It had been a while since I took my favorite walk at the bluffs, from the Lois Sidenberg Overlook down through the coastal sage scrub, and so I was surprised a few weeks ago when I noticed a big change: the coyote brush (Baccharis pilularis) is heavily infested with some sort of insect. The foliage of nearly every plant is filled with silk webbing, many of the leaves partially or completely eaten, and what looks like caterpillar poop (frass) sprinkled throughout.
At first I couldn’t see what was making the webs, but after a while, looking closer, I started to notice a few of these guys:
If I got too close or jiggled the foliage they would scuttle backwards, hiding themselves in the mass of leaves and webbing they had constructed.
I tried posting some photos to Bugguide, but haven’t had any responses so far. But I think I know what they are: orange tortrix (Argyrotaenia franciscana), a moth that is a common agricultural pest in the western states, especially near the coast.
Most of the coyote brush near the top of the trail is so infested that it’s hard to find a single clump of leaves that isn’t full of webbing. Other plants, which apparently were infested earlier on, have nothing but bare twigs at the outer tips of every branch.
I’m curious to see what happens to the coyote brush. There are a number of parasitic insects that prey on orange tortrix; my guess is that the outbreak will eventually be controlled by them, and the coyote brush will come back, just as it came back from being heavily pruned by green leaf beetle larvae, Trirhabda flavolimbata, at the marsh last year.
I think the coyote brush can probably handle the orange tortrix and leaf beetles, just like it handles the stem gall moths (Gnorimoschema baccharisella), bud gall midges (Rhopalomyia californica), and all the other creatures that live on it. They’ve evolved together, adapting to each other’s presence, and over the long haul the coyote brush seems to be doing just fine.