Month: July 2015

Redux: Now you see me…

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Chalcophora virginiensis

Chalcophora virginiensis (Drury, 1770) | vic. Calico Rock, Arkansas

…now you don’t!

Chalcophora virginiensis

Chalcophora virginiensis (Drury, 1770) | vic. Calico Rock, Arkansas

Chalcophora virginiensis (Drury, 1770) is the largest jewel beetle (family Buprestidae) in eastern North America. This beetle is also known as the “sculptured pine borer”, and its easy to see why—its hyper-sculptured, shiny metallic body glitters like a jewel in the sunlight! This feature is typical of many species in the family and, in fact, is the source of the family’s other common name—metallic wood boring beetles.

Such dramatic sculpturing and coloration makes cabinets of jewel beetle specimens among the most beautiful in any museum, and for those who have only seen these beetles as pinned specimens in cabinets it can be hard to imagine what purpose such appearance serves. In its native habitat, however, on native host plants, the reason becomes clear. Rather than conspicuous and easily seen, such coloration actually helps the beetle to blend in with its environment and become almost invisible. Measuring well over an inch in length and possessing no other way of defending itself by biting, stinging, or even just tasting bad, these beetles would be a more than healthy snack for almost any avian or reptilian predator, and going about their activities during the day right under the noses of all these visually based predators makes finding mates and oviposition sites an even riskier proposition. For them, the best way to beat a visual predator is to become… invisible! The two photos above show just how dramatic a difference the substrate plays in allowing these beetles to practice their disappearing act. Land on the trunk of a dead or dying pine tree, its aged bark flaked and graying, and the sculpturing and coloration are a perfect match. Land, however, on a healthy tree, its resin-filled bark bright and full of color, and it suddenly becomes a sitting duck. It’s in the beetle’s best interest to be good at telling the difference between thrifty and unhealthy trees, which they do by “smelling” volatile chemicals emitted by trees under stress.

Those interested in more information on this species and its close relatives may wish to consult the recent review of the genus in North America by Maier & Ivie (2014) (see my review of this excellent paper here).

REFERENCE:

Maier, C. A. & M. A. Ivie. 2013. Reevaluation of Chalcophora angulicollis (LeConte) and Chalcophora virginiensis (Drury) with a review and key to the North American species of Chalcophora Dejean (Coleoptera: Buprestidae). The Coleopterists Bulletin 67(4):457–469 [abstract].

© Ted C. MacRae 2015

Spring beetles on Coreopsis flowers

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Abby Lee, Ryan Fairbanks, Stephen Penn atop a rhyolite glades

The WGNSS Entomology Group takes in the view of rhyolite glades from atop Hughes Mountain.

Each spring the Entomology Group of the Webster Groves Nature Study Society takes a field trip to one of the many natural areas outside of the St. Louis area. This year the destination was Hughes Mountain Natural Area, about 75 miles SSW of St. Louis in Washington Co. I especially looked forward to going there this spring, as my last visit to the area was close to 20 years ago. Despite the long absence, I vividly recalled the spectacular vistas from atop the mountain of rhyolite and the diversity of unique plants and insects in the igneous glades that flanked its slopes. When we arrived, we found the glades ablaze with spring wildflowers in full bloom, the most prominent of which was lance-leaved coreopsis (Coreopsis lanceolata). As one of the so-called “yellow composites”, coreopsis is a favored source of pollen and nectar for a variety of insects, including beetles and especially the jewel beetles that I find so interesting.

Acmaeodera neglecta

Acmaeodera neglecta Fall, 1899

Species in the genus Acmaeodera are incredibly diverse in the southwestern U.S. (nearly half of the ~150 species/subspecies known from the U.S. occur in Arizona), where they are usually encountered on a variety of flowers. It is my opinion that the adult beetles mimic small bees, especially in flight by virtue of their fused elytra that do not separate during flight as in most other beetles and thus results in a profile resembling that of a small sweat bee (family Halictidae). The diversity of Acmaeodera drops off considerably in the eastern U.S., with only three species occurring broadly in the area. Missouri is a bit luckier than most eastern states, as two additional species found primarily in the south-central U.S. also occur here (MacRae 1991). One of these is Acmaeodera neglecta Fall, 1899. This tiny species (adults measure only 4–6 mm in length) is very similar to the much more common and widespread A. tubulus (Fabricius, 1801) (see photos here), and in fact its resemblance to that species is so great that it remained unreported from Missouri until Nelson (1987) recognized it among material that I had collected and sent to him during my early collecting days. Acmaeodera neglecta can be distinguished from A. tubulus by the elytra with slightly larger punctures and duller surface and the spots usually longitudinally coalesced into an irregular “C”-shaped marking on each side. I find this species most often in glade habitats.

Acmaeodera ornata

Acmaeodera ornata (Fabricius, 1775)

Acmaeodera ornata (Fabricius, 1775) is more widespread than A. neglecta (although not nearly so commonly encountered as A. tubulus). This handsome species is distinctly larger than A. tubulus and A. neglecta, usually around 8-11 mm in length, and has a broader, more flattened appearance with a distinct triangular depression on the pronotum. The elytra have a bluish cast rather than the bronzy sheen of A. tubulus and A. neglecta, and the spots on the elytra are smaller, more numerous, and more of a creamy rather than yellow color. No other species in the eastern U.S. can be confused with it, although there is a very similar species (A. ornatoides Barr, 1972) that occurs in Oklahoma and Texas. I have encountered this species numerous times on a variety of flowers in Missouri but have never managed to rear it, and in fact larval hosts remain unknown with the exception of one very old (and unreliable) report of the species breeding in hickory (Carya) and black-locust (Robinia).

Valgus canaliculatus

Valgus canaliculatus (Olivier, 1789)

As a general rule, beetles in the family Scarabaeidae don’t visit flowers—species in the subfamily Cetoniinae being a significant exception. This tiny representative of the subfamily, Valgus canaliculatus (Olivier, 1789), is no larger than the Acmaeodera neglecta adult above by length, although the body is broader and strongly flattened. This species is a representative of the tribe Valgini, one of only two tribes in the family that possess dorsal and ventral scale-like setae (the unrelated tribe Hopliini, or monkey beetles, being the other) (Jameson & Swoboda 2005). It has been suggested that the setae might play a role in crysis or adaptive coloration, and even more interesting is the association of most New World species with termites. Eggs are laid in termite galleries and the larvae feed on the wood within the galleries, but it remains unclear whether the termophily is obligatory or the beetles are simply taking advantage of the stable environment and accessible food source offered by termite colonies. Like other species in the subfamily, the adults are fond of flowers; however, only male valgines visit flowers, using specially modified, brush-like mouthparts to lap up nectar. As far as has been determined, the males do not feed on pollen.

Valgus canaliculatus

Note the flattened, scale-like setae covering both the dorsal and ventral surfaces as well as the legs.

REFERENCES:

Fall, H. C.  1899. Synonpsis of the species of Acmaeodera of America, north of Mexico. Journal of the New York Entomological Society 7(1):1–37 [pdf].

Jameson, M. L. & K. A. Swoboda. 2005. Synopsis of scarab beetle tribe Valgini (Coleoptera: Scarabaeidae: Cetoniinae) in the New World. Annals of the Entomological Society of America 98(5):658–672 [pdf].

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

Nelson, G. H. 1987. Additional notes on the biology and distribution of Buprestidae (Coleoptera) in North America, II.   The Coleopterists Bulletin 41(1):57–65 [pdf].

© Ted C. MacRae 2015

A cicada that snaps, crackles, and pops!

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Last summer during a collecting trip through the western Great Plains, field partner Jeff Huether and I made a quick stop in the foothills of the Rocky Mountains just a few miles north of the Colorado/New Mexico state line. Most of the woody vegetation turned out to be New Mexico locust (Robinia neomexicana), which can be a good host for certain species of jewel beetles and longhorned beetles, and since it was mid-late June the timing was also right (assuming there had been good rains in the area). We began beating branches, picking up regular numbers of small longhorned beetles in the genus Sternidius and jewel beetles in the genus Agrilus—nothing unexpected. As I was beating I happened to notice a cicada sitting in a branch in a nearby tree. Usually I don’t see cicadas until they take flight after I unknowingly approach them—more often than not also letting out a metallic screech as they take flight if they are male, and even if I do see them beforehand I rarely am able to get close enough to attempt capture, much less photography. Perhaps the morning temps still had not risen to a point sufficient for the more active behaviors with which cicadas are usually associated.

Platypedia putnami

Platypedia putnami | Las Animas Co., Colorado

The slender, hairy, black body, orange highlights and pronotal collar, and black eyes identify this as a member of the genus Platypedia, and while the genus is large—21 species and four subspecies in western North America (Sanborn & Phillips 2013), its gestalt and occurrence in south-central Colorado make P. putnami the likely choice. Cicadas, of course, are famous for their singing abilities, which is most commonly accomplished through the use of structures at the base of the male abdomen called timbals (or ‘tymbals’). These paired, ribbed membranes make a loud click when buckled, and the male uses musculature to rapidly and rhythmically buckle/unbuckle the timbals to produce their characteristic song (Young & Bennet-Clark 1995). Cicadas of the genus Platypedia, however, belong to a group of genera that have lost the ability to produce sound through timbal organs, instead communicating through an alternate mechanism of sound production called crepitation where the wings are snapped together above the body or banged against the body or on vegetation (Sanborn and Phillips 1999). (Think of the snapping sound that some grasshoppers make as they fly, which is produced by the same mechanism.) You can hear the sound (I can’t really call it a ‘song’) and see a collection of videos of these cicadas at Cicada Mania.

Of course, replacement of one sound production mechanism by another begs the question—is there a selective advantage to sound production by crepitation over timbals? The fact that females also produce sound by crepitation hints at one possible advantage—2-way communication between males and females may provide another mechanism for minimizing the chance of interspecies mate selection, in contrast to the one-way communication (from males to females) that occurs in species that use timbal organs. It is also possible that crepitation is metabolically more efficient than timbal singing, although experimental comparisons of the energetic cost of crepitation versus timbal singing in cicadas are lacking (Sanborn & Phillips 1999).

REFERENCES:

Sanborn, A. F. & P. K. Phillips. 1999. Analysis of acoustic signals produced by the cicada Platypedia putnami variety lutea (Homoptera: Tibicinidae). Annals of the Entomological Society of America 92:451–455 [pdf].

Sanborn, A. F. & P. K. Phillips. 2013. Biogeography of the cicadas (Hemiptera: Cicadidae) of North America, north of Mexico. Diversity 5(2):166–239 [abstract, pdf].

Young, D. & H. C. Bennet-Clark. 1995. The role of the tymbal in cicada sound production. The Journal of Experimental Biology 198:1001–1019 [pdf].

© Ted C. MacRae 2015

Why is this male carrion beetle “biting” one of the female’s antennae?

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American carrion beetles (Necrophila americana) aggregating at sap flow on the trunk of an oak (Quercus sp.) tree.

American carrion beetles (Necrophila americana) aggregation at sap flow on trunk of oak (Quercus sp.) tree.

Earlier this spring I came upon an interesting aggregation of insects at a sap flow at the base of the trunk of a large oak (Quercus sp.) tree. Sap flows are famous for the diversity of insects that are attracted to them (e.g., see my previous post, Party on a pin oak), although the mix of species present can vary from sap flow to sap flow. In this case, the majority of insects present were American carrion beetles (Necrophila americana)¹ (order Coleoptera, family Silphidae), a species encountered much more often on animal carcasses (in fact, the genus name literally translates to “attracted to corpses“) but also occasionally attracted to sap flows (Evans 2014). This is not surprising to me, as I have seen adults regularly in the fermenting bait traps (Champlain & Knull 1932) that I have set out over the years (although I have been unable to find any reference to such attraction in the literature). I had never seen such an aggregation of these beetles before or even yet had the chance to photograph them (although I have photographed its Ceti Eel-like larva), so I paused to setup the camera and take a few photographs.

¹ Not to be confused with the federally endangered American burying beetle (Nicrophorus americanus).

Necrophila americana mating pair.

Necrophila americana mating pair.

Among the many single adults present was a mating pair, which I selected as my subjects. As I was photographing the pair, I noticed the male had a firm grasp of one of the female’s antennae within his mandibles. As I watched them through the lens, I saw the male suddenly release his hold of the female’s antenna, move backward on top of her, and begin using his own antennae to stroke her pronotum (sadly I was unable to snap a photograph at that time). As suddenly as he had released it, the male moved forward and grabbed hold of the female’s antenna once again. It seemed unlikely to me that this represented an act of aggression, but instead must be an important part of their courtship behavior. The female, for her part, did not seem to be bothered too much by the grasping and continued to slowly lumber about around the sap flow as the male went through his routine under my voyeuristic watch.

The male has a firm grasp of the female's antenna.

The male has a firm grasp of the female’s antenna.

Intrigued by this behavior, I searched for other photos of mating/coupled carrion beetles—easy to do considering the many pages of photographs of this species at BugGuide. While the great majority of those photos are of individual beetles, I found this photo and this one of coupled pairs, each also clearly showing the male firmly grasping one of the female’s antennae with his mandibles. Neither photo makes mention of the antennal grasping, but a little further searching did turn up this YouTube video of coupled American carrion beetles, again clearly showing the male grasping of the female’s antenna and even leading the videographer to comment, “Disturbingly, it even appears that this male is threatening to lop off the female’s left antenna if she refuses to mate!” Of course, retribution seems not to be a common behavior among insects, and in looking into this further I found a short note by Anderson (1989) in which the behavior is recorded not only for N. americana but also another silphid, Oiceoptoma noveboracense. Apparently mating actually occurred during the time the male had released his hold of the female’s antenna and was stroking her pronotum with his antennae. He further noted that the antennal grasping behavior continues until eggs and larvae are present at a carcass, at which time it is no longer observed. This suggests that the behavior represents an especially proactive form of “mate guarding” by which males actively ensure their paternity of the offspring of the particular female with which they were mating.

REFERENCES:

Anderson, R. S. 1989. Potential phylogenetic utility of mating behavior in some carrion beetles (Coleoptera: Silphidae: Silphinae). The Coleopterists Bulletin 43(1):18 [pdf].

Champlain, A. B. & J. N. Knull. 1932. Fermenting bait traps for trapping Elateridae and Cerambycidae (Coleop.). Entomological News 43(10):253–257.

Evans, A. V. 2014. Beetles of Eastern North America. Princeton University Press, Princeton, New Jersey, 560 pp. [Google Books].

© Ted C. MacRae 2015