New species and records of Cactopinus Schwarz with a key to species (Coleoptera, Curculionidae, Scolytinae)

Abstract Three new species in the genus Cactopinus Schwarz are described from Mexico and the U.S., bringing the total of known species to 21. New host and distribution records and a new key to species are included.

Th e most noteworthy character of the genus is the presence of paired horns on the male epistomal process. In all species the 2 horns are apparently distinct from their base to their apex. In some species the horns are short and widely separated (Figs 2,5). Otherwise the horns are fused at their bases and for most of their length, even though there is a clear suture between them (Figs 29,33). In some species horns extend from the epistoma to the middle of the pronotum. In these species the horns apparently maintain some fl exibility, based on the variation in position in preserved specimens. In some specimens the horn is straight (Fig. 23) while in others it is curved backwards over the frons and pronotum (Fig. 27). While the horns are not segmented, they have setae set into deep punctures along their length which might allow some fl exibility. In some species the punctures are so pronounced that the horns have a serrate appearance (Fig. 33). Th e apex of the horns is parallel in some species (Fig. 12) or strongly divergent in others (Fig. 15) and may appear digitate (Figs 24,28,33). In addition to marked diff erences in horn length among species, the length of horns is strongly variable within species as well. In females of some species, indistinct, raised calluses are present in positions similar to the location of the base of the horns in males (Fig. 30). In addition to the primary epistomal horns, usually located in the center of the epistomal process, a short tubercle or projection is found on the anterolateral margins of epistoma near the base of the antennal insertion in most species (Fig. 2,8,17,24). In C. spinatus Wood (Fig. 35) there is a distinct spine between the primary horns and this outer spine or projection.
Along with the development of the epistomal horns there has been a parallel anteroventral elongation of the head, particularly in males. Th is is evident even in species with relatively short horns (Figs 1, 10). Th e compound eyes have also been moved forwards and ventrally and are foreshortened by comparison with other scolytines. Th e male frons is generally concave from vertex to base of horns in lateral view. In some species, despite this longitudinal curvature, the resulting surface between the eyes is essentially fl at (e.g., cactophthorus Wood,Fig. 11,12). In most species, however, the frons is longitudinally concave as well with a well defi ned fossa that varies in extent (Figs 8,17,19). In most females the frons is fl at or convex, often transversely impressed immediately above the epistoma. Th e size and shape of the antennal club varies among species in size relative to the size of the head and shape (rounded or oval). Antennal sutures vary from mostly straight to procurved, or weakly bisinuate.
In most groups of the Scolytinae (sensu Wood 1982) asperities are found between the anterior margin and the center of the pronotum, generally with a distinct summit near the middle. In Cactopinus, this summit is invariably on the posterior margin of the pronotum and in some cases is developed into a cone that strongly projects backwards. In some species the pronotal asperities are clearly arranged in a triangular pattern with the asperities broadly distributed near the anterior margin, tapering sharply to the summit (Figs 23,25,27,29). In these species there is a sharp demarcation between the asperate areas and the non-asperate posterolateral area. In most species, asperities are also found on the posterolateral portions of the pronotum (Figs 3, 6, 13).
Many specimens in collections are covered with a crust of plant resins and boring dust. Th is can be cleaned off by soaking in acetone or ethyl acetate overnight, combined with gentle ultrasonic cleaning. Once cleaned the elytral surface of all species is shining. At the same time, the interstrial surface of the disc is generally irregular. Strial punctures (and sometimes interstrial punctures) are usually deep, although the striae themselves are generally not impressed. Granules are frequently associated with interstriae on the declivity (Figs 4,7,9), to the base of elytra in some cases (Fig. 3). In some species granules are associated with striae as well. Th e declivity of all species is steep in lateral view, ranging from nearly convex to deeply sulcate. Lateral elevations (usually interstriae 2-4) sometimes do not extend to the costal margin and extend beyond the apex of elytra in lateral view (Figs 1, 7), appearing as lobes. Th e apex of the declivity is normally truncate in dorsal view but weakly acuminate in some cases (Figs 26,39).
While each species is host specifi c, generally at the genus level, collectively they are found in a variety of totally unrelated hosts. Hosts include pines (2 species), Bursera spp. (Burseraceae, 2 species), Rhus spp. (Anacardiaceae, 1 species), leaves of the Agavaceae (Yucca spp., 1 species; Agave spp., 1 species), and various genera and species of columnar cacti (14 species). Actual hosts of at least half of the species breeding in cacti are not known. Th e only thing that the diff erent hosts have in common appears to be co-occurrence in arid plant communities. All species have the ability to breed in apparently completely dry host material. Partly as a consequence, it is typical to see signs of breeding by multiple generations within the same piece of host material. Th is appears to be an adaptation to the xeric habitats where these hosts occur. While this is unusual with the Scolytinae, similar behavior is found in other groups, notably the Micracina. Based on a subjective analysis of morphological characteristics, it would appear that columnar cacti are probably the ancestral hosts and that other hosts associations are derived (widely separated vs. basally fused epistomal horns; shorter vs. longer horns; weakly developed pronotal asperities and poorly developed summit vs. strongly pronounced asperities with posteriorly projecting summit).
All species, so far as is known, are monogynous, with galleries constructed by a single pair. Which sex initiates galleries is unknown. In cases where multiple generations breed in the same piece of host material it is not known whether beetles emerge upon maturity and re-enter host tissues or whether new galleries are initiated without emerging. Galleries of several species have been described by Wood (1957) and Bright (1967) as an irregular, elongate gallery, several times wider than the width of adults, frequently fi lled with frass, and with multiple larval mines proceeding from poorly defi ned egg niches. I have seen similar galleries in C. agavensis and C. depressus. In most cactus-breeding species it is diffi cult to interpret adult galleries. In several of those species I have observed that galleries are initiated in the areoles (clusters of spines) along the outer ridge of the ribs. Galleries are then excavated under the tough epidermis and eggs appear to be deposited in individual niches.

Systematics
Cactopinus woodi Atkinson, sp. n. urn:lsid:zoobank.org:act:0911530D-453A-4628-9AC8-380095EB422B Figs 1-4 Description. Th is species is named in honor of Steve Wood, especially appropriate considering the large number of species in this genus that he described. It is easily recognized by its widely separated, short epistomal horns and by the large, uniform granules associated with all interstrial and strial punctures on the disc to its base and on the declivity, except for striae and interstriae 1 and 2.
Male. Color black. Length 1.4-1.6 mm, width 0.6-0.7 mm, length/width 2.3. Epistomal horns short, length 2-3× basal diameter, widely separated by distance greater than length; without any associated setae. Frons weakly concave from epistoma to upper level of eyes; concavity without raised margin dorsally or laterally; surface of concavity smooth, impunctate; setae sparse, short, most abundant on periphery of concavity. Antenna subcircular, sutures slightly procurved. Pronotum with asperities concentrated near middle; summit at posterior margin, not strongly pronounced; some asperities on postero-lateral areas; area of greatest concentration of asperities not sharply demarcated laterally. Striae deeply punctured; all punctures associated with rounded granules to base of elytra; granules occupying entire space between adjacent punctures. Interstriae 1.5× as wide as striae; setae uniseriate, each associated with a rounded granule to base. Granules on striae and interstriae similar in size. Declivity steep, rounded posteriorly, strongly sulcate. Striae 1 and 2 impressed; granules absent; punctures smaller than on disc; granules also absent from associated interstriae. Interstriae 3 narrowly elevated, forming a distinct crest; its granules larger than on disc. All other declivital striae and interstriae similar to those of disc. Lateral elevations highest in middle, projecting beyond apex of elytra in lateral view.
Female. Frons fl attened, surface sparsely punctured, setose in central area. Other characters identical to those of males. Notes. Th is species has been collected in the dried ribs of its host cacti. As is the case with most other cactus-breeding species, successful breeding occurs in portions of stems that have dried out to a hard, yellowish color, without the black discoloration associated with decay. Th is situation most commonly occurs in erect, dead stems still attached to the host. In pieces that fall to the ground the upper surface is apparently too hot from direct exposure to the sun and the lower surface seems likely to decay from contact with the soil. Galleries are initiated at the areoles, clumps of spines that are found along the ridges of the ribs. Description. Th is species is readily distinguished from other species with short, separated epistomal horns by the nearly fl at male frons with only a narrow, longitudinal sulcus. Th is frontal sulcus is the basis for the specifi c epithet.

Cactopinus sulcifrons
Male. Color black. Length 1.4-1.7 mm, width 0.6-0.7 mm; length / width 2.4. Epistomal horns short, pointed, height slightly greater than basal diameter; located near center of epistoma, separated by 1.5× height. Frons fl attened with narrow longitudinal sulcus in center, not wider than the distance between the horns. Surface  sparsely punctured, with short setae; setae and punctures more abundant on periphery. Asperities on anterior margin tooth like, widely separated, becoming more abundant, fl atter, and densely packed towards center and summit. Asperities are tightly packed, and slightly overlapping in a triangular pattern in the center and posterior of the pronotum, but less densely spaced asperities are abundant in posterolateral areas to the posterior margin. Striae not impressed, punctures deep, spaced within row by distance equal to their own diameters. Interstriae 1.5× as wide as striae with shallow uniseriate punctures. Vestiture of short strial setae and longer, erect interstrial setae, becoming longer posteriorly. Declivity steep, sulcate, with lateral elevations strongly elevated in middle, posterior margin rounded. All interstriae except 1-2 with rounded, uniseriate granules beginning at base of declivity. Punctures on striae 1 and 2 smaller than on disc. Lateral elevations very wide, consisting of elevated portions of interstriae 3-5.
Female. Frons transversely impressed above epistoma, convex above, surface sparsely punctured, setose in central area. Epistoma with low calluses in same position as male horns. Other characters identical to those of males. Notes. Th e habits of C. sulcifrons are similar to those of C. woodi. elongate, 1.7 times longer than wide, sutures straight. Pronotum with asperities widely separated at anterior margin, most abundant in center; arranged in sharply defi ned triangular pattern with no asperities or granules in posterolateral portions. Clearly defi ned summit at posterior margin, strongly elevated into a point, projecting backwards over elytra. Striae not impressed, with deep punctures, separated by less than their own diameter. Interstriae not elevated, about twice as wide as striae; surface irregular, with numerous, fi ne, confused punctures. Vestiture of recumbent, short, strial setae, with long, ribbon-like interstrial setae, these longer than distance between rows. Declivity weakly sulcate, gradual, slightly acuminate posteriorly. Interstriae 1 and 2 wider on declivity than on disc. Punctures on striae 1 absent beyond declivital base, interstriae 1 and 2 with numerous, small, confused punctures. Interstrial granules on all other declivital interstriae except 1. Interstriae 2 strongly elevated, its granules slightly longer and sharper than those on other interstriae.

Cactopinus agavensis
Female. 2 wide calluses present on epistoma, frons transversely impressed above. Frons shallowly concave above transverse impression, surface with shallow, large, closely set punctures. A fringe of setae along upper and lateral margins of convavity. Other characters identical to those of males. Notes. Th is species has been collected on 3 occasions in the central Mexican highlands from the large semi-domesticated agaves used historically for pulque production. Th ese plants reach a very large size with individual leaves reaching a length of 1.5 m or more and armed with strong, recurved spines. Th e insect is found in dead, mostly dry leaves at the bottom of the rosette. In a healthy plant, the only way to get to these leaves is to basically take the plant apart, something that requires a lot of work and potential loss of blood on the part of would-be collectors. It is more easily collected from rosettes that are dying and beginning to fall apart after blooming, or in the occasional specimen growing on the edge of a terrace or wall such that the lower leaves can be reached. Th e beetles may enter the leaves from either the top or bottom surface and galleries resemble those described by Wood (1982). Apparently multiple generations may develop in the same dried leaf until it is consumed.

Key to males of Cactopinus
Information on hosts and distribution is included in the key as a general aid to users. Distributional information should only be used in a very general sense given that many species are still known only from type localities.

1
Asperities on pronotum large, chisel-like, forming distinct triangle with apex at posterior margin, clear demarcation between this area and posterolateral portions of pronotum, most asperities posterior to middle (Figs 23,25,27,29); antennal club narrow, 1.7-2 times as long as wide, sutures straight (Fig. 33) Asperities on pronotum small, often granulate, more evenly distributed, not in clearly marked triangular pattern, apex indistinct or not strongly projecting backwards; most asperities anterior to middle (Figs 3, 6, 13); antennal club rounded, less than 1.3 times as long as wide, sutures weakly procurved to bisinuate (Fig. 21) Epistomal horns about twice as long as basal diameter, separated by more than twice their length; frons shallowly concave; prominent granules on all declivital striae and interstriae to base. 1.4-1.6 mm. In Stenocereus spp. Arizona, Baja California, Sonora (Figs 1-4)  Upper part of concavity of frons wider above eyes, upper margin acute; declivity more pronounced, interstriae 2 narrowed, without granules except near base ...10 -Upper part of frontal concavity not wider above eyes, upper margin less pronounced; declivity shallower, interstriae 2 not narrowed, with granules for its full length. 1.3-1.5 mm. In Stenocereus spp. Jalisco. (Figs 8-10).....atkinsoni Wood 10(9) Upper half of frons bearing longitudinal carina; apex of pronotal summit not developed into backwards-projecting cone. 1.5-1,8 mm. In Myrtillocactus. Hidalgo, San Luís Potosí, Tamaulipas. (Figs 17, 18)   . Th ese collections represent new state records and the fi rst known host records for this species. M. geometrizans is one of the most widespread of the arborescent-columnar cacti in Mexico and is easily recognizable. It is known to occur in the vicinity of the type locality for C. carinatus. While it is premature to conclude that this species is the only host for C. carinatus, it is signifi cant that it has not been collected in numerous recent collections from other species of cacti.

Cactopinus spinatus Wood
Previously the only known hosts were tropical trees and shrubs of the genus Bursera, although Wood (1982) indicated that he had collected it from hosts that did not appear to be of that genus. Mexico: Oaxaca: Cuicatlán, 5 km N; 17.74010N, 96.94901 W; 665 m; 2-VII-2009; Cyrtocarpa procera (Anacardiaceae), T.H. Atkinson . Th e families Burseraceae and Anacardiaceae are closely related both taxonomically and chemically.