Tragidion armatum LeConte

Swift, Ian & Ray, Ann M., 2008, A review of the genus Tragidion Audinet-Serville, 1834 (Coleoptera: Cerambycidae: Cerambycinae: Trachyderini), Zootaxa 1892, pp. 1-25 : 13-14

Tragidion armatum LeConte

( Figs 1 E–F, 6A)

Tragidion armatum armatum LeConte, 1858:25 ; Lacordaire, 1869:174; LeConte, 1873:314; LeConte and Horn, 1883:299; Leng, 1886:81; Casey, 1893:586; Casey, 1912:324; Linsley, 1942:60; Linsley, 1962:119; Hovore, 1988:28. Type locality: Llano Estacado, New Mexico, Texas.

Tragidion texanum Schaeffer, 1932:152 . Type locality: Texas.

Tragidion armatum brevipenne Linsley, 1957:33 ; Linsley, 1962:119; Hovore, 1988:28. Type locality: Daggett, San Bernardino County, California. New synonymy.

Material examined: 118 specimens, including the holotypes of T. armatum at MCZC and T. a. brevipenne at CASC.

Diagnosis. Tragidion armatum is most similar T. agave and T. gracilipes . See both species accounts for diagnoses.

Populations of T. armatum exhibit some morphological variation throughout the geographical range of the species. Populations from cismontane California tend to have smaller antennae-to-body ratios and are smaller in overall size. Material from New Mexico and Texas tend to be somewhat lighter colored.

The characters separating T. a. brevipenne from the nominate subspecies are highly variable ( Linsley 1957). The short elytral character is not consistent among series, even from topotypic material, and seems largely to depend upon how a given specimen was mounted.

Distribution ( Fig. 6 A). This species occurs commonly throughout the southwestern United States including California, Arizona, Nevada, Utah, New Mexico, and Texas and the northern states of Mexico, including Baja California, Sonora, and Chihuahua. It is found in a variety of desert habitats in the southwest, as well as chaparral, coastal sage scrub, and oak woodland in cismontane California.

Ecology. Tragidion armatum utilizes host plants in the family Agavaceae , in the genera Yucca and Agave , including: Y. brevifolia , Y. elata , Y. baccata (new host record), Y. schidigera , and Y. (= Hesperoyucca ) whipplei, Agave deserti, A. palmeri (new host record) ( Waring and Smith 1987). Chemsak and Powell (1966) provide an excellent summary of behavior, distribution, physiology, and host plant preferences. Larvae can take as long as four years to develop in very xeric habitats, and flower stalks of Y. brevifolia frequently contain multiple generations of larvae. During several cycles of drought years in the western Mohave Desert, adults did not emerge, and larvae may enter dormancy during these periods.

Populations from cismontane California occur in chaparral and oak woodland, an atypical habitat when contrasted with the desert habitats from the remainder of their range. They also occur in widely scattered populations, being absent from large expanses of otherwise suitable habitat containing large numbers of host plants. Within this region, T. armatum is entirely obligate upon Hesperoyucca whipplei . This host can require seven or more years to produce a floral stalk, which is the food source for the larvae. Hesperoyucca whipplei has populations exhibiting different reproductive strategies including semelparism, iteroparism, and clonalism ( Keeley, et al. 1986). The former, reproducing from seed after the mature parent has died, the latter two generally producing flowering stalks each year (i.e. larval host). Given the long interval between germination and flower stalk production in semelparous plants, suitable host material may not be widely available for prolonged periods of time. Based on specimen distributional data and field observations, T. armatum only occurs in association with non-semelparous host plants and is absent from areas of semelparous hosts.

Figures

FIGURE 1. Dorsal habitus photos of Tragidion spp. A, Tragidion agave (male); B, T. agave (female); C, T. annulatum (male); D, T. annulatum (female); E, T. armatum (male); F, T. armatum (female).

FIGURE 6. Distribution map of Tragidion spp. A, Tragidion armatum; B, T. bicolor; C, T. carinatum; D, T. coquus; E, T. dichromaticum.