Photo details: Canon MP-E 65mm macro lens on a Canon EOS 50D, ISO 100, 1/200 sec, f/16, MT-24EX flash 1/8 power through diffuser caps
While photographing Acmaeodera tubulus and A. ornata a couple of weekends ago (see Springtime Acmaeodera), I came across this leaf beetle (family Chrysomelidae) of the genus Microrhopala¹. When I took Systematic Entomology (so many moons ago), beetles in this and related genera were placed in the subfamily Hispinae. That taxon has since been subsumed by a more broadly defined Cassidinae (Staines 2002), which also includes the delightfully odd tortoise beetles. There are several species of Microrhopala in North America – this individual can be diagnosed as M. vittata by means of its dull reddish elytral stripes, eight-segmented antennae, and smooth (not serrate or toothed) elytral margins (Clark 1983).
¹ Derived from the Greek micr (small) and rhopal (a club) – presumably a reference to its small-clubbed antennae.
Many leaf beetles are expert botanists, restricted to and able to discriminate a single plant species or group of closely related species for hosts. Microrhopala vittata is no exception, specializing on true goldenrods (Solidago spp.) and flat-topped goldenrod (Euthamia graminifolia) (family Asteraceae). Adults feed on leaves in the upper part of the plant, leaving numerous small holes, but it is the larvae that have the biggest impact on their host by mining within the leaves between the upper and lower surfaces. Larval mining eventually causes the leaves to turn brown and shrivel up.
This species has been widely studied by ecologists interested in understanding the impacts of herbivorous insects on their host plants and associated changes to plant communities that result from their feeding. While population densities of M. vittata are normally low, they occasionally reach densities that result in severe damage to their host plants. Such effects are not limited to the host plants themselves – Carson and Root (2000) found that outbreaks of this species on stands of tall goldenrod (Solidago altissima) in an old field dramatically reduced the biomass, density, height, survivorship, and reproduction of tall goldenrod, resulting in higher abundance, species richness, and flowering shoot production among other plant species as a result of increased light penetration. Conversely, in experimental plots where the beetles were removed, tall goldenrod developed dense stands that inhibited the growth of many other plants. These effects lasted for several years after the outbreak. Thus, the beetle can act as a keystone species² in old field communities, indirectly promoting woody plant invasion and speeding the transition of the old field to a tree-dominated community.
² A keystone species is one whose impacts on its community or ecosystem are large and greater than would be expected from its relative abundance or total biomass (Paine 1969). Popular examples include the beaver, which transforms stream communities to ponds or swamps, and elephants, which prevent grasslands from converting to woodlands through destructive tree removal. In contrast, trees, giant kelp, prairie grasses, and reef-building corals all have impacts that are large but not disproportionate to their also large total biomass and, thus, are not considered keystone species.
REFERENCES:
Carson, W. P. and R. B. Root. 2000. Herbivory and plant species coexistence: Community regulation by an outbreaking phytophagous insect. Ecological Monographs 70(1):73-99.
Clark, S. M. 1983. A revision of the genus Microrhopala (Coleoptera: Chrysomelidae) in America north of Mexico. The Great Basin Naturalist 43(4):597-617.
Paine, R. T. 1969. A note on trophic complexity and community stability. The American Naturalist 103(929):91–93.
Staines, C. L. 2002. The New World tribes and genera of hispines (Coleoptera: Chrysomelidae: Cassidinae). Proceedings of the Entomological Society of Washington 104(3): 721-784.
Copyright © Ted C. MacRae 2009
Beetles In The Bush 
Good post. Species that exploit a single or narrowly defined host species always fascinate me. I know there are all kinds of reasons why this is, but it seems so counter intuitive from an evolutionary perspective. Although, I’m no insect expert.
Thanks, cedrorum. Host specificity is an overwhelming theme among the leaf beetles, and they are an extraordinarily diverse family of beetles – perhaps a result of that tendency to specialize. It does provide a fascinating subject for ecological and evolutionary studies.
Life in a patch of Goldenrod is great. Your doing well with your new camera, grasshopper!
Now go find some Trirhabda.
Thanks, Kirk. I’m pleased with how my initial efforts have turned out. I need to develop better technique for holding the camera still though – sometimes I take the shot just kinda hoping that I had it framed and focused properly. Of course, having digital also allows you to just rip a whole bunch of shots until you’re sure at least one of them ‘hit’.
You might want to try a monopod, at least that reduces movement on one plane. I use a tripod as much as I can.
Hmm… one more thing to carry. I’m already usually carrying a net and beating sheet. Are there small, telescopic monopods that would fit easily into my camera backpack? That might be a solution. Or perhaps I could just use a handy stick – not ideal, but perhaps better than nothing.
Yes they do, check B&H Photo in NY.
Geez – I had no idea how many monopods there would be to choose from. My mind is boggled!
Being able to count antenna segments in a photo is often helpful.
It is nice to be able to see details such as that. I probably won’t get the chance for awhile with ongoing field activities for now, but I’m anxious to try out the lens on a tripod with pinned specimens to see what I can do.
Great post, especially re. the role this leaf miner plays. Sometimes it’s just staggering to consider the impacts and interrelationships.
Hi Beau, thanks so much. Although I knew the beetle was rather specialized in its host preference, I wasn’t aware of its potential keystone status until I did the research for this post. I found it fascinating!
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Hi Ted – enjoyed the post and the information. I am especially grateful for the root-word definitions – I have been attempting to learn the meaning of taxonomic names, and have not had much luck. Maybe part of it is that I have been assuming Latin root words, and clearly I should be checking Greek as well.
I don’t know much about macro photography, but I shoot birds regularly, and simply can’t do it without my tripod. It IS a lot to carry. I often get good insect photos with my telephoto lens.
Hi Amber, thank you for the nice comment. Yes, Greek always throws me for a loop as well – for some reason it’s so easy to just assume a Latin root for everything. There are some pretty good internet sites for looking up Greek and Latin roots, and Composition of Scientific Words by Brown has been extremely helpful for me.
I’ve compromised and put a cheap tripod in my truck – not as handy as if I carry it with me, but at least it’s available if I really need it. I think it would be more useful if I had a telephoto lens – right now I’m just trying to assess whether I really want/need telephoto in addition to the two macro lenses that I got. Too many possibilities!
Dear Ted, Perhaps you can settle an argument for me.We were stationed in Panama for three years, I had coconut trees in my yard but the squirrles always ate holes in them. My husband said I was nuts, because there are no squirlles in Panama.I know I am right. Thank you. Sincerly Jayne
Clark 1983 huh? Yes good friend and collecting buddy of mine… It was only several months ago that i collected this species with him. 😀 nice find