CA oak moth ~ 09/23/12 ~ Toro Park

California oak moth caterpillar / California oakworm on coast live oak or interior live oak
Phryganidia californica on Quercus agrifolia var. agrifolia or Quercus wislizeni
Fagaceae

Coming down through Wildcat Canyon, I found great swaths of dead-looking oaks, yellowish brown and upon closer inspection severely munched upon by oak moth caterpillars.  I don't think the folks who named the canyon had this kind of wild cat in mind.

Sounds of drops like gentle rain and tinkly crunchy chomping surrounded me.  The smell in this area was distinctive, too, but I can't easily describe it.  The trail and nearby ground were completely coated in greenish tan pellets.  Frass.  Caterpillar poop. And lots of it! The most I've ever seen... which really doesn't mean much considering I don't follow the fluctuating annual cycles of oak moth populations all that closely.  I believe there are people who use frass mass to estimate population densities, so my assertion isn't totally out of the blue.  This past spring, I did casually notice oak moths were on the wing in full force unusually early on with a second generation flying in June or July.  Unfortunately, I didn't take notes of the timing and my recollection isn't specific, only that it was significant enough that I commented to a couple of Monterey City forestry fellows at the local farmers' market how I predicted this was going to be a booming oak moth year.  They laughed me off and politely disagreed.

The few green leaves I found here had become veritable buffet lines for caterpillars. What surprised me was finding so many feeding on dead leaves. Their mandibles have got to be industrial strength to masticate crispy dried evergreen oak leaves.  There were plenty of dead caterpillars that simply looked dessicated, but there were also numerous dead caterpillars hanging by their first prolegs, a sure sign of a viral and/or bacterial infection.  Interestingly, I did not find a single chrysalis (yes, I use this term for moth pupa in addition to butterfly pupa, if it's not covered in hairs or silk and hangs by a stalk).  I wonder if this 3rd seasonal generation will successfully pupate and emerge in the next few weeks, or if this is an early sign of a natural population crash.

Even when everything else is dried up, live oaks usually remain green all year round.  I doubt the caterpillars were directly responsible for the dried oaks, because I suspect their heavy feeding did not actually kill the trees.  Our unusually mild winter with very little rain was gentle on last year's overwintering early instar caterpillars and also water stressed the oaks.  However, there were numerous other oaks in the park that were still green and with significant numbers of oak moth caterpillars.  There is a part of me that wonders if this area, easily accessible to group picnickers, had been hit by Sudden Oak Death or an Armillaria oak root rot fungi.  I will be curious to find out if these oaks have a fresh flush of green leaves after the rains hit.

I blogged about CA oak moths once before, which is an unexpectedly popular post.  I've linked to the UC IPM Online site for CA oakworms in the scientific name ID above, and I don't recall why I didn't include it in my previous oak moth post since it's chock full of great information. Also, while doing another oak moth search, I found this fellow blogger Garden Wise Guy's post to be quite entertaining.

ps 09/26/12 - Thanks to Cindy at Dipper Ranch who commented and always gets me thinking about things.  I have such a difficult time IDing trees, let alone the confusing complex of oaks. I've edited the post above to include the possibility that the oaks I saw were interior live oaks and the possibility the browned leaves were due to an oak root rot fungi.  I'll see what I can do about contacting the proper agencies to check into this, because SOD is closely monitored.