EcoPress

Newly Discovered Parasitic Species

By Theresa Barosh

Flower

Photograph of an open flower on Camassia next to a closed-bud gall (indicated by the blue arrow). Camassia galls are subtle and hard to see if one is not expressly looking for them.

My family and I strolled along a path in Oregon. We walked through an oak grove that had a thick ground cover of the wildflower Camassia in full bloom. I collected a few of these flowers, hoping to examine them under a microscope later. Suddenly, I spotted movement in the ovary of a specimen in my hand that I had just collected. I was immediately (and to my family, inexplicably) thrilled as this unexpected event unfolded.

I remember precisely how the ovary looked. It was a round, small sphere of bloated plant tissue, a little lop-sided, and mostly yellow-green with a hint of purple near the bottom. As something moved just below the surface of the ovary, I hoped that one of my many questions about this species would finally be answered, after almost three years of ecological research.

The research started when I joined Dr. Susan Kephart’s lab as a sophomore at Willamette University in Oregon. She investigates speciation with the study system Camassia (Asparagaceae), a beautiful Northwest wildflower. Earlier, her research team noticed that some Camassia buds were unusually large yet never opened their petals. Kephart wondered if some flowers were cleistogamous—self-fertilizing and forming fruits without pollinator visits. When she and her student Michael LaDouceur opened the “fruits” however, they found insect larvae inside instead of seeds.

I was offered the opportunity to lead the search to identify and study the tiny insect. By contacting entomologists and specialists, Kephart had learned that the larvae were likely specialized insects called gall-forming midges (small flies). Gall-forming insects alter plant form and physiology, often resulting in bloated plant tissue (the gall), within which larvae feed. These insects are diverse (e.g. beetles, wasps, and aphids) and form galls on a variety of host-plants and tissues (e.g. spruce needles, goldenrod stems, and oak leaves). Each galling insect species tends to be extremely specialized, requiring a particular host plant genus or species to be able to induce gall formation. Insect and plant biology must come together precisely to form an appropriate home for a given gall-forming insect species. Taking advantage of this, taxonomists often start the process of identifying the insect species by first identifying the host plant species. At the time, the plant Camassia had no gall-forming insects described in the literature: we were dealing with a new species of insect.

As an undergraduate student, I participated in naming and describing this new species of insect. I spent several years collecting, rearing, and documenting the newly discovered species; these efforts led to a co-authored publication in Zootaxa (Gagné et al. 2014). To identify the species, we reared adult midges to compare against known gall midge species. We needed adults because the larvae were too indistinct to differentiate between closely related species. This midge species requires a year to develop, and larvae must overwinter in the ground before emerging as adults, making rearing and identification of adults difficult to do in a lab. Post-doctoral scholar Dr. Kathryn Theiss and fellow students in our lab helped collect galls in the field and checked overwintering larvae in the lab. Many friends and family also supported, encouraged, and participated in my research efforts. My partner Sean Fogerty helped set up a time-lapse camera to monitor a galled Camassia population so we could observe gall formation in the field.

One of my most exciting moments in researching this new insect species occurred when my family flew from Colorado to Oregon for my graduation from Willamette University. They had not visited before, so I enthusiastically gave them a tour. When I showed them the oak grove and large population of Camassia wildflowers, I was excited to show them an abundance of galls in the understory. I collected a handful and used a pocketknife to open one of the small homes, exposing the larvae inside. They looked on, with a mixture of disgust and intrigue, as small larvae squirmed in the fresh air.

This was the moment that my family saw me suddenly become inexplicably thrilled. I had spotted movement in one of the intact galls in my hand. I do not remember exactly what I did in my excitement, but I do remember precisely how the gall looked. No petals covered the gall. I could see something moving just below the surface of the gall wall. I was hoping that a larva would make its way out of the ovary gall, a process that I had not yet seen despite years of observing the system.

My brother and I rushed the specimen to the lab so that I could place it under the scope and photograph the ensuing events. Slowly, we saw the tissue getting thinner; something was coming out. A small hole formed, and a large larva finally emerged (“large” being less than five millimeters long). At this point, I thought the spectacle was over, but soon after the first larva another yellow one popped out of the small hole, then another one, and another one still. My brother and I watched enthralled as nearly a dozen more larvae rapidly emerged from the gall, one right after the other. It looked like a conga line. Why did they all emerge at the same time? Did the leader have reduced fitness after expending so much energy to forge the first hole? Did the leader facilitate the emergence of its fellow larvae (which were probably siblings)? I now know how larvae emerge from the gall (to overwinter and pupate in the soil). Most importantly, this observation has led to many new research questions.

We were probably the first people to observe Dasineura camassiae larvae exiting a gall. It occurred in a unique manner, with all the larvae exiting quickly out of the same emergence hole this behavior has not been reported in other flower-galling midges to our knowledge. Gall midges often emerge through multiple exit holes.

Last year, we published the first description of this newfound species, Dasineura camassiae (Cecidomyiidae, Diptera; Gagné, Barosh, & Kephart, 2014). This research initiated my passion for gall-forming insect interactions with one another and their plant hosts. I now continue to investigate gall-forming insects and their community impacts in Dr. Paul Ode’s lab (CSU).

References:

  • Gagné RJ, TA Barosh, and SR Kephart. A new species of Dasineura Rondani (Diptera: Cecidomyiidae) in flower galls of Camassia (Asparagaceae: Agavoideae) in the Pacific Northwest, USA. Zootaxa 3900 (2): 271–278
  • Gagné RJ. 1989. The plant-feeding gall midges of North America. Ithaca (NY): Comstock Publications Associates.
  • Barosh TA. 2014. Camas Larvae Exiting Gall: https://www.youtube.com/watch?v=vowzfKa-O88
  • Barosh TA. 2014. Great Camas Growing: https://www.youtube.com/watch?v=uftsYtNxETs

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