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Caterpillar Plague - Beaten, but not Broken

posted Jun 25, 2016, 8:05 PM by Greg Coffey   [ updated Jun 29, 2016, 8:52 PM ]
As southern New England recovers from a bout with Gypsy Moth caterpillars that is (according to many) the worst invasion since 1983, we're forced to ponder a few things:
  • Why are they here?
  • How does the invasion spread?
  • What slows down the wave of defoliation?
  • How do we deal with this in the future?

Why are they here?

Well, the nature of the beast is that some guy in the Boston, MA area released some accidentally in the late 1860s.  His start-up plan was noble; make a better 'silkworm.'  Unfortunately, this did not work, and the only thing this guy was able to start was a major forest pandemic for the subsequent years.

How does the invasion spread?

Like any other insect, gypsy moths and their caterpillars can move on their own.  No surprise there.  What many people might not think of is that they also look for vectors to increase their spread.  One such helper is the wind; caterpillars can spin fine threads and wait for the wind to take them to greener trees.  A byproduct of this spinning of strands is that the little guys hang from the skies (trees) like paratroopers, and can easily grab onto passing animals, people, and vehicles.  This also acts as a vector for their spread, and as we travel the roads of RI and CT, it is readily apparent that the busier the road, the more likely the trees are bare.

What slows down the wave of defoliation?

There are many natural factors that reduce populations, including predators and pathogens, but something we've noticed is that forested areas with a greater diversity of tree species tend to be better off than those areas that have a prevalent species.  Even oaks, when mixed in with many diverse hard and softwoods, are not as defoliated as a lone oak in a forest of maples, and far less damaged than an oak forest.  This may be because the more diverse forests harbor a broader range of predators, or even that the diverse wood will force the caterpillars into the open more often as they try to find suitable food.  Whatever the reason, biodiversity seems to be a good non-chemical means of slowing their advance.

How do we deal with this in the future?

We can safely bet that the gypsy moth isn't going away anytime soon, so we will need to address this insect as a part of our greater ecosystem.  Of course, nature will find a balance, so the various species that are least affected by the moth will do well in forests over the years until the moth has less and less food, and the populations balance out.  That said, we can also engineer our forests to include more diversity, and in so doing, establish trees that will replace those lost on account of gypsy moths.  Cultivating biodiversity is likely the option that will see the forests and the moths reach an equilibrium sooner.

We'll see...