Gall relationship speculation

I thought it might be fun to speculate together upon the possible relationships between a group of gall types I’ve been observing on Casuarina glauca. I’m keen to hear any thoughts or theories you might have about the possibilities.

I made this project journal post to explain the situation as best I could, with pictures:

I think my most plausible theory so far is that there’s something about the ‘fluffy ball galls’ that makes them an attractive spot for 2 or 3 other species to induce galls. The fluffy ball galls seem to be the common denominator.

This is kind of an update/ follow-up to my last post ‘the galls are making me crazy’. I’m still insanely curious about these particular galls, but between my little Inat project, making observations of the galls whenever I can, and learning a lot about Australian galls, I’m mostly avoiding madness. Really appreciate the encouragement I found here.

Anyway I’d appreciate hearing your thoughts about these galls and their connection to one another.


Cool galls! Your best bet to start solving these mysteries is to rear adult insects from the galls, and then collect and photograph them. They may need microscopic examination to confirm the species, but even with just some macro photos you can probably get to family or even genus. You might find some parasitoids of the gall-formers too. There is some advice on rearing by @ceiseman here. In your case, perhaps cutting a bit of stem with the gall and keeping it in a jar of water to maintain sap flow for as long as possible would be a good idea, inside a container sealed with a fine mesh.


Hey VC :smiley:

I couldn’t post a comment on your journal with the AU address, but I found your other closely related post and replied there, here it is:

Hope its of some help to you

Thank you @deboas. Yep I have to get myself set up for this.
I admit to having a bit of a weird hesitance about it because I’ll probably end up killing things. I’m not at all against it, I just want to be prepared to get as much information out of the process as possible so it’s a worthy sacrifice : )
I do have a decent macro lens which doesn’t get enough use as I find it a bit bulky for walking with.
I also intend to cut some galls open to see if I can learn anything from that. Again, I want to be prepared to get everything I can out of the process.
Thanks for the great advice and link, just the sort of info I need.


Thank you so much Ant! Such a thought-provoking response, it’s a huge help and exactly the sort of thing I was hoping for when I posted this. I’ll respond in some more detail when I’ve thought about it some more.

Happy it was helpful! I did a quick search for “galls Casuarina glauca” on Google Scholar, and it threw up a few relevant results.

This paper has some photos of galls that look not dissimilar to some of yours. As you get further into this, the authors might be good to get in touch with - they may well be delighted that someone else is also interested in Casuarina galls.

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Really interesting, and I wish I’d been aware of this sooner! I’ve just come back to NZ from Christmas break in Sydney.

So far Selitrichodes Utilis is actually the only Casuarina glauca gall i can ID to species level, thanks to that paper you linked to! Nearly all the observations of the species on Inat are mine.
I have speculated that perhaps the other C.glauca gall-formers are close relatives of Selitrichodes, but I have no way of knowing (yet). I definitely need to try and rear some adults. I just realised yesterday that I have access to a microscope camera thing, which should be a help.

Yep at some point in the future I’ll attempt some sort of contact with scientists, perhaps the authors of that paper or someone at the local University. Maybe it would be a good student project. It would certainly be worth a try. Or maybe someone out there is already studying these galls?

Finally dissected some galls yesterday, I’ll have the observations up soon. They were from fallen branches so maybe not that fresh but it was interesting to see the inner structure. I did find one larva but of course have no idea whether it was the gall former.

Thanks again.

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Thanks! It took a bit of courage to post here as I wondered if anyone else would find it interesting. If you’re ever in Sydney again please do keep an eye out for these galls, I would love some more contributions to my project, it’s mostly just me at the moment.

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Hopefully later this year :)