California wild rose (Rosa californica) at the Carpinteria salt marsh
When I’m poking around at the Carpinteria salt marsh the thing that interests me most is the marsh ecology. I’m fascinated by the densely layered relationships of all those plants and animals; preying on each other and being preyed upon in turn, competing and cooperating, part of in an incredibly complex network of co-evolved interactions.
Here are a few photos I took recently in the patch of California wild rose (Rosa californica) that borders Ash Avenue. The flower at the top is not perfect, but its imperfections make it more interesting to me. I wonder what caused that damage to its petals.
Next are a couple of photos of a fungus I’ve noticed frequently in the marsh roses. It produces a bright orange fruiting body along the midvein on the underside of a leaf, causing the leaf to fold back on itself. A few years ago I asked Andrea Adams-Morden, head of the marsh docents and my go-to person for inane botanical questions, if she knew anything about this fungus, but all I remember is that she said it was a non-native rust, and she was hoping to have the plants treated to combat it. It made me sad to hear that, because I think it’s beautiful.
The next pair of pictures show some spiny leaf galls produced by a wasp, Diplolepis polita. The wasp inserts its egg in the leaf, and the rose responds by growing this outlandish, swollen, tumor-like structure, inside of which the wasp larva grows, feeding on the plant tissue. Gall researchers would love to understand better how this process works, but much of it remains a mystery. How do gall inducers manipulate their host plants’ normal growth pattern? What mechanisms are involved?
I’ve always assumed that the spikes on these galls reflect the wasp’s having taken advantage of the rose’s existing thorn-producing genetic code, appropriating it to better defend the gall from outside attack. And defending the gall is important: Just as the gall represents a successful exploitation of the rose’s resources, the gall itself is a resource that other organisms have evolved to exploit. As with most galls, the D. polita gall is prone to being targeted by other species, either inquiline species that feed on the gall tissue, or predators or parasites of the wasp larva the gall contains. There are even hyperparasites, wasps that lay their eggs in the larvae of wasps that laid their eggs in the larvae of the original gall inducer.
It’s kind of mind-boggling.
The galls darken as they age, eventually turning brown and brittle. The next photo shows what I believe is a younger gall, its spikes softer, more flexible; toward the middle of that photo two still-younger galls are just starting to emerge from their respective leaves. And in the lower right of the picture, something I didn’t even notice until after I got home and looked at the photo on my computer: A small female wasp, her long ovipositor resting on the leaf surface.
I’ve cropped in tighter on the wasp in the last image. It’s not a very good photo; I took these shots with my iPhone, and its built-in lens can only take you so far. I didn’t get any detail of the wing venation, which would have been really helpful for identification purposes. I’ve posted the image to Bugguide.net, though, in hopes that a wasp specialist will be able to tell me something more. This could be a D. polita female, looking to lay her eggs in the leaf tissue to start more galls. Or it could be one of the other five species of inquilines and parasites known to associate with D. polita galls. Or it could be some completely unrelated wasp that just happened to be in the vicinity. I’ll probably never know.
Update: A helpful user on bugguide identified it as being a cynipid gall wasp, a category that includes D. polita. So given that it’s a female gall wasp hanging out on a leaf right next to a bunch of D. polita galls, I think the chances are at least decent that that’s what it is. Which is pretty cool.