Heterocerus gnatho LeConte, 1863

King, Jonas G. & Lago, Paul K., 2012, The variegated mud-loving beetles (Coleoptera: Heteroceridae) of Mississippi and Alabama, with discussion and keys to the species occurring in the southeastern United States, Insecta Mundi 2012 (275), pp. 1-53 : 16

2. Heterocerus gnatho LeConte

( Fig. 14 , 38 , 55 )

Heterocerus gnatho LeConte 1863: 74 .

Neoheterocerus gnatho (LeConte) : Pacheco 1964: 85.

Description. Length 3.5 - 7.0 mm. Dark brown to yellowish brown. Elytra dominated by pale markings that are highly variable in shape and definition, vaguely trifasciate ( Fig. 14 ); striae absent. Pronotal disc usually darker than elytra, apical angles of the pronotum pale, apical spot sometimes elongated posteriorly along pronotal border, narrowing posteriorly only slightly. Post-metathoracic coxal and post-mesothoracic coxal lines absent. Male genitalia ( Fig. 38 ) of the typical Heterocerus type, parameres triangular; dorsal plate of aedeagus depressed on the right anterior edge, and convex on its posterior edge. Hypermandibulate males common.

Diagnosis. Heterocerus gnatho is the largest heterocerid species in North America, although its size varies considerably. While strikingly similar in appearance to H. pallidus , H. gnatho is generally darker and has less prominent light pronotal borders. Enough variation is present in these characters, however, to warrant inspection of male genitalia. A strong notch on the posterior edge of the dorsal plate (compare dorsal views in Fig. 37 and 38 ), and having the interior margins of the parameres diverging slightly from one another, distinguish this species.

Notes. Southeastern records are mostly from sandy riverine and coastal areas.

Upon inspection of the male genitalia in previously identified material, it was found that specimens of H. intermuralis and H. pallidus were commonly misidentified as H. gnatho . This is an easy error to make if one uses Miller’s (1996) key. Undoubtedly, some published records for this species are erroneous.

Distribution. Heterocerus gnatho occurs primarily in the northern United States and southern Canada, being most common from southern Ontario to British Columbia in Canada and west of the Rocky Mountains in the United States ( Fig. 55 ). Scattered records exist for Kansas, Iowa, Illinois and North Dakota (New State Record - Pembina Co., ND, Goschke Dam, Tongue River Game Management Area, 28 June 1974, Paul K. Lago; Richland Co., ND, Walcott Dunes, 28 May 1974, Paul K. Lago). In Mississippi, specimens were collected near freshwater and saline habitats along the Mississippi Gulf Coast, at a UV light in Ocean Springs (Harrison Co.), and along the Mississippi River (Great River Road State Park) in Bolivar County.

Specimens examined. 119 (See Appendix).

Figures

Figures 11-17. Habiti of large Heterocerus species lacking post-mesocoxal lines. 11) H. pallidus (male is hypermandibulate). 12) H.intermuralis (male is hypermandibulate). 13) H.fatuus. 14) H. gnatho. 15) H.longilobulus. 16) H. sandersoni. 17) H. angustatus.Scale line = 1mm.

Figures 32-44. Male genitalia of southeastern Heterocerus species. The ventral view is shown unless otherwise stated. 32-39) Species that lack post-mesocoxal lines. 32) H. fatuus. 33) H. glicki. 34) H. intermuralis. 35) H. angustatus; left - ventral view, right - dorsal view. 36) H. longilobulus. 37) H. pallidus; left - ventral view, right - dorsal view. 38) H. gnatho; left - ventral view, right - dorsal view. 39) H. sandersoni; left - ventral view, center - dorsal view, left - lateral view. 40-44) Species with post-mesocoxal lines. 40) H. sinuosus; left - dorsal view, right - ventral aspect. 41) H. mollinus. 42) H. insolens; left - dorsal view, right - ventral aspect. 43) H. parrotus. 44) H. brunneus.

Figures 54-57. Distribution by county in the United States. 54) Heterocerus pallidus. 55) Heterocerus gnatho. 56) Heterocerus longilobulus. 57) Heterocerus insolens.