I’ve seen these strange flower-like growths on Utah Junipers here in Southwestern Colorado for years, but have not known what they were. I assumed they were galls, but was having a heck of a time figuring out what type of gall they were. Finally, browsing Ronald Russo’s fine book Plant Galls of the Western United States, I found a good match.
These galls were probably caused by a Gall Midge – namely, Walshomyia sp A.
According to Dr. Russo’s book. there are at least four species of Walshomyia Juniper Gall Midges, which are, for now, handily called Walshomyia sp. A, Walshomyia sp. B, Walshomyia sp. C and (ready for it?) Walshomyia Sp D.
These are tentative species names, they’ll likely change as researchers do taxonomic work on the adult Midges.
There are approximately 6,650 species Gall Midges (midges in the family Cecidomyidiidae) described (‘known to Science’) world-wide.
However – DNA barcoding estimates that there are probably 16,000 species of Gall Midge…in Canada alone. This suggests that there are quite likely over one million species of Gall Midge world-wide.
If those estimates are reasonably accurate, then currently only 0.665% of the Cecidomyid species have been described by science.
And a substantial proportion of those species are probably ‘cryptic’ species – species that can’t reliably be identified by just morphology, even by experts.
I can’t help but think that DNA barcoding, similar to the somewhat controversial approach taken by Michael Sharkey etal, would be pretty useful in this situation.
These galls grow on the tips of the Juniper’s twigs. Sometimes they occur in clusters, touching each other.
The galls get more darkly colored and ‘open’ as they age. I’m not sure when the midge larva exits the gall, but the Russo book mentions that the larvae mature within the space of a single year.
I’ve noticed that trees with these galls seem to be patchily distributed. For example, when I’m out on a hike I may not see any galls for a while, but then come to an area where a lot of trees have galls. I’m not sure if that’s a real effect, or if I start looking harder for more galls after I’ve seen one.
I’ve not seen what I would consider a heavy infestation of these on any one tree. I don’t think that these galls do serious harm the trees.
It’s funny how having an identification for an organism, even a tentative or perhaps incorrect identification, makes me think about that organism more, and perhaps notice it more. Naming the animals, indeed.
Next year, I’ll keep an eye out for the other types of Juniper Midge galls.
An interesting aside – Juniper ‘berries’ are not really berries – they are highly modified cones. In most conifers, the scales of the cones dry and separate to produce the scaly ‘pine cone’ shape typically associated with the word ‘cone’.
In Junipers, however, the scales of the cone don’t dry out and separate – the what would be the scales remain soft and fleshy, and merge to form the covering surrounding the seeds, giving us the Juniper ‘berry’.
If you look at a Walshomyia sp A gall, it looks more like the typical ‘pine’ cone of a Conifer than do the Juniper’s actual cones (berries).
Walshomyia signals and subverts growth of the Juniper’s tissue, causing the Juniper to grow a pine-cone shaped gall, even though the Juniper doesn’t grow pine-cone shaped cones.
I wonder if there is a relationship between the factors regulating the growth of ‘pine-cone’ shaped actual cones in other conifers and Walshomyia‘s ‘pine-cone’ shaped Juniper galls.
Sources:
Russo, Ronald A. 2021. Plant Galls of the Western United States (Princeton Field Guides, 142). Princeton University Press. ISBN-10: 0691205760.
Wikipedia’s entry on the Cecidomyiidae – this is where I found the estimates of the number of Gall Midge species, as well as information on the number of currently undescribed speces.
Big Biology Podcast – Episode 110: Tempest in a barcode: how rapidly can we (and should we) identify new species? – A fascinating interview with Dr. Michael Sharkey, who has recently described over 400 new species of Braconid Wasps – based (solely?) on mitochondrial genetic barcoding.
