Botany Photo of the Day
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January 18, 2017: Botany Photo of the Day is being actively worked on. Returning soon!

Artemisia tridentata and Rhopalomyia medusa

Artemisia tridentata and Rhopalomyia medusa

One of the responsibilities I have at the Garden is looking after the library. After trying (and failing) to identify this plant, I ordered a copy of Ron Russo's Field Guide to Plant Galls of California and Other Western States for the library as a reference. Though it didn't help in that identification, the book has quickly become a favourite among the staff here at UBC Botanical Garden for its crisp photography and intriguing subject matter -- I think there will even be a book review in our next issue of Davidsonia.

The midge-induced gall on this Artemisia tridentata (big sagebrush) is not accompanied by a photograph in the book. However, Rhopalomyia medusa is mentioned in the image-accompanied entry on Rhopalomyia medusirrasa, a closely-related species. On Rhopalomyia medusirrasa, from the book:

"This midge induces globular, leafy-pubescent, polythalamous [many-chambered] galls on the bud of Great Basin sagebrush (Artemisia tridentata). These large galls are actually composed of numerous leaflife structures that are covered with long, forked hairs...Galls begin development in October, rest during the winter, and reach full size the following spring. These spring galls measure 20 to 25 mm in diameter and contain up to four larvae. Adults emerge in April or May. The larvae, pupae, and adults of this species [Rhopalomyia medusirrasa] are basically indistinguishable from those of Rhopalomyia medusa. The major differences exist with the galls. The galls of the woolly bud gall midge [Rhopalomyia medusirrasa] have the long white hairs, while the galls of Rhopalomyia medusa are hairless."

Gall midges are relatives of pests known to many indoor gardeners, fungus gnats (search the UBC BG Forums for "+fungus +gnat" (without quotes) to see the many discussions). For photographs of members of the genus Rhopalomyia, head on over to Rhopalomyia. There are no images of either of Rhopalomyia medusa or Rhopalomyia medusirrasa, but you'll get a good sense of the various life stages of these small insect species from the others photographed.

I also note from this entry that I've never done an entry on Artemisia tridentata for BPotD. That's something I'll have to correct in the near future!


Thanks for the great post and terrific photograph.

Does anybody know the molecular mechanism of transformation of host tissue into gall tissue growth? (e.g. do the parasitic insects inject plasmid DNA?)

Chris, you may interested to try to locate Biology of Insect-Induced Galls, edited by J.D. Shorthouse and O. Rohfritsch, Oxford University Press, 1992 (found via Wayne Armstrong's excellent plant site, in this case, To Be Or Not To Be A Gall, specifically Initiation Of Insect Galls).

And to quote:

“According to K. Hori (Biology of Insect-Induced Galls, Chapter 10, 1992), salivary fluids of hemipterans (bugs) and homopterans (aphids) may include amino acids, auxins (IAA) and various plant digesting enzymes such as pectinases, cellulases and proteases. The precise mechanism by which these chemicals induce cell division and morphogenesis is very complicated and varies with different species and even with different types of plant tissue. An increased concentration of certain plant hormones in the gall tissue may also be important for the morphogenesis of some galls.”

Thank you Dr. Mosquin for the bonus edification of your response, and for the striking photo you posted today. The light and lens most beautifully revealed the delightfully unusual contrasts in color and texture between the foliage and the gall. Most appreciated!

I'm not a Dr., but you're welcome!

I am pretty sure we saw this in Death Valley last March and couldn't find anything about it. I'll see if Nhu or Jacob remember it.

The photo is really nice - almost looks like a partial desaturation!

My over-worked boss might kill me for offering such a service, but I work in the Botany-Horticulture Library at the Smithsonian Institution's National Museum of Natural History in Washington, DC, U.S.A. (Whew. That's a doozy.) and I want to invite you to contact us if you have any kind of reference question. No guarantee that we can answer the question, of course, but we sure will enjoy trying. At least, I will. Just don't tell her that I sent you...

Wonderful resource you have here, Daniel. I look forward to this email everyday. Keep up the good work!

at first glance, i thought this might be a follow-up of the 'galloping moss', and this being 'moss riding bareback on sage', but no, just a midge.

Beautiful, and really interesting.
I read somewhere that folks were researching the gall-forming mechanisms connected to cancer or something... Should I ask the Smithsonian?

Connie - Nothing I know of off the top of my head (I say with honest humility - I am very low on the Bot-Hort totem, as I am just getting started) but I will pass the word around and do my own reference research, and if I get a good response I will post it here as soon as possible.

I am learning that botanists are warm but complex bunch and after the day I spent helping a pair of old, seasoned researchers decide what kind of holly was planted on the Constitution Ave. side of the museum I know better than to mess with a botanist trying to identify a plant...

Beautiful photo. I find galls really interesting. I didn't realize they could look like this; I've only noticed the spherical or lumpy forms. Amazing.

One learns much when they come here. At my age I will probably remember little. But the photography is excellent and this in my layman's term is pretty. :-)

Carrie, that's an intriguing offer, and I'm sure I'll be taking you up on it from time to time.

our local paper has write up from ap legal writer about how the flowers
comeing into florida have to be checked for bugs and drugs,with valentine
season miami airport is very busy at this time of year the agents can find 90
pests a day that could be dangeous here in the usa

thank you all

The light and color in the photograph are outstanding, as is the intriguing structure built by midges. Nature is so cool.

The Medusa mythology is facinating. I found the following in Wikipedia
In a late version of the Medusa myth, related by the Roman poet Ovid (Metamorphoses 4.770), Medusa was originally a ravishingly beautiful maiden, "the jealous aspiration of many suitors," priestess in Athena's temple, but when she and the "Lord of the Sea" Poseidon lay together in Athena's temple, the enraged Athena transformed Medusa's beautiful hair to serpents and made her face so terrible to behold that the mere sight of it would turn onlookers to stone (in some accounts Poseidon raped/ravished her). In Ovid's telling, Perseus describes Medusa's punishment by Athena as just and well-deserved.

These myths were not for the fainthearted!

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