, I was amazed to see thousands of gypsy moths and egg masses on just a few trees.
We rarely have significant outbreaks of Gypsy Moth (Limantria dispar) in Michigan for a couple of reasons which I’ll describe later. Pennsylvania though, seems to have routine outbreaks, especially in the mountainous areas. Gypsy Moth females cannot really fly, so dispersal has to come in other ways. In the US, the two main methods are human-aided and wind-aided. Human-aided dispersal comes about when people travel from outbreak areas to other places, and unwittingly carry egg masses on items such as firewood, nursery stock, RVs, boat trailers, etc. It’s not so much of a biological problem as it is a social problem. If people are aware of this, then most of the time it is easy to spot the egg masses and remove them.
Wind-borne dispersal is a phenomenon more common to the hilly terrain of the eastern US, not flat Michigan. As the larvae hatch and make their way up the trees, they can be blown aloft and land on the next mountain ridge downwind. Therefore, populations can be more mobile than here in Michigan. That’s one of the reasons that these outbreaks can occur in places like Pennsylvania.
Michigan has also experienced a few outbreaks over the years, but they tend to stay localized and more recently, they have become quite the rarity. One of the reasons for the lower numbers in Michigan may be due to the fungus that attacks the larvae and kills them. Entomophaga maimaiga has become established in Michigan, and has severely depleted the populations in SE Michigan. So, the fungus and perhaps the lack of interesting topography here has aided in reducing the Gypsy Moth to local and occasional pest status.
Posted by mfobrien at July 23, 2007 03:57 PM