Chrysobothris eriogoni Westcott

Westcott, Richard L., 2005, A new species of Chrysobothris Eschscholtz from Oregon and Washington, with notes on other Buprestidae (Coleoptera) occurring in the United States and Canada, Zootaxa 1044, pp. 1-15 : 2-7

Chrysobothris eriogoni Westcott , new species

( Figs. 1–6 )

Holotype male: 9.50 mm long, 3.73 mm wide, subdepressed, above submetallic dark coppery brown, below shining metallic black with lateral coppery reflections; head more shining aeneous coppery brown below, black above, coppery brown on vertex; portions of pronotum, particularly near front margin, blackish in certain lights; vestiture white.

Head rather evenly shallowly convex, moderately, densely punctate, with a fine median carina on vertex that ends in a distinct chevron at top of frons, and with a pair of round flattened callosities at middle; setae moderately long, suberect; front margin of clypeus broadly deeply arcuately emarginate; antennae black with brassy reflections, outer portions of segments 4–11 brown. Pronotum shallowly evenly convex, with a vague longitudinal median depression; surface with punctures similar to head, sparser at middle, becoming confused laterally and with rugae developing; front margin broadly arcuately lobed at middle; hind margin evenly bisinuate, truncate in front of scutellum; sides slightly swollen, margins entire, shallowly arcuate, constricted before subquadrate basal angles, front angles narrowly triangular; setae short, sparse, indistinct on disk. Elytra distinctly wider than pronotum, constricted basally, widest back of middle, subparallel to about apical 1/4, then gradually converging to narrowly rounded apices that do not quite cover abdomen; basal margins rather evenly arcuate, lateral margins not serrate; basal depressions distinct, humeral depressions distinct but shallower; each elytron with four weak and variably developed longitudinal costae, three discal and one lateral (the third obsolete on left side) and with a vague brassy marking interrupting the third costa at about apical 1/4; surface rather evenly densely punctate, punctures smaller than on pronotum, finer and sparser apically, setae short and sparse. Underside: prosternum broadly distinctly lobed in front, coarsely densely punctate, with setae long and dense. Abdomen with lateral callosities distinct on sternites 3–4, vaguely developed on sternites 1 and 5, moderately and finely punctate, setae about length of those on head, mostly recumbent; last visible sternite with lateral margins entire, without submarginal ridges, apex with a broad shallow emargination that is limited ventrally by a fine truncate margin; eighth tergite vaguely bluish black, without trace of median carina, distinctly microreticulate, moderately punctured, apex broadly shallowly emarginate. Anterior femur with a large broadly triangular tooth that is not denticulate on outer margin. Anterior tibia slightly arcuate, with a rounded dilation that is strongly constricted just before apex, similar to C. oregona Chamberlin. Genitalia as in Fig. 4 .

Allotype female: 9.96 mm long, 3.88 mm wide, sexually differing from male as follows: head black with only vague metallic reflections, except clypeus coppery; apex of abdomen more exposed; prosternal vestiture much less dense; apex of last visible sternite much more narrowly and shallowly emarginate, with no trace of margin below; eighth tergite narrower apically, greenish black basally, copper apically, more coarsely and densely punctate; anterior tibia almost straight, unmodified apically.

Type specimens: holotype ( CASC No. 18049) labeled “ I80 N, 2.8 mi W Rowena, Wasco Co., ORE., VIII­5­1973, Eriogonum elatum, R. L. Westcott / HOLOTYPE Chrysobothris eriogoni R. L. Westcott ” (red label); allotype ( CASC), Rowena Crest, 6 mi E. Mosier, Wasco Co., Oregon, 26­VII­73, R. L. Westcott, on host plant Eriogonum elatum Dougl. ex Benth. Paratypes: OREGON, 55 males and 39 females, from the same and immediate localities as holotype and allotype, same dates plus 27­VII & 1­VIII­71, 11­ VIII­75, 18­VII­78, 4­VIII­94. Crook Co., 13 mi E Prineville [3,200’], 18­VII, 3 & 4­ VIII­83; 2­VIII­83, reared from host. All specimens are from Eriogonum elatum except six specimens collected 18­VII­78 that are labeled from E. compositum , probably in error. Collectors were F. M. Beer, G. H. Nelson, R. L. Penrose and R. L. Westcott. WASHING­ TON, 1 male, White Swan [Yakima Co.], 4­VII­32, S. E. Crumb, truck crop No. 4973; 2 females, Rimrock [Yakima Co.], 11­VIII­52, H. P. Lanchester; and Wenatchee [Chelan Co.], 28­VI­31. R. W. Kiser. Paratypes deposited in BMNH, CLBC, GHNC, LACM, ODAC, OSAC, RLWE, SGWC, TCMC, USNM, WFBC, WFBM, WSUC.

Variation: In length, males range from 8.10 – 9.96 mm; females from 8.42 – 11.40 mm. Color of dorsum varies from distinctly copper to dark brown with vague copper reflections (some color differences could be an artifact of actual or specimen age). The color of the pronotum varies to being, on occasion, almost entirely blackish, thus contrasting markedly with the elytra; the ventral surface may lack lateral copper reflections. The lateral abdominal callosities are variably developed—sometimes smooth, sometimes punctured—but are always distinct on sternites 2 – 4, rarely evident on sternite 5. The apical margin of the latter in females varies to all degrees between the examples in Figs. (1 – 3). The front of the head in males may have indistinct metallic reflections and/or lack aeneous luster, varying to almost entirely black; conversely, coppery reflections may be distinct and extensive on females. Development of the vertical carina, chevron and median callosities on frons is variable; however, those structures are always distinct. Sometimes the callosities are elongated and coalesced, and the carina may extend beyond the chevron, sometimes ending between the callosities. The median depression on the pronotum may be shortened and indistinct. On the elytra, development of the costae is highly variable, to the degree that on a given specimen one or more may be entirely or partially absent. A few specimens have a distinct second, smaller brassy marking located nearby and mesoapically to the mark described for the holotype. On some specimens one or both of those markings may be indistinct; they may be unicolorous or obsolete.

Distribution: Specimens have been seen only from central Oregon to south central Washington, east of the Cascades and in the Columbia Gorge.

Biology: This species has been collected on dry slopes and flats just east of the Cascade Range only on Eriogonum elatum (Polygonaceae) , a species of wild buckwheat ( Fig. 7 ) that occurs from northern California to Washington, Idaho and Nevada. This plant has a dense woody caudex that is simple or branched (as more commonly observed at collecting sites), a long taproot, and a 30–80 cm long, slightly inflated flowering stem. The plants sometimes grow in large, almost pure stands, particularly in flat areas, probably favored by disturbance. In most places, common associates are Balsamorhiza sagittata , Ceanothus integerrimus , Eriogonum compositum , Quercus garryana, Pinus ponderosa, and Toxicodendron diversilobum . To obtain biological data, plant material was collected 5 & 22 August, 1973; 6 February & 20 June, 1974; 5 & 11 July, 2004, and examined in the laboratory.

During August eggs were found, many of them hatched. Eggs are whitish to yellow, depending upon development of the embryo, measure approximately 1.4 mm X 1.0 mm; dorsal surface slightly convex, thicker, microcrenulatostriate­granulate; ventral surface flattened, thinner, with no apparent sculpturing at 50X magnification. Almost all were found laid inside one to several dead leaf petiole bases, or those of the current year, mostly those surrounding a flowering stalk. Apparently they bear no adhesive and are held in place by plant hairs and/or tight quarters. Many first instar larvae were found associated with their eggs, though some had bored several millimeters into flower stalks or leaf crowns.

Larvae (n=65) from all samples were measured for length, which ranged from 1.5 mm (obvious hatchling) to 18 mm. Only one (15 mm), from the June sample, appeared to be a prepupa. No pupae or live adults were found, although adult exit holes were observed, usually at or near the base of old flower stalks or in leaf crowns. However, some remains were found even in the upper portion of root, perhaps indicating that successful emergence depends upon more ready access to the outside world. Clearly, at least two size classes of larvae were found on each date. Unfortunately, measurement of a sclerotized structure (the epistoma) was made for only the 2004 larvae (n=13). Those were grouped as follows (with number and larval lengths in parentheses): 0.57 mm (1, 8.4 mm), 0.72–0.84 mm (10, 8.4– 4.14 mm), 1.05–1.08 mm (2, 15.4 – 15.6 mm). Larvae start boring into the base of current year flower stalks or leaf crowns, eventually finding their way into the caudex and, less commonly, the roots. There they are in competition with Synanthedon polygoni (H. Edwards) ( Lepidoptera : Sesiidae ); however, competition seems tempered because in the root it was much more common to encounter boring by moth larvae, while C. eriogoni appeared significantly more common in the caudex and crown areas ( Fig. 6 ). Interestingly, Kallies (1997) reported larvae of Synanthedon formicaeformis (Esper) preying on the larvae of the buprestid beetle, Ovalisia dives (Guillebeau) in willow, though Bílý (2002) suggested this is an example of food competition rather than true predation.

Surely the life cycle for this beetle takes at least two years. The evidence for a third year is incomplete, yet the presence of a few large larvae late in the season, during or after adult emergence, and smaller (5–9 mm) larvae during June, 1974, argues for it. In Oregon, adults have been collected from 18 July to 11 August, most commonly during the last week of July and the first week of August. Of 82 specimens collected at and near the type locality (ca. 125’–600’ elevation), 65 were taken from 26 July to 1 August. It is interesting to note that, in 1973, 18 specimens were collected on 26 July and six on 5 August, but none were found during a 30­minute search on 22 August. Of further interest is that only seven specimens were collected during even numbered years, those being at the type locality or very nearby by two very thorough and focused collectors, F. M. Beer and G. H. Nelson. This could simply be a collecting artifact; it could also indicate that C. eriogoni is much more abundant during odd numbered years, an argument for the two­year life cycle.

Comparisons: Chrysobothris eriogoni keys to C. oregona Chamberlin in Fisher (1942), and clearly it is most closely related to that species. Both belong to a group of species that appears to be in a high state of evolutionary plasticity, the known hosts of which mostly fall within the families Asteraceae , Polygonaceae and Rosaceae . Most of the species are poorly defined, sharing overlapping characters and being highly variable. Even the aedeagus can show variability, to the point that it may not be the uniformly reliable diagnostic character so common in the genus. In Polygonaceae , species of Eriogonum host a wide variety of these beetles, though not all of them have been associated by rearing. An example is C. oregona , though the vast majority of specimens have been collected on plants in other families, notably Rosaceae . Perhaps C. eriogoni evolved from C. oregona via a recent hostplant shift.

Host plant aside, the most reliable way to separate the two species is as follows: in C. eriogoni , the elytral costae are less prominent and unicolorous with the elytra, and the elytral foveae are absent or weak except sometimes apically (usually only on one side), while in C. oregona all four costae are usually prominent and dark, in contrast to the elytral ground color. In males of C. oregona the front of the head is almost always distinctly green, while in C. eriogoni it is coppery brown to black. In series, it can be noted that C. eriogoni is larger, though possibly this is due to association with a larger host. Length was measured on 25 specimens of each species: C. eriogoni ranged from 8.23 mm to 11.31 mm (see also under “Variation”), averaging 9.69 mm; C. oregona ranged from 5.27 mm to 9.26 mm, averaging 7.27 mm.

Chrysobothris eriogoni is also quite closely related to C. fragariae Fisher , but that species differs primarily by usually being darker in color and with the elytral costae fewer in number, obsolete or weakly defined. Interestingly, it or a very closely related species occurs with C. eriogoni at and near the type locality of the latter in a related host, Eriogonum compositum , with the adults being active about a month earlier. It appears that Fisher’s (1942) treatment of C. fragariae may have included specimens of all three of the species being compared here. A paratype of C. eriogoni from White Swan, Washington, was one of them.

Figures

FIGURE 7. Habitat at type locality of Chrysobothris eriogoni sp. nov. showing host plant, Eriogonum elatum.

FIGURES 1 – 6, Chrysobothris eriogoni, sp. nov.: Figs. 1 – 3, apex of last visible sternite, female; Fig. 4, aedeagus; Fig. 5, adult male, paratype; Fig. 6, late instar larva in crown of host plant, Eriogonum elatum.