host plants

One of North America’s rarer longhorned beetles

/ Ted C. MacRae / 5 Comments

Here are dorsal and lateral views of the only specimen I’ve ever collected of Neoclytus approximatus—one of North America’s most uncommonly encountered longhorned beetles. I collected it on dead Pinus echinata in southeastern Missouri (Carter Co.) way back on June 7, 1987 (just over 34 years ago!), but I believe that is only an incidental record and not a larval host for the species considering that the species has been recorded from primarily the U.S. Great Plains (North Dakota south to Texas, east to Iowa and Missouri, and west to Colorado)—a region mostly devoid of native pines.

Neoclytus approximatus (dorsal view).

What it does breed in remains a mystery. I’ve seen a number of specimens collected in the city of St. Louis, Missouri in the 1930s with U.S.D.A. eugenol-baited Japanese beetle trap, although my own efforts with Japanese beetle traps in St. Louis during the 1980s turned up no specimens. Another Missouri specimen bore a label saying “Monarda” (a genus of flowering plants called “bee balms”)—perhaps referring to the flower of the plant (MacRae 1994). This latter record may suggest the species breeds in herbaceous plants rather than woody plants—which some longhorned beetles are known to do, and its apparent distribution across the Great Plains makes this idea even more tenable.

Neoclytus approximatus (lateral view).

Van Pelt (2007) provides the only other clue to host for the species, citing it “on shrubs” in Big Bend National Park. Until somebody figures out the host for this species, it is liable to remain one of the most elusive species of North American Cerambycidae.

Literature Cited

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].

Van Pelt, A. F. (ed.). 2007. Inventory of insects of Big Bend National Park, Texas. Report to Big Bend National Park, 204 pp.

© Ted C. MacRae 2021

Phocus on Phyllobrotica

/ Ted C. MacRae / 4 Comments

Beetles are often pretty good botanists, and when it comes beetle botanists there are none finer than species in the family Chrysomelidae. Members of this family are commonly called “leaf beetles” because… well, they are usually found on leaves, and with nearly 40,000 known species (and probably many more still unknown) it is one of the largest animal families on the planet! In fact, LeConte & Horn (1883)—the fathers of coleopterology in the United States—surmised that the function of leaf beetles “is to hold the vegetable world in check by destroying … the leaves”!

Here in Missouri we have 351 species and subspecies of leaf beetles (Riley & Enns 1979, 1982), the vast majority of which specialize on a limited range of host plants. Most restrict themselves to feeding on plants within the same family, and some to just a single plant genus or even species! Such specialization does not necessarily make a species rare—western corn rootworm (Diabrotica virgifera) develops almost exclusively on corn (Zea mays), yet it is one of the most abundant leaf beetles in the state, and among non-pest species the dogbane leaf beetle feeds almost exclusively on common dogbane (Apocynum cannabinum) yet is one of our most commonly encountered leaf beetles. There are, however, many other species of leaf beetles in the state that are rarely seen. Almost always they are also extreme host specialists, and there is no better example of this than species in the genus Phyllobrotica.

Eighteen species and one subspecies of Phyllobrotica are known to occur in North America (Riley et al. 2005, Gilbert 2009), of which five have been recorded in Missouri (Riley 1979, Riley & Enns 1979). With one glaring exception (see below), all of the species for which host plants are known restrict their feeding to one of two closely related genera in the mint family (Lamiaceae)—Stachys for most of the western U.S. species, and Scutellaria for most of the non-western U.S. species (Farrell & Mitter 1990). Of the five species in Missouri, only P. limbata has been encountered with any regularity; Riley & Enns (1979) recorded 61 specimens from six widely scattered counties in Missouri, many of them observed on S. ovata or S. lateriflora. A second Missouri species, P. physostegiae, now also is encountered reliably in southwestern Missouri; however, it wasn’t even described until 1979 due to earlier confusion with the enigmatic P. antennata (apparently still known only from the type collected in Tennessee) (Riley 1979). Prior to this, only a handful of specimens were known, three of which had been more recently collected by Rev James Sullivan of St. Louis on plants in the genus Physostegia (also in the mint family). Followup collections turned up large series of beetles on this plant at several locations in southwestern Missouri, and the species was formally described (Riley 1979). Farrell & Mitter (1990) suggest the unusual host is an example of isolated host transfer due to the unusual natural history of P. physostegiae, which along with its sister species is unique in the genus in that it inhabits dry prairie habitats rather than wet bottomlands. Species of Scutellaria inhabiting dry prairies are often annual and more unpredictably available than those inhabiting more mesic habitats, which could have favored broadened host range or shift by the ancestral P. physostegiae population to a related, chemically similar perennial host such as Physostegia (insects typically use volatile plant chemicals, in addition to vision, as informational cues for recognizing their host plants—Visser 1986).

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Phyllobrotica lengi Linell

The three remaining species of Phyllobrotica in Missouri—P. circumdata, P. lengi, and P. nigritarsis—all continue to be among the rarest beetles in the state. The first was never even collected in Missouri until Rev. Sullivan collected 8 specimens—all on S. incana—in a few eastern counties in Missouri in the late 1970s (recorded as “P. discoidea” in Riley & Enns 1979). As far as I can tell, no online images of this species exist, despite it being the most widely distributed species of the genus in North America (Farrell & Mitter 1990, Riley et al. 2003). The second species, P. lengi, was known from Missouri by just four specimens collected in the late 1800s (Riley & Enns 1979) until Rev. Sullivan collected a small series on S. parvula in east-central Missouri in 1988. Like P. circumdata, apparently no online image of this species exists as well—until now… the image above taken of one of the specimens in that small series, which Rev. Sullivan graciously gifted to me shortly after collecting them. The third species, P. nigritarsis, likewise was also known from Missouri by only four specimens—also collected in the late 1800s (Riley & Enns 1979)—until Rev. Sullivan collected a small series in association with S. parvula in east-central Missouri in 1987. Unlike the previous species, however, a single online image does already exist for this species at BugGuide, and the image below—again taken from a specimen in the small series kindly gifted to me by Rev. Sullivan—adds a second.

[Incidentally, both of these photos were taken for a new book by Rev. Sullivan that has just been published—more on that soon!]

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Phyllobrotica nigritarsis Blatchley

Are there additional species of Phyllobrotica in Missouri? Possibly! Phyllobrotica decorata has a known distribution almost as broad as P. circumdata, including several states surrounding Missouri (Illinois, Iowa, and Kansas), and two other eastern U.S. species—P. stenidea and P. vittata—have been collected as far west as Indiana (Riley et al. 2003). There is also the enigmatic P. antennata from Tennessee. Targeting plants in the genus Scutellaria wherever they may be found growing will likely turn up these species, if they occur here, or at least provide additional records for the other species already known from Missouri.

REFERENCES:

Farrell B. D. & C. Mitter. 1990. Phylogenesis of insect-plant interactions: Have Phyllobrotica leaf beetles (Chrysomelidae) and the Lamiales diversified in parallel? Evolution 44(6):1389–1403 [preview].

Gilbert , A. J. 2009. A new species of Phyllobrotica Chevrolat, 1836 (Coleoptera: Chrysomelidae) from California, USA, with notes on the western United States species. The Pan-Pacific Entomologist 84(4) [2008]:269–279 [abstract].

LeConte, J. L. & G. H. Horn. 1883. Classification of the Coleoptera of North America. Smithsonian Miscellaneous Collections 26(507):1–567.

Riley, E. G. 1979. A new species of Phyllobrotica Chevrolat (Coleoptera: Chrysomelidae) from the prairies of southwestern Missouri. The Coleopterists Bulletin 33(3):331–335.

Riley, E. G., S. M. Clark & T. N. Seeno. 2003. Catalogue of Leaf beetles of America North of Mexico. The Coleopterists Society Special Publication No. 1, 290 pp.

Riley, E. G. & W. R. Enns. 1979. An annotated checklist of Missouri leaf beetles (Coleoptera: Chrysomelidae). Transactions of the Missouri Academy of Science 13:53–83.

Riley, E. G. & W. R. Enns. 1982. Supplement to an annotated checklist of Missouri leaf beetles (Coleoptera: Chrysomelidae): new state records and host plant associations. Entomological News 93(1):32–36 [full text].

Visser, J. H. 1986. Host odor perception in phytophagous insects. Annual Review of Entomology 31:121–144 [pdf].

© Ted C. MacRae 2019

“The Botanists Among Us: Host plant specialization in insects”

/ Ted C. MacRae / 4 Comments

It’s been a busy week for me—just two days after doing a presentation on tiger beetles to the Webster Groves Nature Society’s Entomology Group, I gave a talk to the St. Louis Chapter of the Missouri Native Plant Society. As implied by the title, the talk focused on host plant specialization among insects, first covering the major groups of plant-feeding insects and the evolutionary themes involved in adaption to (and away from) plant-feeding, then moving to examples of different types of host plant specificity and highlighting some of the more interesting insects that I’ve encountered (and managed to photograph) over the years.

Like my talk two nights earlier, it was another fun and lighthearted conversation with a highly engaged crowd, and I appreciate the great interest shown by a group that is normally much more focused on plants than on insects. Once again, it was well-attended locally, but for the benefit of those who were not able to attend the meeting in person and that may be interested in this subject, I’ve prepared a PDF version* of the presentation that you can download and peruse at your convenience.

* All content is copyrighted and may not be reproduced or distributed without written consent.

© Ted C. MacRae 2019

A flower visiting jewel beetle that is not an Acmaeodera

/ Ted C. MacRae / 4 Comments

Agrilus muticus

Agrilus muticus LeConte, 1858 | Alabaster Caverns State Park, Woodward Co., Oklahoma

In North America, jewel beetles (family Buprestidae) routinely associated with flowers usually belong to the genus Acmaeodera. Often black with yellow and/or red elytral markings (e.g., A. immaculata, A. macra, A. ornata, A. neglecta, A. tubulus, etc.), these beetles are especially diverse in western North America and bear a striking resemblance to stinging bees and wasps (maintaining the charade even during flight by holding their fused elytra together above the abdomen). A few other less speciose genera (e.g., Anthaxia and Agrilaxia) also regularly visit flowers, but for the most part outside of these genera encounters on flowers are at best incidental.

Agrilus muticus

Adults are associated almost exclusively with flowers of winecup (Callirhoe involucrata).

Of course, exceptions are the rule in biology, and in the genus Agrilus there are few species that are found almost exclusively on flowers. One of these, Agrilus muticus occurs in Texas, Oklahoma, and Kansas and has been found only in the flowers of winecup, Callirhoe involucrata (Fisher 1928). The species is fairly routinely encountered wherever these plants are found in bloom, and I have observed adults in these flowers on numerous occasions feeding on the petals and mating (and see this BugGuide photo of group sex!). While winecup can be presumed to be the larval host, it has never been reared from this (or any other) plant, and in fact I am not aware of anything beyond descriptions and catalogue listings that have been published for the species. I suspect the larvae tunnel within the stem base or main roots of living winecup plants (and, thus, making them more difficult to rear than species associated more typically with dead wood).

Only one other North American Agrilus has been documented routinely visiting flowers. Agrilus blandus is frequently encountered on flowers of Eriogonum, and these plants have also been confirmed as larval hosts (Nelson & Westcott 1976). None of the remaining species of Agrilus in North American are known to routinely visit flowers, and in fact the vast majority of them are associated with woody rather than herbaceous plants. The latter include A. concinnus, which breeds in the base of living Hibiscus (MacRae 2006), and A. malvastri, which is usually found on Sphaeralcea (Fisher 1928), although whether that plant also serves as the larval host remains unconfirmed. It is interesting that most of these non-woody plant hosts (Callirhoe, Hibiscus and Sphaeralcea, but not Eriogonum) all belong to the same plant family—Malvaceae. Plants in this family also serve as known or suspected larval hosts for several species of jewel beetles in the genus Paragrilus—a close relative of the genus Agrilus. Again, these beetles are normally found on the foliage and not on the flowers.

REFERENCE:

MacRae, T. C. 2006. Distributional and biological notes on North American Buprestidae (Coleoptera), with comments on variation in Anthaxia (Haplanthaxia) viridicornis (Say) and A. (H.) viridfrons Gory. The Pan-Pacific Entomologist 82(2):166–199 [pdf].

Nelson, G. H. & R. L. Westcott. 1976. Notes on the distribution, synonymy, and biology of Buprestidae (Coleoptera) of North America. The Coleopterists Bulletin 30(3):273–284 [pdf].

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. [Smithsonian Libraries].

© Ted C. MacRae 2015