Antibothrus morimotoi Sasaji 1997

Mcelrath, Thomas C., Androw, Robert A. & Mchugh, Joseph V., 2016, Antibothrus morimotoi Sasaji, an Old World cocoon-forming beetle (Coleoptera: Coccinelloidea: Bothrideridae) newly established in North America, Zootaxa 4154 (3), pp. 323-330 : 325-328

Antibothrus morimotoi Sasaji 1997

( Figure 1 )

Species diagnosis. In the New World, A. morimotoi is the only species of Antibothrus currently established. Thus, the generic level diagnostic characters are sufficient to distinguish it from all other species of Bothrideridae that are known to occur in North America.

When compared with similar species of Antibothrus in its native range, A. morimotoi can be distinguished by the peculiar form of the basal two antennal segments (scape with stout spine protruding asymmetrically; pedicel wider than following segment, inserted asymmetrically into scape); penultimate antennal segment much wider than terminal segment [of similar width in A. fatalis ( Nikitsky 1985a) ]; eyes prominent laterally; pronotal longitudinal furrow barely impressed; lateral edges of pronotum rounded, not carinate; sub-interval carinae of elytra shorter; and short stout setae on apex of elytra lacking [present in A. hirsutus Aoki (Aoki 2009) ].

Species redescription (modified from Sasaji 1997, additional terminology from Lawrence et al. 2010)

Body: somewhat cylindrical-flat, about 3.1× as long as wide, nearly parallel-sided. Uniformly reddish brown or yellowish brown, without any dark or light markings. Surface almost glabrous.

Head: Relatively large, wider than long in dorsal aspect. Eyes strongly prominent laterally and glabrous. Frons finely and sparsely punctate. Fronto-clypeal suture distinct. Clypeus wider than long, with visible setae near apex. Antenna clearly 11-segmented. Scape (A1) stout, mostly glabrous with small setal fringe preceding A2 insertion, with acute subbasal spine on outer edge, spine with associated longer seta; pedicel (A2) much smaller than A1 but strongly widened (measured perpendicularly to A1 insertion), inserted asymmetrically on A1 outer lateral edge; A3 subcylindrical, slightly longer than wide; A4–9 each wider than long; A10 strongly widening apically, about twice as wide as long; terminal antennomere (A11) transverse oval, much wider than long, with narrow stem, about 2/3 size of A10. Genal processes expanded into acute points ventrally.

Prothorax: Nearly as long as wide, hexagonal, with weakly angulate sides. Surface of pronotal disc roughly sculptured by large (0.1–0.2 mm), irregular, elongate-oval punctures, each with a single minute, short seta. Pronotal base with a pair of weak and very short admedian elevations bordered laterally by weak depressions and mesally with an additional weak median depression. Lateral pronotal carina weakly present basally, nearly obliterated anteriorly. Prosternal process very narrow, and weakly widening posteriorly with a subtruncate apex, and nearly as long as basisternal length. Postcoxal process of prothoracic hypomeron very narrow.

Pterothorax: Scutellar shield small, wider than long. Mesocoxal cavities closed externally, separated by ~1/2 width of mesocoxal cavity, subcircular. Mesoventrite trapezoidal, roughly punctured, nearly as long as mesocoxal cavity (not including mesoventral process); mesoventral process with gradual elevation anteromedially, reaching level of metaventrite; mesanepisternum distinctly separated from mesoventrite, roughly punctured, subtriangular in lateral view. Meso-metaventral junction straight. Metaventrite longer than first abdominal ventrite, coarsely and more densely punctured, with some minute setation. Metanepisternum long, thin, not expanded, impunctate.

Elytra: Anteriorly wider than prothorax, widest in anterior third; almost parallel-sided with a short rounded apex. Disc of elytron with three distinct longitudinal carinae, reaching almost to elytral apex; suture also carinate; each of three intervals with a weak longitudinal carina at anterior half or anterior two-thirds. Surface of interstices between carinae very weakly, sparsely punctate, mostly smooth; nearly glabrous, except for minute, sparse setae only visible under high magnification.

Abdomen: Intercoxal process broad, flat, truncate. Ventrite one (V1) longest, about 2–3× as long as each of the remaining ventrites (V2–5). All ventrites somewhat coarsely, densely punctured. V1 mostly flat, curving towards dorsum laterally. V2-4 subequal in length. V2–4 each with median posterior margin with ridge-like expansion away from body, especially V4, so that the posterior edges of V2–4 project more strongly ventrad than the anterior edges. V5 mostly flattened, slightly longer than V4.

Legs: Tarsal formula 4-4-4, basal and terminal tarsomeres longest. Tibial spur formula 1-2-2. Protibia with sharp terminal outward extension forming spine and several small but distinct denticles along outer edge; protibia with one long (nearly reaching apex of first tarsomere), slender, socketed, darkened, apically curved tibial spur. Meso- and metatibia each with a sharp terminal outward extension forming spine and two subequal, straight tibial spurs, each shorter and less robust than protibial spur.

Body length: 2.00– 2.35 mm (avg. 2.17 mm) (up to 2.5 mm in native range); width: 0.65–0.75 mm (avg. 0.69 mm) (n = 20, all specimens included).

Distribution. JAPAN (Honshu: Fukui, Mie, Nara and Hyôgo); UNITED STATES (Ohio: Franklin Co.) ( Fig. 2 ).

Biology. Antibothrus fatalis is associated with burrows of the scolytine genus Xyleborus ( Nikitsky 1985a) . Two species of Antibothrus have been collected beneath the bark of trees: Antibothrus ichihashii on Castanopsis sieboldii ( Narukawa 2002) and A. hirsutus on an unidentified tree. The specimens of A. morimotoi found in North America were all collected by Lindgren funnel traps baited with various bark beetle attractants, such as alphapinene, Platypus quercivorus or Megaplatypus lure, and ethanol. Considering that most members of Bothrideridae are ectoparasites of wood-boring insect larvae, the capture of A. morimotoi in these baited traps suggests that the species is ectoparasitic on larvae of bark beetles, perhaps a species of Xyleborus .

Interestingly, the specimens collected in 2013 were slightly shorter (x̄= 2.14 mm, n = 15) than those collected in 2015 (x̄= 2.27 mm, n = 5). While this difference is not statistically significant, it was readily visible and easily measurable. This may be due to changes in the host species utilized, or the health (and nutritional value) of the host species between the two years, or alternatively, to the number of individuals utilizing a single host larva or pupa.

Figures

FIGURE 1. Antibothrus morimotoi (a) dorsal, (b) ventral, and (c) lateral habitus. Images by TC McElrath.

FIGURE 2. Map of Antibothrus morimotoi specimen collecting events reported in this work. Yellow and red pins are 2013 and 2015 collection points, respectively. Image created with GoogleEarth ™ version 7.1. 5.1557. Interactive KML file available: “ https: // archive. org / download / Antibothrus / Antibothrus. kml ”