CA oak moth ~ 10/21/12 ~ Elkhorn Slough

California oak moth
Phryganidia californica

For all the evidence I've seen of oak moths recently, like the total defoliation of oak trees at Garzas Creek and the crunchy munching at Toro Park, this is the first I've found the classic prolific pupae and moths on the wing this autumn.  Getting pics of the cloud of moths is difficult since they look like fuzzy tan blobs.  Even these photographs do a poor job at illustrating how the pupae were on any and every available surface.  We had oak moths like this at home this past spring, but for some reason a 3rd generation never materialized.  Country Mouse of Town Mouse and Country Mouse has a nice post of oak moths up near Santa Cruz.  This local abundance of oak moths leads into my next post...

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.

CA oak moth ~ 06/30/11 ~ Fort Ord

California oak moth on coast live oak
Phryganidia californica on Quercus agrifolia var. agrifolia
Fagaceae

The populations of the CA oak moth are known to fluctuate dramatically over the years in an apparent cycle. I tend to forget about them until I start seeing swarms of moths around oak trees on warm June or September/October afternoons. It's really quite an amazing sight. In places of heavy outbreaks, people who normally don't pay attention to such things definitely notice massive numbers of caterpillars swinging on lines of silk from defoliated oak trees and climbing everywhere to pupate, from tree trunks to buildings and cars. I've read the population cycle runs anywhere from 5 to 10 years. It seems to me this would be a difficult thing to monitor, particularly the relative numbers, length of time, and locations. What I recall is that one year it could be heavy out in Carmel Valley and three years later it could be heavy up in Aptos. I've even seen one oak completely defoliated and the oak right next to it not even touched. I wish I had taken notes and photos of my observations through the years.

Many people seem to get alarmed when their precious oak tree in their yard gets defoliated. They call out pest management companies to spray and inject pesticides. I think this is a waste of time and money. I also believe this is harmful to the tree, the fauna that depends on the tree, and surrounding wildlife, including birds that collect the acorns and other moths that don't even eat oaks. Some reputable companies will clearly state oak moth infestations generally only last 2 years at most and they will treat in the second year. Huh? Well, if you wait to the third year without doing anything, the moths mysteriously disappear anyways. Plus, the live oak usually recovers with vigorous new growth, which is not an annual thing for this evergreen oak. It's cost-free pruning with an added benefit of natural fertilizer from the frass. I've seen this first-hand in the oak trees next to our driveway; I actually think they look healthier now than a few years ago before defoliation from the oak moths.

I believe these regular population crashes are density dependent. My theory is that when you intervene in the natural cycle and artificially suppress the peak population size, you prolong the higher than average population numbers. Again just my theory, the reason for this is that parasitoids (tachinids and ichneumonids), viruses, fungi, other diseases, and predators that normally keep the oak moth population in check aren't allowed to do their job as effectively. You end up with a bedraggled oak (think how your hair looks without a hair cut for a long time) and the potential to prolong the stress of repeated partial defoliation, which could in the long-run do more harm to your oak tree.

Okay, I'll get off my soap box. For decent links with better information, check out Elkhorn Slough.org, University of California Hastings Reserve, Pests of Landscape Trees and Shrubs, and Tree Solutions (yes, a pest management company with well-written information).

ps 10/09/11 - The oak moths have started swirling around our oak tree en masse. Interesting to note, the tree itself does not look defoliated like I've seen other trees around town.