Anelaphus villosus

Anelaphus villosus (Fabricius)

(Fig. 2k, 8 a-c, 9a-c)

Stenocorus villosus Fabricius 1792: 302.

Callidium pulverulentum Olivier 1795: (70) 69. Synonymy with E. parallelum by Gahan (1895: 105).

Stenocorus putator Peck 1819: 307.

Elaphidion parallelum Newman 1840: 29, new synonym (Fig. 8b).

Elaphidion arctum Newman 1840: 29. Synonymy with E. parallelum by Horn (1885: 5).

Elaphidion pruinosum Guérin-Ménéville 1844: 225. Synonymy with E. parallelum by LeConte (1873: 183).

Elaphidion rusticum LeConte 1850: 14, new synonym

Elaphidion oblitum LeConte 1850: 14. Synonymy with E. parallelum by LeConte (1873: 183).

Hypermallus abruptus Casey 1912: 301. Synonymy with S. villosus by Linsley (1963: 91).

Hypermallus scuticularis Casey 1912: 302. Synonymy with S. villosus by Linsley (1963: 91).

Hypermallus lacustris Casey 1912: 302. Synonymy with S. villosus by Linsley (1963: 91).

Hypermallus medialis Casey 1912: 302. Synonymy with E. parallelum by Linsley (1963: 92).

Hypermallus medialis canadensis Casey 1912: 303. Synonymy with E. parallelum by Linsley (1963: 92).

Hypermallus medialis densicollis Casey 1912: 303. Synonymy with E. parallelum by Linsley (1963: 92).

Hypermallus defectus Casey 1912: 303. Synonymy with E. parallelum by Linsley (1963: 92).

Hypermallus molliculus Casey 1912: 304. Synonymy with E. parallelum by Linsley (1963: 92).

Hypermallus breviusculus Casey 1914: 364. Synonymy with S. villosus by Linsley (1963: 91).

Hypermallus militaris Casey 1914: 364. Synonymy with S. villosus by Linsley (1963: 91).

Anelaphus davisi Skiles 1985: 308, new synonym (Fig. 8c).

Discussion. The complex of elongate, parallel-sided hardwood twig borers including, originally, Anelaphus villosus (Fabricius) and A. parallelus (Newman), and later, A. davisi Skiles, has been a constant source of confusion because there are no morphological features that consistently allow for discrimation among these taxa. Fabricius’s (1792) original description of villosus (based on a single specimen from “Carolina”) (Fig. 8a) defined the species as follows: “ thorace mutico, obscurus cinereo villosus elytris bidentatis.” Of note is that he described the elytral apices as bidentate. Newman (1840: 28) redescribed villosus in Elaphidion, based on a specimen from St. John’s Bluff, Florida (note that this is also the type locality of another synonym of A. parallelus, A. arctum Newman, which was synonymized by Horn (1885)), and described the elytral apices as “ truncata, utroque angulo spina ”, meaning truncate with both angles spinose. Immediately following the E. villosus account, Newman described Elaphidion parallelum (Fig. 8b), noting the elongate form, parallel elytra, and truncate elytral apices. He had specimens from east Florida, Georgia, and Delaware.

Skiles (1985) was the most recent worker who attempted to discriminate among the adults of this complex. He stated that A. parallelus “is often confused with A. villosus, but is readily separated by its more slender form (elytra over three times as long as broad in parallelus, no more than three times as long as broad in villosus) and the third antennal segment, which is subequal to the fourth in parallelus but distinctly longer than the fourth in villosus.” This was a slight expansion of the characters used by Linsley (1963) and Gosling (1978).

Skiles (1985) added to the complex two additional species, A. davisi (Fig. 8c) and A. belkini (Fig. 1c), both from the Davis Mountains in Texas. Skiles described A. davisi as having the third and fourth antennomeres subequal and said, “from A. parallelus, which it most closely resembles, A. davisi can be distinguished by the more robust form and antennae, the more coarsely punctate metasternum, abdomen, and legs, the reduced antennal spines, and by the emarginate, rather than bispinose elytral apices.” He later conceded that “some of the central Texas specimens [of A. parallelus] exhibit reduced elytral spines and a rather coarsely punctate abdomen. It is thus possible that A. davisi represents an isolated population which is only subspecifically distinct from A. parallelus.”

Lingafelter and Horner (1993) found intergradation in north Texas for specimens identified as parallelus and villosus and treated these under the same species account in their faunal study. In particular, measurements were made of the elytral width to length ratio and it was found that distinctions made by Skiles were not clear. They stated, “There is either intergradation in NCT [north central Texas] between the two species or the given distinction is not valid, perhaps only representing individual variation.”

Gosling’s (1978, 1981) works (also summarized in Solomon 1995) showed biological differences among what he called A. villosus (larvae of which bore into recently dead oaks and other hardwoods, and do not girdle them) and A. parallelus (larvae of which girdle living twigs of oaks, preferentially, but will also use other hardwoods). While Gosling did show two distinct biologies in Michigan, he did not assess whether these biological distinctions are maintained throughout the range of these taxa that occur throughout the eastern half of the United States into west Texas. On this point, some of the type specimens of A. davisi were reared from dead Quercus emoryi Torrey, and this apparent difference in larval biology from A. parallelus was used to justify his description of that species.

Gosling’s contention that biological differences imply species differences is strongly challenged in the ecological and population genetics literature. Generalist species populations often display intraspecific niche diversity through variations in behavior, morphology, and habitat use (Costa-Pereira and Pruitt 2019), and this intraspecific niche variation has been further discussed in Bolnick et al. (2011) and Roughgarden (1972). Significant intraspecific variation in feeding, host-use, and larval behavior has been documented in Drosophila Fallén flies (Sokolowski 1985) and Manduca caterpillars (Smith 2019), among many other animals.

I have examined photographs of the dorsal views of the holotype of Stenocorus villosus Fabricius, a syntype of Elaphidion parallelum Newman, and the holotype of Anelaphus davisi Skiles and determined that any morphological features used by Gosling, Skiles, Chemsak, and others to differentiate these taxa (e.g., proportions of elytra, pronotum, and relative lengths of third and fourth antennomeres) do not show discrete differences. The holotype of Stenocorus villosus Fabricius has elytra 3.24 times longer than wide, antennomere 3 is 98.3% as long as antennomere 4, and the pronotum is equal in length and width. A syntype of Elaphidion parallelum has the elytra 3.26 times longer than wide and the pronotum 1.1 times longer than wide (the ratio of the antennomeres cannot be determined due to their orientation in the photograph, but do not appear significantly distinctive). These proportions demonstrate that they are meaningless to distinguish among the forms. I have examined specimen collected at the same location and time that vary in having truncate or dentiform elytral apices (Pecos Co., Texas) and elytral proportions at both extremes (Gilmer Co., Georgia). While there are populations that apparently exhibit different larval biologies regarding larval girdling and adult oviposition on recently dead versus living hardwoods, I contend that there is widespread support for an alternative conclusion that this is another example of intraspecific variation as has been documented widely and cited above. It is therefore my opinion that the above-mentioned forms represent a single widespread species. The other oak Anelaphus species described by Skiles (1985), A. belkini, is not included in this complex since the structure of the elytral apex (rounded to a spinose suture), antenna (scape and third antennomere weakly sulcate), and pronotum (punctation as coarse as elytral base in both sexes) allow for its morphological distinction.

Another taxon in the complex, Elaphidion rusticum LeConte, has been considered incertae sedis in recent catalogues (Bezark 2019; Monné 2019). Fitch (1859) says, “...our latest authorities place it as a synonym of the Stenocorus villosus of this author [Fabricius 1792]” in his long discussion of putator which was described by Peck (1819), and is itself is now a synonym of Anelaphus villosus in the aforementioned catalogues. Linsley (1963: 96) stated, “Judging from the above description, this species [rusticum] is an Elaphidionoides, probably synonymous with E. villosus (Fabricius) or E. parallelus (Newman).” I therefore remove Elaphidion rusticum LeConte from incertae sedis and place it as a new synonym of Anelaphus villosus (Fabricius).

This species is widespread throughout the eastern United States and Texas. Bezark (2018) recorded one specimen identified as A. davisi from New Mexico. Although Linsley et al. (1961) records one specimen from the Southwestern Research Station, Portal, Arizona, 6 June 1958, extensive collecting has yielded no additional material from Arizona. Many hundreds of specimens have been examined over the past 20 years, but the following records below represent more recent material from throughout the range.

Material examined. Illinois: Cook Co., Palos Park, 10 June 1968 (1, DJHC); Maryland: Montgomery Co., North Potomac, 20 April 1999, S. W. Lingafelter (1, SWLC); New York: Westchester Co., Briarcliff Manor, 20–21 April 1988, J. D. Ryan (1, DJHC); Georgia: Gilmer Co., 269 Creekside Road, Ellijay, 24 May – 1 June 2019, UV/MV lights, R. Morris (4, RFMC); Ohio: Ashland Co., Mohican State Park, 14 July 1979, R. A. Androw (1, DJHC); South Carolina: Pickens Co., Clemson, 27 May 1989, J. K. Moulton (1, DJHC); Texas: Bexar Co., San Antonio, 8734 Paisano Pass, 397 m, 29°41.361 ′ N, 98°39.669 ′ W, 6 April 2018, MV/UV lights, J.E. Wappes & S. W. Lingafelter (2, SWLC); Edwards Co., Choya Ranch W. of Camp Wood, 29°40.665 ′ N, 100°01.330 ′ W, 440 m, 13 April 2018, MV/UV lights, S.W. Lingafelter (1, SWLC); Jeff Davis Co., Davis Mtns. Resort, 5800 ′, 14 June 1991, D. G. Marqua (1, SWLC); Pecos Co., 28 miles S. Ft. Stockton on 385, 1–2 January 1998, reared Quercus mohriana, Morris and Wappes (2, RFMC).