Agathidium pulchrum, LeConte, 1853

MILLER, KELLY B. & WHEELER, QUENTIN D., 2005, Slime-Mold Beetles Of The Genus Agathidium Panzer In North And Central America, Part Ii. Coleoptera: Leiodidae, Bulletin of the American Museum of Natural History 2005 (291), pp. 1-167 : 24

AGATHIDIUM PULCHRUM SPECIES GROUP

DIAGNOSIS: Members of this species group are characterized by having the mesosternum strongly concave (declivitous), the clypeus strongly excavate to extending moderately beyond the sides of front of cranium (e.g., figs. 6, 22), the metasternum not strongly shortened, the humeral angles of the elytra relatively distinct, the postocular temporum relatively short (e.g., figs. 6, 22), and males of several species with a prominent tusk or horn on the left mandible (e.g., figs. 21–29, 44, 45). Several of the species are distinctly and dramatically maculate dorsally (figs. 44– 46, 48–51), which is unusual for New World members of Agathidium . The tarsal formula is Ƌ 5­5­4 / ♀ 5­4­4 or 4­4­4.

DESCRIPTION: This group includes species belonging to the subgenus A. (Neoceble) Gozis auctorum , a very diverse Holarctic group. The presence of a horn on the male left mandible (also occurring in our A. brevisternum and some of our A. concinnum group species) is a particularly unique feature of several of these species in the Leiodidae and in beetles in general. Asymmetry in similar secondary sexual features is only rarely reported. The horn comes in a variety of shapes and sizes when fully developed, including those that are short, spinous, and adpressed (figs. 29, 30) to very long and variously curved (figs. 21–23, 44, 45). One species, A. aristerium , has the apex of the mandible strongly upturned and truncate apically (fig. 25, 26). In several species the mandibular horn bears a prominent brush of setae arising apically from an oblique, curved impressed line, but not all species have a setose horn. In all species where sufficient material is available for examination, the horn is variable from entirely absent to well developed. In some species, very many males are strongly modified, whereas in some very few males are modified. The development of this dimorphism is particularly dramatic in one species, A. marae , in which not only is there a left mandibular horn, but the right surface of the frons is also developed into an opposing spine (figs. 23, 24). No evidence has yet been presented for a function for the mandibular horn, but other beetles with horns use them for male­male competition, a possible scenario for these species where large numbers of males and females are often concentrated on a small food and oviposition resource where competition for mates might figure strongly. Historically, many species were recognized based on the presence or absence of a male mandibular horn, but the variability of this feature within all species that possess it makes this an unreliable character for keying or diagnosing species. In the past, species identifications have also relied heavily on the number of female protarsomeres (5 or 4). Although this is a good diagnostic feature of some species, we have avoided using this character as an exclusive diagnostic character since it is not always possible to positively associate males with females. It seems apparent from previous work on the group that often female and males were misassociated, leading to erroneous conclusions about the tarsal formula for females of certain species.

Most of these species occur in forests of western and northern North America. There is an additional assemblage of species in northeastern North America and a few that occur only in the central portion of the continent.

KEY TO A. PULCHRUM SPECIES