The following photos were taken on 21 December 2015 at Huntley Meadows Park while field-testing a new Nissin i40 external flash unit with my Fujifilm X-T1 mirrorless digital camera and 55-200mm zoom lens (88-320mm, 35mm equivalent). The camera was set for “Forced Flash”: “Flash On, Fired” appears in the EXIF information for all shots.
The camera was set for Manual Mode: both Aperture and Shutter Speed were operator-selected; ISO was set to “Auto.” Notice the camera used ISO 800 for every shot. One obvious advantage of using a digital camera featuring a larger sensor — in this case, an APS-C sensor — is the camera can shoot relatively noise-free photos at higher ISOs.
Also notice the rich color in each photo, something for which the Fujifilm X-series of cameras is well-known.
Unknown blue-black berries. Alonso Abugattas, moderator of the “Capital Naturalist” Facebook group, speculates this is probably a species of greenbrier (Smilax sp.).
Turns out the growth is a gall caused by a parasitic wasp. Charley Eiseman, widely regarded as the go-to gall guy, said “It is likely a Diplolepis sp. gall.” Diplolepis is a genus of gall wasp in the Family Cynipidae.
Charley also said the only way to make a positive identification would be to collect a few galls in the hope of capturing some wasps when they emerged from the galls. In the interest of science, Kevin Munroe, manager at Huntley Meadows Park, kindly granted one-time permission for me to collect a few galls.
Waiting and watching
On 11 March 2014, three (3) insect galls — similar to one I photographed during Fall 2013 — were collected from Swamp Rose (Rosa palustris) plants located alongside the boardwalk in the hemi-marsh at Huntley Meadows Park. The largest gall was ~1.9 cm (~3/4 in) long. There was one small hole in the gall when it was collected; there were no holes in the other two galls.
The galls were stored indoors in a sealed Ziploc plastic bag for several weeks. I checked daily to see whether anything had emerged. At least once, moisture was wiped from inside the bag in order to prevent the galls from getting moldy.
04 April 2014
The following photograph is shown for scale: the insect galls (and later, tiny gall wasps) were stored in a Johnson Ziploc XL Sandwich bag; its dimensions are 7 in x 8 in (17.7 cm x 20.3 cm). I taped the plastic bag to the window of my apartment at the Beacon of Groveton in order to shoot still photos and video before sending the specimens to Charley Eiseman.
04 April 2014
Gall wasps began emerging from the galls on 03 April 2014. The preceding photos were shot on 04 April 2014, and the following movie was recorded on the same day. Individual specimens are ~2 mm (1/16 in) long.
Tech Tip: The preceding video looks better viewed in full-screen mode.
A closer look at what emerged from the galls
Charley Eiseman used a Canon EOS Rebel XSi, MP-E 65mm lens, and MT-24EX Twin Lite flash to shoot the following excellent macro photographs on 08 April 2014.
The first photo shows a gall wasp (~2.2 mm long) that was covered with “crumbs” from chewing its way out of the gall.
One parasitoid, shown below, emerged among tens of gall wasps: Eupelmus dryohizoxeni (female), 3 mm long. That’s right, this parasitoid feeds on the gall wasps that parasitize Swamp Rose — now there’s an interesting and unusual food chain!
The gall wasps collected at Huntley Meadows Park don’t seem to match any species in the scientific literature, so Charley Eiseman sent some specimens to an entomologist who specializes in micro-wasps. We are waiting patiently for the specialist to identify the species.
Editor’s Notes: Sincere thanks to Kevin Munroe for facilitating my amateur scientific investigation, and to Charley Eiseman for his extraordinary kindness in helping a virtual stranger!
The dictionary widget in Apple OS X defines “gall” as …
gall 3 |gôl|
noun
an abnormal growth formed on plants and trees, esp. oaks, in response to the presence of insect larvae, mites, or fungi.
• [ as modifier ] denoting insects or mites that produce such growths: gall flies.
The following photos show an unknown insect gall on Swamp Rose (Rosa palustris) spotted during a photowalk through the central wetland area at Huntley Meadows Park on 06 November 2013.
Closer view.
Wider view.
Charley Eiseman, widely regarded as the go-to gall guy, said “It is likely a Diplolepis sp. gall.” Diplolepis is a genus of gall wasp in the Family Cynipidae.
Thanks to Joshua Stuart Rose for providing a detailed answer to my questions, “What is the typical timeline for development of a gall like this one (including the life cycle of the insects living inside the gall), and what is the role of the “host” plant?”
Charley can correct me if I’m wrong, but the host plant is both protection and food for the gall inhabitant. The insect somehow incites growth of the gall, sometimes by bringing along a pathogenic fungus or virus, other times by releasing hormones or even segments of genetic material. The insect then eats what is growing in the gall’s interior. Meanwhile, the plant’s bark or skin, already adapted to protect the interior tissues of the plant, protects the insect right along with. The timeline is tough to figure without knowing the species, but if there’s anything overwintering in there, I would bet on its emerging from the gall in April or May. That’s assuming that it did not already emerge in the autumn to overwinter as an adult somewhere, or else emerged even further back in time so it could mate and overwinter as eggs, waiting to form their own galls after they hatch in the spring. Source Credit: Joshua Stuart Rose, member of the BugGuide group on Facebook.
Charley Eiseman added the following comment:
That all sounds right to me. I don’t see exit holes so I’m guessing there is still something inside. Also, it seems to be the case that stem swelling type galls overwinter. Source Credit: Charley Eiseman, member of the BugGuide group on Facebook.
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