Cactopinus rhettbutleri Atkinson

Atkinson, Thomas H., 2016, A new species of Cactopinus Schwarz from central Mexico (Coleoptera: Curculionidae: Scolytinae), Zootaxa 4189 (1), pp. 196-200 : 196-200

Cactopinus rhettbutleri Atkinson , sp. n.

Male: ( Figs. 1–2 ). Color black, length 1.87 mm (1.8–2.05), width 0.85 mm (0.8–1.0), length/width 2.19 (1.9–2.4) (n=11).

Head: Dense fringe of downwards projecting, fimbriate setae along entire width of epistomal margin, covering base of mandibles; similar, smaller brushes at base of mandibles at genal margin. Epistoma raised for its entire width, with a single, small tubercle at each end, rising gradually in middle to base of horns. Horns joined at base, parallel throughout their length along interior margins, broadened distally; anterior surface shining, deeply, coarsely punctured, with yellowish setae arising from punctures; apex of horns digitate, impunctate; punctures on external margins of horns with raised lateral elevations; the most distal of these with a prominent lateral process, giving the horn a forked appearance; a large brush of yellow setae arising from this cleft, length of setae exceeding the apex, similar in size and color to those of epistomal brush. Frons concave in profile, shallowly concave in medial area between eyes, margins of concavity gradual, not acute; frontal surface above horns coarsely punctured, largely without setae; surface shining. Antennal club approximately twice as long as wide; basal half corneous, 2 straight sutures evident on distal half, lined with yellow setae.

Pronotum: Asperities concentrated behind middle; summit acute, slightly projected posteriorly beyond base; asperities on anterior slope sparse, separated, tooth-like. Postero-lateral portions of pronotum smooth, shining, with widely spaced, deep punctures; this area with a clear demarcation from densely placed, confused asperities on summit. Acute setae associated with punctures throughout; those in antero-lateral areas and along lateral margins of raised summit twice as long as others, as long as antennal scape.

Elytra: Striae deeply punctured but not impressed, punctures separated by less than their diameter. Interstriae twice as wide as striae with clearly marked, uniseriate punctures that are smaller than those of the striae; surface smooth and shining; vestiture of erect golden interstrial setae, their length less than that of the interstrial width. Declivity steep; striae 1 impressed with sutural interstria elevated, interstria 2 slightly widened with a small number of widely spaced granules; interstria 3 elevated, highest in middle, but not higher than the sutural interstria; all declivital interstriae (reduced in 2) with small uniseriate granules associated with interstrial punctures; strial punctures not granulate.

Female: ( Fig. 3 ). Length 1.90 mm (1.8–2.05), width 0.86 mm (0.9–0.95), length/width 2.13 (2.1–2.3) (n=11). Frons weakly concave between eyes; surface densely pubescent with setae uniform in length throughout, about 2/3 length of antennal scape, becoming shorter at vertex; brush of marginal setae along epistoma similar to that of male; epistoma without any trace of lateral elevation. Pronotum and elytra similar to that of male.

Type material. Holotype: male. Oaxaca, 7 km S Totolapan, road to Santa María Zoquitlán (16.6231 N; 96.3261 W), 982 m, 24-VII-2014, Polaskia sp., T.H. Atkinson & A. Burgos S., THA-1064 (Deposited in the Coleccion Nacional de Insectos ( CNIN), Instituto de Biología, Universidad Nacional Autónoma de México).

Allotype: female: same data (CNIN).

Paratypes: Oaxaca: 7 km S Totolapan, road to Santa María Zoquitlán (16.6231 N; 96.3261 W), 982 m, 24-VII- 2014, Polaskia sp., T.H. Atkinson & A. Burgos S., THA-1064 ( UTIC, 6) ; 2 km N Totolapan (16.68644 N; 96.32061 W), 1,004 m, 1-VII-2009, Escontria chiotilla, T.H. Atkinson , THA-893 ( TAMU, 2; UTIC, 3) ; 5 km S Totolapan, road to Santa María Zoquitlán (16.6515 N; 96.3156 W), 700 m , 24-VII-2014, Polaskia sp., T.H. Atkinson & A. Burgos S., THA-1060 ( TAMU, 2); Santiago Dominguillo (17.6337 N; 96.9141 W), 870 m , 2-VII- 2009, Escontria chiotilla, T.H. Atkinson , THA-896 ( UTIC, 3); Nejapa (16.6096 N; 96.0134 W), 659 m , 23-VIII- 2014, T.H. Atkinson & A. Burgos S., THA-1058 ( CEAM, 5). Puebla: Coxcatlán (18.2446 N; 97.156 W), 1070 m ; 19-I-2012, Escontria chiotilla ; T.H. Atkinson, THA-979 (CNIN, 2; CEAM, 2; TAMU, 7; UTIC, 6).

Notes. As previously discussed ( Atkinson, 2010) the male epistomal horns are not segmented. In most species, especially those with the longest horns, there are deep punctures along most of the length of the horn that appear to confer some flexibility by allowing it to bend. In C. rhettbutleri the margins of the subapical punctures are raised into projections. This may be seen in several punctures but is always most prominent in those closest to the apex of the horns.

In some males from the Coxcatlán population the epistomal horns are much reduced in size ( Fig. 2 B,C,D). In intermediate cases the distal digitate extension is absent or much reduced but the margins of the subapical punctures are still expanded laterally and the more distal punctures on the lateral margins still have a lateral process arising from them and show the bifid, or forked apex. In other species of Cactopinus for which large numbers of specimens from multiple collections are available, there appears to be considerable variation in the length of male horns. This needs to be studied and possibly descriptions and keys will have to be modified.

Biology. This species has been collected in the dried ribs of its hosts, multiply branched arborescent cacti. As is the case with most other cactus-breeding Cactopinus species, successful breeding occurs in portions of stems that have dried out to a hard, leathery consistency without the black discoloration associated with decay. Under these conditions the dried tissue is dark yellowish brown and tacky to the touch. This situation most commonly occurs in erect, dead stems still attached to the host. Galleries are initiated at the areoles (clumps of spines that are found along the ridges of the ribs). Species of Polaskia are restricted to the states of Oaxaca and Puebla, roughly within the area where this species was collected. Escontria chiotilla has a broader distribution which includes the Balsas depression of the states of Guerrero and Michoacán.

The majority of the species of Cactopinus that breed in columnar or arborescent cacti use hosts in the subtribe Stenocereinae (Gibson et al. 1986). Other reported hosts in this subtribe include Stenocereus and Myrtillocactus . The Escontria and Polaskia also belong to this group and are most closely related to Myrtillocactus .

Etymology. This species is named in honor of Rhett Butler for his work in conservation and environmental education.

Diagnosis. This species is most readily distinguished by the unique, laterally expanded epistomal horns in the male that appear to be apically forked. The wide variation in horn length documented here for C. rhettbutleri means that some specimens can not be reliably identified at this point. The subapical branching that is typical of this species is visible even in males with reduced horns ( Fig. 2 B,C) but not in extreme cases ( Fig. 2 D).

Examination of long series of other species has also shown wide intraspecific variation in male horn length (unpublished) that effectively means that single male specimens of other species may also present problems in identification. At this point females cannot be reliably identified although this could be accomplished with further study. Based on the abundance of characters present in the known species it should be possible to write new keys that will accommodate both females and males with reduced horns. This is beyond the scope of the current paper.

Cactopinus rhettbutleri will key out to couplet 11 in the latest generic key ( Atkinson, 2010). Modified couplets are shown below.

11(8) Frons curved in lateral profile, but flat longitudinally; pronotal asperities blunt, weakly developed; declivity with relatively few, small granules on interstriae. 1.2–1.4 mm. Puebla ......................................... cactophthorus Wood - Frons weakly to prominently concave in central area between eyes; pronotal asperities sharply elevated, chisel shaped declivity with prominent granules on interstriae 2 and higher.......................................................... 12 12(11) Horns reaching or exceeding upper level of frons, apical portions digitate; interstria 1 on declivity not impressed, interstriae 3 not prominently elevated............................................................................... 13 - Horns not reaching upper level of frons, apical portion not digitate, interstria 1 on declivity strongly impressed, interstriae 3 prominently elevated................................................................................. 13a 13(12) Male horns not expanded distally, digitate apical portions of horns divaricate; 1.5–1.6 mm. In Neobuxbaumia . Morelos, Puebla .......................................................................................... burjosi Wood - Male horns expanded distally, prominent lateral process below digitate apex giving forked appearance. In Escontria , Polaskia . Oaxaca, Puebla ....................................................................... rhettbutleri Atkinson 13(13a)Frons with prominent concavity in middle of frons; outer sides of horns parallel, inner sides angled making obvious “V” shape; antennal sutures straight. 1.6–1.9 mm. In Stenocereus . Oaxaca, Querétaro ................................ niger Wood - Frons shallowly concave, concavity not well defined; inner sides of horns not strongly angled; antennal sutures bisinuate. 1.4– 1.7 mm. In Stenocereus spp. Jalisco ............................................................. setosus Wood

Figures

FIGURE 1. Cactopinus rhettbutleri, n. sp. male holotype. A. Dorsal view; B. Lateral view; C. frontal view with epistomal horns; D. Declivity.

FIGURE 2. Cactopinus rhettbutleri, n. sp. Variations in male epistomal horns.

FIGURE 3. Cactopinus rhettbutleri, n. sp. Female paratype. A. Dorsal view; B. Lateral view; C. frontal view; D. Declivity.