Sunset beetles

Acmaeodera immaculata? | vic. Vogel Canyon, Colorado.

Acmaeodera immaculata? (family Buprestidae) | vic. Vogel Canyon, Colorado.

Regular readers of this blog know that I am fond of natural sky backgrounds for insects found during the day on flowers and foliage. Not only does the sky provide a clean, uncluttered background that allows the subject to stand out, it also gives the photo a more appropriate temporal flavor—i.e., photographs of diurnal insects should look like they were taken during the day. It’s a little bit tricky setting the camera to allow flash illumination of the subject while still allowing the sky to register as well, but I find such photographs more pleasing and interesting than those with a jet-black background, typical in flash macrophotography, and far more pleasing than those with a jumble of sticks and weeds cluttered behind the subject. These days my daytime insect photos almost always incorporate a blue-sky background (examples here and here) unless: 1) I actually photographed the subject at night (examples here and here); or 2) I wish to highlight an intensely white or delicately structured subject (examples here and here).

Aulicus sp. | vic. Black Mesa, Oklahoma

Trichodes oresterus? (family Cleridae) | vic. Black Mesa, Oklahoma

But what about in between day and night—specifically, sunset? Incorporating a sunset sky into a flash-illuminated macrophotograph is even trickier than incorporating a blue midday sky because the central problem—low light levels—is magnified. Blue sky photographs challenge the fast shutter speeds and high f-stops usually needed for macrophotographs, but relatively minor adjustments to ISO, shutter speed, and f-stop are usually sufficient to allow the sky to register while still being able to maintain depth of field and minimize motion blur. At sunset, however, because there is much less illumination of the sky, more aggressive settings are often required to allow the sky to register on the camera sensor—settings that can sometimes result in too much motion blur or insufficient depth of field. These problems can be mitigated to some degree with the use of a tripod (and very cooperative subjects), but for dedicated “hand-held” enthusiasts like myself this is not an option. Why bother? Because the results can be spectacular! The setting sun often creates stunning colors not seen at other times of the day and offer a change of pace from blue skies, which, like black backgrounds, can start looking rather monotonous if used exclusively in one’s portfolio.

Linsleya convexa | vic. Vogel Canyon, Colorado

Linsleya convexa (family Meloidae) | vic. Vogel Canyon, Colorado

The photos featured in this post were taken during several sunsets on a trip earlier this past summer through Colorado and Oklahoma. I especially like the jewel beetle (Acmaeodera immaculata?) photograph—technically it has good focus and depth of field and a pleasing composition, but I really like the color coordination between the beetle, flower, and sky. The checkered beetle (Trichodes oresterus?) photograph is also very pleasing, especially the detail on the beetle, although the color of the sky is only somewhat different than a more typical daytime blue. The blister beetle (Linsleya convexa) photograph is probably the most problematic technically due to slight motion blur and being slightly off-focus at the eye—not surprising since of the three this photo had the lowest light conditions. However, the color contrast between the sky and subject make this a nevertheless striking image.

If you have experience with ambient light backgrounds in flash macrophotography, your comments on approaches you’ve taken to deal with reduced light situations will be most welcome.

© Ted C. MacRae 2014

Seminar on Oklahoma’s Glass Mountains

Earlier this week I gave a seminar to the Entomology Group of the Webster Groves Nature Study Society. Founded in 1920 and known locally as “WGNSS”, the organization seeks “to stimulate interest in nature study on the part of adults and children, to cooperate with other organizations in nature study, and to encourage amateur research in the natural science.” I’ve been an active member in the society’s Entomology Group since the early 1980s, and for almost five years now I have also served as editor for the society’s newsletter, Nature Notes (see this archive of recent issues). Occasionally they invite me to talk—sometimes to just the Entomology Group and other times to the Society as a whole—about my entomological exploits. This time I chose to focus on my several visits to the Glass Mountains in northwestern Oklahoma over the past few years, which readers of this blog may remember has been the source of an inordinate number of new state records and other significant finds for the beetles I study. The presentation provided an overview of the insects I’ve encountered during these visits, and for those who might be interested a PDF version of the presentation is posted here. 

Natural History of Oklahoma’s Glass Mountains…

Copyright © Ted C. MacRae 2014

What was that insect?

Yesterday I posted an identification challenge of a different sort. The main subject in the photo was a jewel beetle (family Buprestidae), but there was also another insect in the photo—a small parasitic wasp sitting on the branch below the beetle. Some of you saw it—Charley Eiseman was the first and correctly guessed it was a member of the family Encyrtidae, earning 5 pts, and Wikispecies editor gets 5 pts for further identifying it as a member of the genus Metaphycus. Honestly, I took several shots of the beetle and never saw the wasp until I examined the photograph during processing. I’m not certain, but I think the small object next to the wasp could be a scale insect (family Coccidae), which are known hosts of Metaphycus spp.

Of course, there is still the jewel beetle, and it wouldn’t be fair for me to award points for the wasp but not the beetle. Heath gets 5 pts for first identifying the beetle in the genus Agrilus; however, nobody was able to identify the species as A. granulatus—commonly associated with cottonwood and poplar (Populus spp.) across North America. Since Charley was the only person to mention both the beetle and the wasp, I’m going to give him a tie-breaking bonus point and declare him the challenge winner.

Populations of A. granulatus have been assigned to several subspecies—the beetle shown here (photographed June 2013 at Beaver Dunes, Oklahoma) represents the nominate form—restricted to the U.S. east of the Rocky Mountains, where it breeds in native eastern cottonwoods (P. deltoides) and introduced Lombardy poplars (P. nigra var. ‘Italica’). Agrilus granulatus is often confused in collections with A. quadriguttatus, but that species is associated with willow (Salix spp.) and can be further distinguished by the less dense pubescence of the lower face not obscuring the surface; the pronotum with the lateral margins evenly rounded and not strongly sinuate at the base, the median channel less distinct, and the lateral depressions scarcely pubescent; and the elytra more gradually narrowed posteriorly with the tips more acutely rounded and more coarsely serrulate and the pubescent spots less distinct (Fisher 1928).

Here are a few more photographs of the jewel beetle (without the wasp):

Agrilus granulatus granulatus on Populus deltoides | Beaver Dunes, Oklahoma

Agrilus granulatus granulatus on Populus deltoides | Beaver Dunes, Oklahoma

Agrilus granulatus granulatus on Populus deltoides | Beaver Dunes, Oklahoma

Agrilus granulatus granulatus on Populus deltoides | Beaver Dunes, Oklahoma

Agrilus granulatus granulatus on Populus deltoides | Beaver Dunes, Oklahoma

Agrilus granulatus granulatus on Populus deltoides | Beaver Dunes, Oklahoma

REFERENCE:

Fisher, W. S.  1928. A revision of the North American species of buprestid beetles belonging to the genus Agrilus.  U. S. National Museum 145, 347 pp.

Copyright © Ted C. MacRae 2014

Pop! goes the beetle

Alaus oculatus (eyed elater) | Beaver Dunes State Park, Oklahoma

Alaus oculatus (eyed elater) | Beaver Dunes State Park, Oklahoma

Last June while collecting beetles from cottonwood trees at Beaver Dunes State Park, Oklahoma, I came across one of my favorite beetles—Alaus oculatus, or eyed elater (family Elateridae, or click beetles). Large by click beetle standards, the most striking feature of eyed elaters is, of course, their false eye spots, which are not eyes at all but patches of pubescence—black surrounded by a narrow ring of white—intended to look like eyes and located prominently on the prothorax rather than the head. A handful of related species are also found in various parts of the U.S., all of which exhibit variations on this same eye spot theme. Undoubtedly these spots serve to frighten would-be predators, much like the false eye spots on the thorax of many lepidopteran caterpillars. The true eyes, of course, are much smaller and are located on the head in front of the “false eyes.” In contrast to the prominently visible eye spots, pubescence on the rest of the body seems to function in cryptic coloration. The mottled patterning blends in with the bark of trees where these beetles usually hang out for effective concealment.

Look into my eye(spot)s!

Look into my eye(spot)s!

If either of those first two lines of defense don’t work, the beetles exhibit “thanatosis” by lying still with legs and antennae appressed to the body to fool the would-be predator into thinking that they are already dead.

A ventral look at the clicking mechanism between the pro- and mesosterna.

Adults exhibit “thanatosis” (play dead)  when disturbed.

Their most remarkable defensive behavior, however, is their ability to snap or “click” their bodies with enough force to free themselves from the grasp of a novice predator (or careless entomologist). The click is produced by a large prosternal spine and mesosternal notch on the beetle’s underside. To click, the beetle arches back its head and pronotum to retract the spine from the notch cavity, the tip of which is then pressed against the edge of the notch. Muscles within the thorax contract, storing elastic energy, and as the flexible hinge between the pro- and mesothoraces moves, the spine slides until its tip passes over the edge of the notch, releasing the elastic energy stored in the thoracic musculature and snapping the spine back into the notch cavity with enough force to produce an audible click.

A large spine on the prosternum fits into a groove on the mesosternum.

A large spine on the prosternum fits into a groove on the mesosternum.

This clicking ability also comes in handy if the beetle frees itself from the grasp of a predator and lands on its back. While the beetle’s legs are too short to right itself, its click is capable of launching the beetle high into the air. By tumbling while in the air, the beetle has a 50% chance of landing on its feet (thus, several attempts may be required). When jumping from a hard surface, the beetle is actually capable of launching itself to a height that is several times its body length and can tumble several times while in the air. This raises an interesting question, since theoretically an elevation of only one body length and half of a body revolution are all that is needed for an upside-down beetle to right itself. The power of the click, thus, grossly exceeds the minimal requirement for righting, yet the beetles seem incapable of moderating the force of the click. Furthermore, the 50% probability of landing suggests that they are also incapable of controlling the orientation of their body during the jump and landing. Did the clicking mechanism initially evolve to combat the grasp of predators and was then co-opted for use in jumping, or was the ability to jump the selective pressure that drove its evolution?

Locked and loaded—the mechanism is primed for the click.

Locked and loaded—the mechanism is primed for the click.

Ribak & Weihs (2011) used biomechanical analyses with Lanelater judaicus to support the idea that the click evolved primarily as a mechanism for vertical jumping. They reason that the excessive vertical distance of the jumps ensures sufficient height when jumping from soft substrates such as foliage or loose soil. A followup study evaluating the effect of natural substrates (Ribak et al. 2012) found that jump height was dramatically reduced (by ~75%) when the beetles jumped from leaves that covered approximately half of the study site and that the reduction in jump height was directly correlated with the amount of work absorbed by the substrate. This provides further evidence that the beetles do not moderate their jumping force and instead simply aim to jump “as high as possible” and rely on random chance for landing back on their feet.

After clicking, the spine returns to its resting position out of the groove.

After clicking, the spine returns to its resting position within the groove.

REFERENCE:

Ribak, G., S. Reingold & D. Weihs. 2012. The effect of natural substrates on jump height in click-beetles. Functional Ecology 26(2):493–499 [abstract].

Ribak, G. & D. Weihs. 2011. Jumping without using legs: The jump of the click-beetles (Elateridae) is morphologically constrained. PLoS ONE 6(6):e20871. doi:10.1371/journal.pone.0020871 [full text].

Copyright © Ted C. MacRae 2014

Hairy milkweed beetle

Across the Great Plains of North America, sand dune fields dot the landscape along rivers flowing east out of the Rocky Mountains. Formed by repeated periods of drought and the action of prevailing south/southwest winds on alluvium exposed by uplifting over the past several million years, many of these dunes boast unique assemblages of plants and animals adapted to their harsh, xeric conditions. Some are no longer active, while others remain active to this day. Among the latter is Beaver Dunes in the panhandle of northwestern Oklahoma.

Beaver Dunes, Oklahoma

Beaver Dunes State Park, Beaver Co., Oklahoma

As I explored the more vegetated areas around the perimeter of the dunes, I spotted the characteristically hairy, fleshy, opposite leaves of Ascelpias arenaria. Known also as “sand milkweed,” this plant is associated with sand dunes and other dry sandy soil sites throughout the central and southern Great Plains. I always give milkweeds a second look whenever I encounter them due to the association with them by longhorned beetles in the genus Tetraopes. It wasn’t long before I spotted the black antennae and red head of one of these beetles peering over one of the upper leaves from the other side.

Tetraopes pilosus on Asclepias arenaria

Tetraopes pilosus on Asclepias arenaria | Beaver Dunes State Park, Oklahoma

This was no ordinary Tetraopes, however. Its large size, dense covering of white pubescence, and association with sand milkweed told me immediately that this must be T. pilosus (the specific epithet meaning “hairy”). Like its host, this particular milkweed beetle is restricted to Quaternary sandhills in the central and southern Great Plains (Chemsak 1963), and also like its host the dense clothing of white pubescence is presumably an adaptation to prevent moisture loss and overheating in their xeric dune habitats (Farrell & Mitter 1998).

Tetraopes pilosus

Species of Tetraopes have the eyes completely divided by the antennal insertions—thus, “four eyes.”

Tetraopes is a highly specialized lineage distributed from Guatemala to Canada that feed as both larvae and adults exclusively on milkweed (Chemsak 1963). Larval feeding occurs in and around the roots of living plants, a habit exhibited by only a few other genera of Cerambycidae but unique in the subfamily Lamiinae (Linsley 1961). Milkweed plants are protected from most vertebrate and invertebrate herbivores by paralytic toxins, commonly termed cardiac glycosides or cardenolides. However, a few insects, Tetraopes being the most common and diverse, have not only evolved cardenolide insensitivity but also the ability to sequester these toxins for their own defense. Virtually all insects that feed on milkweed and their relatives have evolved aposematic coloration to advertise their unpalatability, and the bright red and black color schemes exhibited by milkweed beetles are no exception.

Species of the genus Tetraopes are characterized by the completely divided eyes.

Adult beetles, like the leaves of their hosts, are clothed in white pubescence.

As  noted by Mittler & Farrel (1998), variation in coloration among the different species of Tetraopes may be correlated with host chemistry. Milkweed species vary in toxicity, with more basal species expressing simpler cardenolides of lower toxicity and derived species possessing more complex and toxic analogs. Most species of Tetraopes are associated with a single species of milkweed, and it has been noted that adults of those affiliated with less toxic milkweeds on average are smaller, have less of their body surface brightly colored, and are quicker to take flight (Chemsak 1963, Farrell & Mitter 1998). Thus, there seems to be a direct correlation between the amount of protection afforded by their host plant and the degree to which the adults advertise their unpalatability and exhibit escape behaviors. Asclepias arenaria and related species are the most derived in the genus and contain the highest concentrations of cardenolides. In fact, they seem to be fed upon only by Tetraopes and monarchs while being generally free from other more oligophagous insect herbivores such as ctenuchine arctiid moths and chrysomelid beetles that feed on less derived species of milkweed (Farrell & Mitter 1998). Accordingly, T. pilosus is among the largest species in the genus and has the majority of its body surface red. Also, consistent with it being more highly protected than others in the genus, I noted virtually no attempted escape behavior as I photographed this lone adult.

Asclepias arenaria

Asclepias arenaria (sand milkweed) growing at the base of a dune.

In addition to metabolic insensitivity to cardenolides, adult Tetraopes also exhibit behavioral adaptations to avoid milkweed defenses (Doussard & Eisner 1987). The milky sap of milkweed is thick with latex that quickly dries to a sticky glue that can incapacitate the mouthparts of chewing insects that feed upon the sap-filled tissues. Adult Tetraopes, however, use their mandibles to cut through the leaf midrib about a quarter of the way back from the tip. This allows much of the sticky latex-filled sap to drain from the more distal tissues, on which the beetle then begins feeding at the tip. Leaves with chewed tips and cut midribs are telltale signs of feeding by adult Tetraopes.

REFERENCES:

Chemsak, J. A. 1963. Taxonomy and bionomics of the genus Tetraopes (Coleoptera: Cerambycidae). University of California Publications in Entomology 30(1):1–90, 9 plates.

Doussard, D. E. & T. Eisner. 1987. Vein-cutting behavior: insect counterploy to the latex defense of plants. Science 237:898–901 [abstract].

Farrell, B. D. & C. Mitter. 1998. The timing of insect/plant diversification: might Tetraopes (Coleoptera: Cerambycidae) and Asclepias (Asclepiadaceae) have co-evolved? Biological Journal of the Linnean Society 63: 553–577 [pdf].

Linsley, E.G. 1961. The Cerambycidae of North America. Part 1. Introduction. University of California Publications in Entomology 18:1–97, 35 plates.

Copyright © Ted C. MacRae 2013

Why did it take 30 years to collect these beetles?

Poecilonota cyanipes

Poecilonota cyanipes (eastern poplar jewel beetle) | Beaver Dunes State Park, Oklahoma

This is the best known of the American species of Poecilonota, and the one most commonly collected east of the Rocky Mountain.—Evans (1957)

I’ve been interested in insects since I was a kid, but I didn’t really become a dedicated coleopterist until after I’d finished graduate school and started working as a field entomologist with the Missouri Department of Agriculture. It was a perfect job for a young entomologist with a bent for collecting—being outside all day inspecting nursery stock and driving the back roads checking insect traps. It wasn’t long before I found myself focusing on wood-boring beetles, due initially to their horticultural importance but eventually to their astounding diversity and intrinsic beauty. So began my formal survey of the families Buprestidae and Cerambycidae in Missouri, and I spent the next eight years collecting them in all corners of the state and examining every insect collection, public and private, that I could find that might contain Missouri representatives of these families. In the end, I documented a cool 350 species and subspecies in the two families combined, more than a fifth of which represented new state records (MacRae 1991, 1994).

Poecilonota cyanipes

The specific epithet ‘cyanipes‘ refers to the blue feet

One species, however, that I had expected to find almost completely eluded me. This, despite the quote above by Evans (1957) in his revision of the genus Poecilonota in North America. Although it had been recorded from much of North America east of the Rocky Mountains in association with poplars (Populus spp.) and willows (Salix spp), I never actually encountered P. cyanipes in the field and found just two specimens labeled simply “Mo” in the insect collection at the University of Missouri in Columbia. This puzzled me, as I had beaten countless branches of cottonwood (Populus deltoides) and willow in search of this species and found many of the other known poplar/willow associates. I had even already collected two specimens of its much rarer congener, P. thureura, off of a redbud tree at the entrance to the Entomology Building on campus while still in graduate school!

Poecilonota cyanipes

This species can be recognized by its coppery color and elongate, distinctly reddish elytral apices,

As is often the case, good comes to those who wait, and I’ve finally gotten my chance during the past two seasons to encounter this species in numbers—last year as prey taken from nest sites of the buprestid-specialist crabronid wasp, Cerceris fumipennis, and this past June on cottonwood trees in northwestern Oklahoma at Beaver Dunes State Park. The individual in these photos was the first one I found—beaten from the lower branch of a small, living cottonwood exhibiting significant branch dieback, and over the course of the next two days I managed to beat close to three dozen specimens from the small, stunted cottonwoods that dotted the park. I suspect that the combination of good timing—buprestids of many types were common on a number of woody plant species in the area—and susceptible hosts with abundant branch dieback due to protracted drought conditions over the past few years was the reason I was able to find so many of the beetles. A perfect storm for wood-boring beetles, so to speak!

Poecilonota cyanipes

The non-angulate pronotal sides distinguish this species from another eastern species, P. ferrea.

As suggested above, larvae of this species are associated exclusively with dead or dying branches of Populus and Salix (both in the family Salicaceae), often in association with galls made previously by other species of wood-boring beetles, e.g., Saperda concolor in poplar (Knull 1920) and Agrilus criddlei in willow (Wellso et al. 1976). In fact, with one exception (P. viridicyanea on Chilopsis linearis) all members of the genus seem to be associated exclusively with plants in these two genera. However, in addition to these plants, Nelson et al. (2008), in their catalogue of the Buprestidae of the U.S. and Canada, also included black locust (Robinia pseudoacacia) in the family Fabaceae as a larval host for P. cyanea. I am convinced that this record represents at best a mere incidental adult association, and there are other examples of such in the catalogue (the final preparation of which was completed after the untimely death of the senior author). This is unfortunate, since erroneous records in such ‘standard’ references tend to be propagated in subsequent literature, which already seems to have happened in the case of black locust as a larval host for P. cyanipes (Paiero et al. 2012).

REFERENCES:

Knull, J. N. 1920. Notes on Buprestidae with description of a new species (Coleop.). Entomological News 31(1):4–12 [BioStor].

MacRae, T. C. 1991. The Buprestidae (Coleoptera) of Missouri. Insecta Mundi5(2):101–126 [pdf].

MacRae, T. C. 1994. Annotated checklist of the longhorned beetles (Coleoptera: Cerambycidae and Disteniidae) known to occur in Missouri. Insecta Mundi 7(4) (1993):223–252 [pdf].

Nelson, G. H., G. C. Walters, Jr., R. D. Haines, & C. L. Bellamy.  2008.  A Catalogue and Bibliography of the Buprestoidea of American North of Mexico.  Coleopterists Society Special Publication No. 4, The Coleopterists Society, North Potomac, Maryland, 274 pp. [description].

Paiero, S. M., M. D. Jackson, A. Jewiss-Gaines, T. Kimoto, B. D. Gill & S. A. Marshall. 2012. Field Guide to the Jewel Beetles (Coleoptera: Buprestidae) of Northeastern North America. 1st Edition. Canadian Food Inspection Agency, 411 pp. [pdf].

Wellso, S. G., G. V. Manley & J. A. Jackman. 1976. Keys and notes on the Buprestidae (Coleoptera) of Michigan. The Great Lakes Entomologist 9(1):1–22.

Copyright © Ted C. MacRae 2013

Party on a pin oak

In September 2012 while collecting in western Oklahoma (Weatherford) I came across this interesting scene. It had been exceedingly dry in the area, and because of this few insects were out and about in the small city park that I stopped by to check for the presence of tiger beetles. I had nearly completed my circuit of the park when I came upon a moderate-sized pin oak (Quercus palustris) tree and noticed something on the lower trunk:

Six insect species representing five families in four orders share a sap flow.

Six insect species representing five families in four orders share a sap flow on the trunk of a pin oak.

No less than six insect species representing four orders were seen all huddled together at a darkly stained sap flow. This could be the result of slime flux, a bacterial disease that usually affects deciduous hardwoods that are under stress and results in darkly stained weeps on the trunk that are known to be attractive to a variety of insects. At the center sat a green June beetle (Cotinis nitida) and three bumble flower beetles (Euphoria inda)—all in the family Scarabaeidae (subfamily Cetoniinae). Covering the scarab beetles were half a dozen Texas Tawny Emperor (Asterocampa clyton texana) butterflies (family Nymphalidae, or Brushfooted Butterflies), and milling around the perimeter was a velvet ant (Dasymutilla creusa, I believe) in the family Mutillidae, an apparent flesh fly (family Sarcophagidae), and a true ant (family Formicidae). I guess this would be the equivalent to a watering hole in Africa with a lion, a hyena, a baboon, three vervet monkeys and six zebras all crouched shoulder-to-shoulder at its edge.

Euphoria sepulchralis feeds on a sap flow higher up on the trunk.

Euphoria sepulchralis feeds on a sap flow higher up on the trunk.

Further up on the trunk, yet another species of scarab beetle, a dark flower scarab (Euphoria sepulchralis) was found feeding on a smaller sap ooze. Unlike the diverse aggregation of insects on the lower ooze, this guy had managed to keep the ooze all to himself.

Cotinus nitidus | Weatherford, Oklahoma

Cotinis nitida | Weatherford, Oklahoma

Green June beetles, especially, are known for their feeding on sap oozes. The beetles are actually attracted to the odors caused by fermentation of the sap rather than the sap itself. It has been reported that the presence of alcohol in fermenting sap can affect the behaviour of insects that feed upon it, causing them to act “stupid and lethargic.” I did not see any such behavior, but I did notice that the insects were not at all skittish and loath to leave the sap.

Copyright © Ted C. MacRae 2013