Archive for the ‘Invertebrates’ Category

More Fun with Rhopalomyia

Sunday, November 20th, 2011

I continue to be fascinated by the life history of the coyote brush bud gall midge, Rhopalomyia californica. Lately I’ve been wondering about the midge’s pupation and emergence events. Russo writes in Field Guide to Plant Galls of California and Other Western States:

When fully grown, larvae burrow to the surface of the galls, where they develop their partially protruding white cocoons and pupate. This species represents one of the rare situations among gall insects where fresh galls and emergence of adults occur throughout the year, depending on location and environmental circumstances, even though there is a pulse of growth and gall activity in spring.

I’ve looked for, but so far have never found, a gall with intact pupae visible on its surface. I’ve found plenty of galls with spent exuviae, however. Here’s one I found a few weeks ago at the salt marsh:

Here’s another gall with visible exuviae. In this case, there are actually several individual galls that I assume were the result of the same egg-laying session, though they have not merged into a single gall, as they often do. I took this shot on the morning after our first good rain of the year; I think the exuviae on the left side of the large gall may have been knocked downward by raindrops:

Here’s a gall with an odd bumpy surface:

For those who don’t want to click through for the full-sized images, here’s a cropped portion of the previous shot so you can get a good look at the exuvia:

I don’t know how long pupation lasts, but I suspect it isn’t very long, or else I should have been able to find some galls with intact pupae protruding from their surfaces. Or maybe I’m misinterpreting Russo’s description of what the pupation stage looks like. Maybe the pupae are near the surface, or barely protruding, and the exuviae end up protruding as much as they do only as a result of the emergence itself.

Here’s a gall with some interesting discolored bumps. I wonder: Could those be pupation sites? If I had cut that gall open, would I have found individual larval chambers under each of those bumps?

Cell biologist Peter J. Bryant at UC Irvine has a neat page on Rhopalomyia californica on his Natural History of Orange County, California web site. Among the photos there are several showing newly emerged male and female midges, the females identifiable by their orange abdomens swollen with masses of eggs.

Although R. californica galls are found mostly in coyote brush, they also can occur in other plants. Dr. Bryant’s page shows a gall in a leaf of black sage and the midge that emerged from it; Bryant used DNA analysis to determine that it was R. californica. He also has photos of four different types of parasitoid wasp that emerged from R. californica galls.

Dr. Bryant was kind enough to correspond with me once before (concerning the bolas spider). I think I might try pestering him again to see if he would be willing to give me any pointers on rearing R. californica galls to adulthood. I don’t necessarily want to harm the insects. Could I simply keep a removed stem in water? Or would it require a living, growing plant to avoid disrupting the lifecycle of the gall’s inhabitants?

Even if I successfully raise gall midges to adulthood, it seems likely that I would be disrupting their chance to successfully breed. The adult midge only lives for a few hours; I would essentially be sacrificing its life merely to satisfy my curiosity. Am I okay with that?

As a young boy I loved Hugh Lofting’s Dr. Doolittle stories. While writing this post I suddenly remembered a passage I hadn’t read in 40 years. It turns out to have been from Doctor Doolittle’s Garden. Doolittle, after long effort, has managed to decipher the language of insects, and has become fascinated by the Ephemera — insects with very short-lived adult stages, such as mayflies (Ephemeroptera) and gall midges (Cecidomyiidae). Doolittle and his young assistant Stubbins (of whom I was always deeply envious) bring a delicate fly into the lab.

We worked on him for half an hour and our results were very meagre. He had things to say, we felt sure. But it was a language new to us. Clearly anyone who has to pack his whole life into one day must talk very fast. We soon got the impression that he was really pouring out hundreds of words a second. Only we weren’t catching them quick enough.

“Look here, Stubbins,” said the Doctor, “we are being entirely heartless. We can’t let this poor fellow spend more than half an hour talking to us. Why, half an hour out of his life is a forty-eighth part of the whole. That would be nearly eighteen months for us. What must he think of us? Imagine anyone talking to you for a year and a half without stopping! Let him go at once. We must do this on a different system. We will catch several singly and only keep them in the apparatus for five minutes at a time, If we are swift enough with our note-taking, we shall perhaps be able to gather a little from what each one says and piece it all together afterwards and make something of it.”

The more I study R. californica the more questions I have. But in answering those questions, I don’t want to harm the object of my curiosity. I’ll have to think about this more.

Snail Mail

Saturday, November 19th, 2011

I’ve written previously about the decollate snails (Rumina decollata) that live in the marsh. These non-native predatory snails are sometimes used as a biological control for the brown garden snail (Cornu aspersum). My daughter Julia took this photo of one climbing in blue-eyed grass (Sisyrinchium bellum) at the marsh a few years ago:

In early September I received an email from Shoichi Sano, a graduate student working with Prof. Akihiko Matsukuma of Kyushu University Museum. Shoichi had seen Julia’s photo on Flickr, and wanted to know if I might be able to send them a snail specimen. By examining the DNA of R. decollata from different parts of the world, they hope to learn more about how the snails are spreading.

After receiving the email I kept my eyes open at the marsh, but for a while all I could find were old, dried shells. Then in late September there was a light rain one night, and the next morning I found a group of a half-dozen decollate snails crawling near the path that parallels Ash Avenue. Here’s the one I collected:

I’ve always had something of a soft spot for snails; they seem like such peaceful, inoffensive creatures (at least if you’re not their prey, or if your garden isn’t being consumed by them). Deb Talan has a song about snails, “Angels Marching”, on her Sincerely album, and the lyrics have always resonated with me.

So I felt bad about killing this snail. But I’d told Shoichi I would, and after researching how to properly preserve and mail it, I dropped the snail into an airtight aluminum pill fob filled with alcohol, wrapped that in enough paper towels to absorb any leaks, and put the whole thing in a padded envelope.

I felt a little anxious waiting in line at the post office. Would my packing job be deemed adequate? I had to fill out a customs form, which required a detailed description of what I was sending. I wrote, “Preserved snail specimen (Rumina decollata)” and handed it in. The postal clerk didn’t even raise an eyebrow. Moments later my “snail mail” was stamped and on its way.

After a few weeks I received an email from Prof. Matsukuma:

Dear Dr. Callender,

I received an animal of Rumina decollata from the Carpinteria Salt Marsh, California preserved in ethanol. Thank you very much for your kind help to obtain the animal from California.

In Japan the invasive land snail R. decollata was found first at Kitakyushu City, Fukuoka Prefecture, northern Kyushu in 1988. At present the snail dispersed in various regions of western Japan, including northern Kyushu, Shikoku, Kinki and Kanto districts. I am afraid the snail will be a serious pest for vegetables in our country near future. I believe studies of origins and migration of the snail are important.

Once again, thank you very much for your kindness.

Best regards,

Akihiko Matsukuma
Kyushu University Museum

It was flattering, if inaccurate, for him to address me as Dr. Callender; I’m not a PhD, or any kind of scientist (unless you count political science, my major in college, as a “science”, which I don’t). But it was fun to feel included, and to participate, in a small way, in doing some “citizen science.”

The Case of the Twisted Stem

Sunday, October 16th, 2011

Yesterday Linda and I took a brief hike on the Jesusita Trail in Santa Barbara. The area we were walking through was burned in a 2009 wildfire, but it has mostly recovered now. Still, there are signs of the fire — blackened stumps and twigs — if you look for them. There is also a fair amount of coyote brush (Baccharis pilularis), so naturally that ended up being the focus of my attention.

I was surprised to see that there were no Rhopalomyia californica bud galls on any of the plants. I’m not sure why that is. Maybe it’s a legacy of the fire, with the gall midges taking a while to reestablish themselves. Or maybe this is typical of coyote brush stands higher up in the foothills. The Jesusita trailhead is more than three miles inland, while most of my experience with coyote brush has been at the salt marsh and the Carpinteria bluffs, right next to the ocean. Maybe R. californica is more of a coastal species?

At one point I was looking at a spindly clump of burned stems emerging from the center of an otherwise-green coyote brush, when I realized that the exposed stems had the characteristic thickening of the twisted stem gall midge, Rhopalomyia baccharis. I broke off a few of the galls and brought them home for closer examination. Here they are in my hand, to give you a sense of scale:

If you look closely at this shot, you can see the elliptical openings through which the adult midges emerge:

I think these twisted stem galls are fascinating, and I’m always looking for them, but whether it’s that they’re actually rarer, or just that they’re harder to spot in the foliage, I almost never find them. I come across dozens of terminal bud galls for every twisted stem gall I find.

Back in February I found a coyote brush at the Carpinteria salt marsh that had a lot of twisted stem galls; eight or nine at least. I was excited by the find, but I was also in something of a hurry, so I just snapped a few quick photos, intending to come back later and investigate in more detail. Here are some of the shots I got:

The next chance I had to visit the marsh was a few weeks later. I assumed I’d be able to find the plant quickly (the galls gave it a distinctive, gnarled appearance), but I ran out of time without finding it. By the time I could get back to the marsh for a more thorough search it was early April. Even looking more carefully, though, I couldn’t locate the plant. One was in the right spot, but it was much smaller than the plant I remembered, and had no visible galls, so I dismissed it quickly.

Where were the stem galls? I really had seen them; I had photos to prove it. But now they just weren’t there. I wandered back to the center of my search pattern, next to the small coyote brush, and stood there scowling.

And happened to take a closer look at the plant:


I suddenly remembered a conversation I’d had recently with Andrea, the head of the docent program, about some new workers hired by the city, with whom she’d had words about their over-zealous pruning of the native plants. The workers had seen the coyote brush with its noticeably gnarled stems, and had done what any self-respecting gardener would do: They’d pruned away the damaged branches.

Sigh. My quest for twisted stem galls continues.

Three Dried Galls

Friday, January 7th, 2011

I’ve been reading Ron Russo’s Field Guide to Plant Galls of California and Other Western States. I first heard about the book several years ago from Andrea Adams-Morden, the head of the docent program at the Carpinteria Salt Marsh. It didn’t really excite my curiosity at first; I’d been drawn to the marsh by my interest in birds, and didn’t know much about plants and insects. Over time, though, as my appreciation of the marsh ecosystem grew, galls began to seem more interesting, and eventually I went ahead and bought Russo’s book.

I’m glad I did. Field Guide to Plant Galls is a book that combines lots of detailed technical information with an infectious sense of wonder. And it turns out that galls really are quite interesting.

Russo writes:

Galls are tumorlike grows of plant tissue produced by the host plants in response to the chemical and/or mechanical stimuli of invading organisms (fungi, mites, insects), resulting in accelerated production of plant growth hormones…

Since the galls of many insects (especially wasps and many flies) are specific to their species in size, shape, and color, there is most likely some genetic programming relationship between the compounds provided by the adults or larvae and the manifestations of plant cellular tissue as influenced by the host’s own hormones. Something in the chemicals provided by gall organisms directs the expression of normal plant genes in the development and expansion of the host plant’s tissues. Scientists have been looking for a long time for this “blueprint” that seems to control gall characteristics. This has become the “Holy Grail” of gall research.

The complex relationships between gall inducers, host plants, and the communities of inquiline and parasitic species that associate with them are fascinating — and mysterious. Again and again in the book, Russo calls attention to the limits of current knowledge. Science increases the amount we know, but it also increases the amount we don’t know, in the sense that the larger an island becomes, the more extensive its shoreline. Russo’s enthusiasm for splashing around at the water’s edge is contagious.

One interesting aspect of galls is that they can persist for a long time. In this post I’m going to look at three old, dried galls that I discovered on my botanical crush, Baccharis pilularis, long after the original inhabitants were gone.

Gall #1: Rhopalomyia californica

One of the most common galls on coyote brush is the one created by the coyote brush bud gall midge, Rhopalomyia californica. I wrote previously about finding this old, dried-out R. californica gall:


I had read that R. californica was used successfully to curb an invasive weed in Australia (not coyote brush, but a related species, groundsel bush, Baccharis halimifolia). Recently I googled up some interesting material about that.

The host specificity of Rhopalomyia californica Felt (Diptera: Cecidomyiidae) and its importation into Australia as a biological control agent for Baccharis halimifolia L. is a journal article by W. A. Palmer, G. Diatloff, and J. Melksham. Originally appearing in Proceedings of the Entomological Society of Washington in 1993, it includes this description of R. californica’s life cycle:

Briefly, adults emerge from the gall in the first few hours after daybreak and mate soon after their emergence. Males are particularly short lived (2-4 hours) while females live 12-14 hours and occasionally longer. Females can be recognized by their orange abdomen, the coloration of which is caused by the mass of vermillion colored eggs. They oviposit approximately 100-150 eggs on the surface of meristematic tissue at stem terminals and occasionally in leaf axils. Neonate larvae enter the stem between bud scales and produce a gall on the stem. A number of larvae form a community gall and these galls can contain more than 50 chambers each housing one larva. The larvae complete their development and pupate within the gall. Flies emerge within two months after oviposition.

I also found a Google Books link for Pests of field crops and pastures: identification and control by Peter T. Bailey. The book includes this photo of a female R. californica laying its eggs on B. halimifolia:

I still haven’t seen an adult midge on coyote brush, but I’ll have a better idea what to look for now. I also really want to see a gall with the insects’ pupae protruding from its surface, or with the spent exuviae left behind after the adults emerge. Chuck Baughman has some beautiful pictures of what I think are exuviae (though he commented previously that he thought they might be the bodies of emerging adults killed in a cold snap); they’re definitely worth checking out at BugGuide: Coyote Brush Bud Gall Midge – Rhopalomyia californica.

Gall #2: Rhopalomyia baccharis

In many cases it is easier to identify gall-inducing insects by their galls, rather than by the insects themselves. That’s the case with another Rhopalomyia midge that forms galls on coyote brush, Rhopalomyia baccharis, the coyote brush stem gall midge. The insect itself is more or less indistinguishable from R. californica. But the gall it produces is very different.

I’d been looking for these galls (unsuccessfully) for the past few months, and then last week I noticed an odd thickening on a dead stem. It looked smaller to me than the galls I’d been looking for, but in hindsight that was my mistake; after removing the object, bringing it home and measuring it, I realized that it perfectly matches Russo’s description of “50 to 90 mm long by 5 to 8 mm in diameter”:

Once I examined it up close I was also able to see what I believe are the odd, elliptical openings that form at the outer ends of the gall’s individual larval chambers:

According to Russo:

The rounded-edged, elliptical holes are not typical of the normal sharp-edged, round exit holes created by insects, and they do not appear to have been chewed open. While we have no clear answer at this point, the convenient exit holes appear to be created by the plant after larvae have stopped feeding and stimulation from the larvae has ceased. These holes develop before the larvae (at the bottom of the chambers) change into pupae. Shortly after the holes are created, pupae develop and remain at the bottom of the chambers. Pupation occurs inside the galls, and the adults emerge through the openings in November and December. These unique circumstances make this species stand out from all of its relatives in which the pupae partially push their way out of the gall before the adult emerges. Much more needs to be learned about the habits of this mysterious and interesting gall midge.

Gall #3: Gnorimoschema baccharisella

My favorite line from the movie Men in Black is when Frank the pug observes:

You humans. When’re you gonna learn that size doesn’t matter? Just ’cause something’s important, doesn’t mean it’s not very, very small.

My final gall illustrates this point nicely.

I’ve written previously about the gall of the Baccharis stem gall moth, Gnorimoschema baccharisella. Here’s an image I previously posted of an old, dried G. baccharisella gall at the bluffs:

These galls are monothalamous, meaning that each gall contains a single larval chamber. Russo describes how the larvae chew exit holes, then drop to the ground to pupate. But that’s not the end of the story for the galls:

The frass that accumulates inside the gall serves as a culture medium for various fungi, which are eaten by several fungus insects after departure of the moth. Tilden (1951) found at least 10 parasites associated with this moth in addition to 17 other insects that were connected to the gall or the moth in some manner. The intricacies of these complex relationships stagger the mind for such a common, yet so disregarded, shrub.

The other day at the bluffs William and I came across an old G. baccharisella gall. I removed it and handed it to him, pointing out the emergence hole. He took his scientific curiosity a step farther than I had: He broke it in half.

Looking inside it, he made a discovery. “What are these yellow things? They look like eggs.”

They did. But after bringing the gall home and examining it more closely, I think they may be the fruiting bodies of some kind of fungus. Here are some closeups:

While examining these through the handheld microscope Linda gave me for Christmas, I noticed something crawling around. Here’s the video I took of it:

I’m not sure, but I think that’s a fungus mite of the order Mesostigmata (see, for example, this similar-looking mite at BugGuide).

I few years ago I would have overlooked all three of these galls. But with helpful people like Ron Russo showing me the way, I’m learning to look closer.

More Obsessing about Coyote Brush

Monday, November 8th, 2010

A running joke in my family these days is that I have a crush on coyote brush. We were playing “20 Questions” at the dinner table a few nights ago (anything to get William beyond grunting), and when it was my turn to choose and I announced, “vegetable,” William got it in one, asking with a roll of his eyes, “Is it coyote brush?”

Sigh. I can’t help it. That plant is just so cool.

I previously wrote about the infestation by what I believe was orange tortrix (Argyrotaenia franciscana) along the trail below the Sidenberg Overlook at the bluffs. The infestation was really bad for a while, but the plants have bounced back. Coyote brush has co-evolved with A. franciscana over a very long span of time; apparently the occasional infestation is no big deal. The same plants that basically had no healthy-looking foliage at all two months ago now look like this:

We’re reaching the end of the flowering season for coyote brush, and some of the female plants look like they’re covered in snow. Here’s a closeup of some seeds getting ready to set sail:

When you start paying attention to coyote brush, you can’t help but notice the great variety of insects that associate with it. Here are some photos I’ve taken lately.

Bob Carlson, a retired entomologist who previously did postdoctoral work studying Ichneumonidae, was nice enough to comment on these images I uploaded to Bugguide. He thinks the bluish tint to this small wasp’s eyes suggest that it might be a male (because it lacks the female’s long ovipositor) of the Agathidinae subfamily:

Here’s another wasp, this one crawling around on a Rhopalomyia californica bud gall. It’s not a great photo, but I’m wondering if this might be a species of Torymus, a group of parasitoid wasps that prey on the larvae of gall midges.

No luck so far on an ID for this fly, but after I posted its image at Bugguide and asked for any ideas about what was going on with that bubble of liquid coming from the fly’s mouth, I got a pointer to this interesting discussion: tiny bubbles.

According to my copy of Russo’s Field Guide to Plant Galls of California and Other Western States:

Coyote brush (B. pilularis), also called chaparral broom, is one of the most interesting shrubs entomologically. Tilden’s monumental study (1951) of this shrub identified over 221 species of insects associated with it, as well as eight species of mites. The insects, in turn, hosted an additional 62 species of parasites for a total of 291 species on coyote brush…

As mentioned earlier, the intricacies of host plants, gall inducers, parasites, and inquiline relationships, especially as exemplified by the coyote brush regime, are vastly complicated and a worthy subject for additional study in the future.

You hear that, scoffers? “A worthy subject”!

The Tilden referred to in that passage is James Wilson “Bill” Tilden, who passed away in 1988. He did his 1948 doctoral dissertation at Stanford on the insect associates of B. pilularis. The dissertation was 408 pages long, according to this obituary published in the Journal of the Lepidoptrists’ Society: James Wilson Tilden (1904-1988): A Remembrance (PDF file). I’d love to get a copy of that dissertation.

Not quite as long, but still very much a current object of my desire, is the “monumental study” Russo refers to, Tilden’s 1951 paper, “The Insect Associates of Baccharis pilularis De Candolle”. It was published in Microentomology, a journal that hasn’t yet made it onto the Web, unfortunately. The paper is 39 pages long, and according to a reference I was able to google up, they have a copy at the UCLA Biomedical Library. I think I’m going to have to pay a lunchtime visit to Westwood during one of the days when I’m working in Santa Monica.