Sunday, September 23, 2012

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

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.


Cindy said...

I went to the SOD map onine and there are no samples taken near Toro Park so that's interesting. If you see symptoms of SOD (particularly on bay leaves), you can call your County Agriculture Department and they might come out and take a sample. I've seen blue oaks and coast live oaks with nearly all their leaves stripped by oak worm moth caterpillar during a summer (especially when the winter was mild and did not freeze eggs and/or allowed generations to start earlier) but then looking fresh the next year. I don't recall seeing a lot of dead leaves, however.

Katie (Nature ID) said...

Oh, Cindy, you got me searching all over the place. It doesn't look like anyone has even monitored for SOD on this side of the Sierra de Salinas range, whereas Carmel Valley seems to be the northernmost point sampled in Monterey County. There are no CA bays at Toro Park, but I did see browned toyon. I'm also wondering if the short trees are actually interior live oak (yes, back to my perpetual what oak is it question), which is not listed as a host for SOD: Maybe the browning is due to an Armillaria oak root rot fungi?

Katie (Nature ID) said...

Erg, Cindy. I never heard back from our area's SOD guy. I'll try to query someone else.

John W. Wall said...

I just spent a few days at Asilomar and was amazed to see all the oak moths flying around, and all the trees with dead leaves. An occasional tree would be covered with dead leaves, except for a hand-sized patch at the tip of a single branch. Some trees were completely savaged, while the tree next door was completely untouched.

Katie (Nature ID) said...

Again, I'm trying to figure out where you're talking about, John. Asilomar has mainly Monterey pines and sand dunes. Some of the neighboring yards might have oaks, and I've seen what I think you're describing of one tree defoliated and the one right next to it not touched at all. I'm not sure dead leaves are due to oak moths. If it was in the late afternoon-evening, it could have been a termite swarm. I'm not kidding. I was chatting with a friend last week at Asilomar/Sunset and medium-sized flying insects were literally everywhere. He's extremely interested in oak moths and spearheaded the crusade against aerial spraying here, but he couldn't identify one on the wing in the dark. I caught one to show him why they were once called Isoptera. I'm curious and will check out Asilomar for myself, because we had 2 generations of oak moths at home (across town), but a 3rd never materialized.