Thursday, June 20, 2013

Gypsy Moth Caterpillars

Some of you may have noticed the large numbers of caterpillars in the oaks near #9 tee. These are the larvae of the Gypsy Moth (Lymantria dispar) and the have nearly defoliated some of the oak trees between # 6 tee and #9.
The brown looking trees in the middle of the frame have almost no leaves left.

I talked with the City of Ann Arbor's Urban Forest Planner, Kerry Gray, and looked at the trees. She noticed that a lot of the caterpillars had been infected with Nuclear Polyhedrosis Virus (NPV)  or Entomophaga Maimaiga (EM.) These two infections should keep the infestation of gypsy moths from getting out of control. 

NPV is a naturally occurring virus that spreads through colonies of Gypsy Moths. Infected caterpillars hang from the tree in an inverted v position. It is also the so-called "Zombie Virus." According to wikipedia,
 Zombie caterpillars is a fanciful description of the behavior of Lymantria dispar dispar infected with NPV. National Geographic described the gruesome effect of NPV; "The virus forces the "zombie" caterpillars to climb trees, where the invader eventually liquefies its hosts' bodies into a dripping goo."  Many news sources also reported the zombie-like effect of the caterpillar, stemming from the virus's ability to hijack the behavior and liquefy the caterpillar in order to spread the infection.

The fungus Entomophaga Maimaiga (EM) is an introduced pathogen of Gypsy Moths. That causes the caterpillars to turn rock hard and hang from the tree in a head-down posture.

Here you can see dead caterpillars hanging in both positions.

An oak with hundreds of dead caterpillars on the trunk.

This tree has a few more gypsy moths.

Kerry said that the trees will likely push out new leaves and should be okay. The only caveat would be if we have another extremely dry summer. In that case, we might have to water these trees in order to keep them as healthy as possible.

Looking up at the canopy of one of the oak along #9 tee.

This is all that is left of the leaves.


Brian Kuehn said...

I had noticed the defoliated trees at the beginning of #9 and wondered about whether there was a blight. I have seen similar patches of trees in Dexter. Good to hear that our little virus friends are taking care of the infestation.

Hilary Kimbel said...

Thanks so much for sharing this! Do you happen to know what kind of turf in Vancouver they use? I think I would like to get it for my own front yard...