Parasitic gall wasps

Where it all began

Unknown insect gall

06 November 2013

During a photowalk at Huntley Meadows Park on 06 November 2013, I spotted an unusual growth on a branch of a Swamp Rose (Rosa palustris) plant. I spent several weeks during Fall 2013 carefully searching the same spot for Blue-faced Meadowhawk dragonflies (Sympetrum ambiguum) but never noticed the potato-like growth until after most of the leaves had fallen from the plant.

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.

Parasitic insect galls and gall wasps

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.

Parasitic insect galls and gall wasps

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.

IMG_6564

Photo used with permission from Charley Eiseman.

Charley shared another photo of a later-emerging, cleaner-looking gall wasp (~2.2 mm long).

IMG_6686

Photo used with permission from Charley Eiseman.

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!

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Photo used with permission from Charley Eiseman.

Where do we go from here?

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.

Related Resources:

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!

Copyright © 2015 Walter Sanford. All rights reserved.

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3 Responses to “Parasitic gall wasps”

  1. Mike Powell Says:

    This story took a long time to develop and I admire your persistence in pursuing it. It looks like. You did a great job in putting the info and photos together into a fascinating posting.

    • waltersanford Says:

      Thanks, Mike! I’m just naturally curious. The journey began with a couple of simple questions like “What is that?” and “What made that?” Turns out relatively little is known about the gall wasps I collected, other than the fact that they spend most of their life as larvae. Did you catch the reference to the parasitoids that feed on these parasites? Fascinating!

  2. Testing 1, 2, 3… | walter sanford's photoblog Says:

    […] insect gall on Swamp Rose (Rosa palustris). This gall was made by parasitic gall wasps (Diplolepis […]

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