Rubber Rabbitbrush (Ericameria nauseosa) is one of the common native shrubs in the high desert of the Four Corners area. And it’s really common to see little fuzzy white balls attached to the Rabbitbrush stems. I was curious about these – so I looked them up in Dr. Russo’s Plant Galls of the Western United States. These fluffy white balls are galls of the Tephritid fly – Aciurina bigeloviae.
In the photo below, you can see a Rubber Rabbitbrush in the foreground. Those small white puffs are the Cotton-galls.
I decided to open one of these galls up to take a look inside.
The first one I opened up was empty. It looked like it had been occupied, though – there was a hollow ‘living space’ in the gall.
There were also some galls on dead twigs on the same bush. Those galls were more woody, and had shorter ‘wool’ on them. The galls looked older, less fresh, than the greenish galls.
I’m assuming that these were galls from previous years. I didn’t think that the galls had been the direct cause of the death of the twigs since I think I’ve seen older galls on living stems.
When I opened one of these older galls up, there was an empty fly pupa inside.
According to Plant Galls of the Western United States, adults typically emerge in the Springtime from the galls.
So…these being Winter and all, I should be able to find a ‘young’ gall that had either a live pupa or a Tephritid larva in it. I looked at another gall.
In this one, there was a small larva.
These observations were consistent with what the book said. The older gall, presumably from at least last year, had an empty pupa in it. It’s likely that either an Tephritid fly or a parasitoid emerged from the pupa.
The second ‘young’ gall I opened had a live larva in it. It would probably pupate this soon.
But what had happened to the larva that was in the first gall I’d opened? I couldn’t see a hole in the gall gall that a predator would have made. The only entrance I could see was where I’d snapped the gall off from its twid. Perhaps I’d inadvertently dropped the larva and not noticed? Hmm.
I’m fascinated by plant galls. The gall creator convinces the host plant to build a home. In this case, the fly or the fly larva suggested to the plant that it build the maggot a home, and the plant did.
It’s as if the parasite enters into a conversation with the host cells, infecting them with an idea that goes counter to the host’s interests. The maggot whispers to the plant: “Hey…Let’s build a hollow, thick-walled cell on your stem. I’ll live inside of it, and I’ll feed on you. And, oh! It would be nice if the shelter is thickly covered with woolly white hairs, okay?”.
And the plant does it. This strikes me as being very strange, almost like science fiction.
It also reminds me of the way that Hookworm larva (Trichinella) engineer their host cells, modifying a host cell to create a ‘nurse cell’ shelter and then encouraging the host to grow a supporting network of capillaries around that shelter.
So…is the Hookworm larva/nurse cell association a gall? Except it’s in animal tissue?
Sources:
Sources:
Russo, Ronald A. 2021. Plant Galls of the Western United States (Princeton Field Guides, 142). Princeton University Press. ISBN-10: 0691205760.
