Thursday, October 18, 2012

The Cutest Caterpillar Gall

  This must be one of the cutest galls, wouldn't you agree?
 Poplar Petiole Gall Moth gall (Ectoedemia populella)
   Among the many plant galls, this pea-sized gall on a Quaking Aspen leaf stalk has, perhaps, the most pleasant proportions.  Additionally, this cute, globular gall is a caterpillar-induced gall, which intrigues me.  The galler is the larva of the Poplar Petiole Gall Moth (Ectoedemia populella). This might be a small gall, but it represents quite a sophisticated life-cycle... and, what a ride that caterpillar must have, living in a ball gall on the stalk of a Quaking Aspen leaf.
   Here is a photo of a gall-inducing caterpillar in its hollow, green home... 
 ... an edible home for the caterpillar produced by the aspen as a result of chemical signaling by the larva.  What an interesting expression of a plant-insect interaction.
  I suspect it is rather dark and claustrophobic inside that gall, as there is no exit hole until the larva leaves the gall to pupate on the ground. What about waste elimination?  Exchange of gases?  Temperature regulation?  Well, amazingly, the set up works.  The larva will someday turn into a minute moth and repeat the process next year.  
   I found some Poplar Petiole Galls when I expectantly walked up to some young aspen trees in the fencerow at a friend's farm (unfortunately the aspens in my backyard don't have any of these galls).  Sure enough, there on the first tree, at eye level, were a number of these caterpillar galls.
I was lucky, because the first tree I looked at had at least six galled leaves, but none of the other dozen aspen trees had any sign of these galls.
  In this close-up photo of the gall, I find it interesting how the gall has formed at the base of an otherwise normal-looking leaf.
The caterpillar that causes this gall is very small, but it is no small feat...
... to cause a gall to grow... where it can live as it feeds on the gall's interior... all without affecting the leaf.
gall of Poplar Petiole Gall Moth (Ectoedemia populella) on aspen
At least, by all appearances, the galling doesn't affect the leaf.  However, the galling may alter the leaf's chemistry... I read a study where the result showed the galled leaves have slowed decomposition rates.
  See: [A petiole-galling insect herbivore decelerates leaf lamina litter decomposition rates.  Functional Ecology, Vol. 26, issue 3, June 2012  pgs. 628-636.]  One of the authors recently showed me one of these galls and piqued my interest in searching for these galls.
gall on leaf stem of aspen
   Quaking Aspen gets its name from the peculiar way the leaves flutter so rapidly in the breeze.  With all that shaking and quivering, imagine the ride caterpillar has in its little gall.  I wonder if living in its tight quarters could be like a rocket ride in a space capsule, or perhaps a flight simulator.
   I did get a chance to introduce my boys and their friends to the little green worm within its "flight simulator".  Maybe the boys will grow up to be chemical ecologists, or astronaut.
   I wouldn't mind a few of these cute galls on my backyard aspens.

1 comment:

  1. another thing for me to keep an eye out for Dana.

    Lovely post.