Heterocerus mollinus Kiesenwetter, 1851

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 : 22-23

9. Heterocerus mollinus Kiesenwetter

( Fig. 20 , 41 , 62 )

Heterocerus mollinus Kiesenwetter 1851: 289 .

Lanternarius mollinus (Kiesenwetter) : Pacheco 1964: 66.

Description. Length 4.0 - 5.5 mm. Dark red to dark brown. Apical angles of pronotum usually pale. Pale elytral markings distinct and often trifaciate with two basal, one median, and two apical light marks ( Fig. 20 ); markings variable, in extreme cases basal and medial elytral markings lacking; striae vaguely indicated. Post-metathoracic coxal lines absent, post-mesothoracic coxal lines prominent. Male genitalia ( Fig. 41 ) of the typical Heterocerus type, phallobase gradually narrowed anteriorly to approximately 75% of its greatest width; median plate, in anterior half, linear and positioned on left side of the midline of the phallobase; parameres triangular with rounded apices, their medial edges only slightly divergent anteriorly and separated by about half the width of one paramere; dorsal plate nearly circular, with a small sclerotized cleft on its left anterior edge. Perhaps half of all male specimens are indistinguishable from females externally, but the remainder show some degree of mandibular enlargement, with about 10% being truly hypermandibulate.

Diagnosis. This species is similar in general appearance to two other southeastern species that have post-mesothoracic coxal lines, H. sinuosus and H. insolens . Similar coloration of the pronotum and elytra distinguishes H. mollinus from H. sinuosus , in which the pronotum is lighter than the elytra ( Fig. 19 ). Heterocerus mollinus is very similar to H. insolens and is most easily distinguished by examination of the male genitalia. The gradually narrowed phallobase of H. mollinus immediately distinguishes it from H. insolens , in which there is a more abrupt constriction ( Fig. 42 ). Generally, specimens of H. insolens often can be distinguished from H. mollinus by the elytral pattern. The median and distal pale markings are less extensive in H. mollinus (compare Figures 18 and 20 ).

Notes. This is the most common species of Heterocerus in the eastern United States. Thousands of specimens can be collected in light traps placed near muddy river banks. During this study, much of the labor required during the processing of light trap samples involved distinguishing other species of heterocerids from the huge numbers of H. mollinus present. Miller (1988b) coined the term king males for male specimens of H. mollinus that have a dorsal horn protruding from the surface of the mandibles, as well as being hypermandibulate to an exaggerated extent. No king males were found among the thousands of specimens examined during this study.

Heterocerus mollinus has been collected from a wide range of habitats throughout Mississippi. This, and Tropicus pusillus , are the only heterocerids in the study area that are often collected from nonriverine environments, such as roadside ditches. It is common near rivers and ponds of all sizes.

Distribution. Heterocerus mollinus occurs throughout North America, except northern Canada. It occurs throughout the study area ( Fig. 62 ), but appears to be less common near the Atlantic Coast and in Florida. Specimens examined from five localities in Georgia and two in Florida represent new state records (See Appendix).

Specimens examined. 1,931, not including approximately 19,900 collected 26 May 2005, Jefferson County Mississippi, Flathead Lake, N 31 o 50.706', W -91 o 12.899'. (See Appendix).

Figures

Figures 18-20. Habiti of large Heterocerus species with post-mesocoxal lines. 18) H. insolens. 19) H. sinuosus. 20) H. mollinus. Specimens 20a and 20c are hypermandibulate. 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 58-65. Distribution by county in the United States. 58) Heterocerus fatuus. 59) Heterocerus sandersoni. 60) Heterocerus intermuralis. 61) Heterocerus angustatus. 62) Heterocerus mollinus. 63) Heterocerus selanderi.64) Distribution of Heterocerus sinuosis by county in Mississippi. 65) Distribution of Heterocerus collaris by county in the United States.