Monday, December 10, 2012

What are these Moths doing out in December?!

Male moths hanging around a light at night.
Have you been driving around recently wondering what these drifts of bugs are flying in your headlights?  Shouldn't everything be asleep for the winter... well, not the aptly-named Winter Moth.  This is one of many introduced (non-native) predators that are attacking our local, native and landscaped trees.  While it is possible that these little winged beasts could defoliate and kill our trees, mostly they cause slightly less but still significant damage. So many people I talk to say, "do I really have to pay someone to take care of this?"  The answer is yes.

Winter Moth Fact Sheet (UMass)

Close-up of a male.  Identified by the vertical dark
banding at the bottom of the wings and the
frilly edges.
If you are in a town like Winchester MA, most of the trees were planted long before you were born, and many before your parents were born.  In today's world, we often have such a short-sighted view on that which surrounds us, but as we look at trees, we have to realize that their existence crosses generations and that we need to care for them for future generations to enjoy.

Often, prior to some simple education, I find people are reticent to spend much effort or money to care for their trees, but with a proper arborist and relatively minor annual expenditures, you can be rewarded with healthy and vigorous trees.  Some of these expenses, like pruning, are elective, but some challenges must be handled or the life of your trees can be threatened.

One such threat here in northern New England is the aforementioned Winter Moth (Operophetera brumata).  The moth looks, and is, benign, but the caterpillar in its earlier life stage is what causes such incredible damage.  This insect, introduced from Europe, has caused some real problems in Massachusetts in recent years.  Early in the Spring at about 50 Growing Degree Days(GDD), eggs hatch and small larval caterpillars seek shelter in swelling tree leaf buds.  They then grow by eating the tender, young leaves.  An infestation becomes evident when leaves emerge skeletonized or half eaten.

Most trees will send out a new set of leaves after the pests have rappelled on their silk to the ground, but this new leaf break takes tremendous energy reserves and over a few seasons of attack can wear down even the oldest and strongest of trees.  Young trees, especially fruit trees, can be defoliated and killed in just a few seasons.  The big targets for Winter Moth are Oak, Maple, Ash, Birch trees, but they love all plants in the Rosaceae family (Rose), which include many fruits like apple, crabapple, plum, cherry, Amelanchier and Hawthorn among others.

Physical barrier to keep females from climbing tree.
If you have lots of moths hanging around your outside lights or on your windows, you should contact an arborist and schedule spray treatments for next Spring.  The current applications for this pest are very targeted and not toxic, so you don't have to worry about non-specific chemicals being used and polluting your property.  Ask you arborist about this and they will gladly discuss the treatments.

There is also a physical, non-spraying option where a sticky band is wrapped around the tree and stuffed with a padding material to physically keep the females from getting from the ground up the tree.  It works, but in bad infestations these bands can get filled with moths which allows other moths to walk right over them.  The photo to the right shows a band from a local tree with just a few captured moths.

A female moth I found at night in a stand
 of trees by a local pond.
The life cycle of the Winter Moth is pretty cool.  In the late fall, usually after Thanksgiving, when we have a slight warming the male and female moths emerge from the soil.  The male moths have wings and they are the ones you see flying in front of your car and on your outdoor lights.  The females have minuscule wings and are not able to fly, so they come out of the ground and crawl up the trunks of trees where they are found by the flying males after they emit a powerful pheromone attractant.  The females then lay their eggs on the branches or trunk and die.

In early spring as the leaf buds start to swell, the larvae hatch and crawl into the leaf buds and eat their hearts out.  People have said that in bad infestations, you can hear the millions of caterpillars munching away.  If you are parked under an infested tree in early spring as leaves start to emerge, you car will be covered in little caterpillar poop that look like tiny poppy seeds.  Soon thereafter the inch long green caterpillars return to the ground and wait until the fall to emerge again.

Because this pest is introduced, there are no natural predators to control their unmanaged expansion, which is why we need to bring in people to manage them for us.  However, there is a parasitic fly native to Europe that controls populations there and has been introduced and been successful in Canada.  Currently people locally are breeding and introducing these flies here in an effort to control the moth.

If you live locally and have noticed these moths recently, please contact a well-regarded local arborist and have them assess your property for trees that host the Winter Moth.

A friend asked me the other day if they needed to worry about these moths getting into their house and eating holes in their nice natural fiber clothes, especially wool sweaters.  The answer is a simple no.  It is not a moth that eats your clothing but the newly hatched caterpillar.  This Winter Moth flying around is male, the females have no wings, and they do not eat in their short life cycle, and since, as males, they cannot lay eggs, you have no worries about any offspring eating your clothing.

1 comment:

  1. Oh boy another problem for our trees from invasive non native pests...I have not heard of them here and would not have thought we would have a this problem with our cold snowy winter, but that winter seems to be warming too...