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Coleoptera of Great Smoky Mountains National Park Species Pages

Family Nitidulidae

            Subfamily Nitidulinae

 Psilopyga nigripennis LeConte

The stinkhorn beetle

Adult.

Mature larva.

 

Description and Taxonomy

Description. Adult length 6-7mm.  This robust, orange and black nitidulid is unlikely to be mistaken for any other member of the family. The prominent, posteriorly projecting prosternal process, deeply bilobed labrum, and shiny non-pubescent dorsal surface of the body will distinguish the genus from others if any doubt exists (Habeck 2002). The orange and black coloration and the slightly larger size distinguish it from its otherwise similar congener P. histrina

Mature larval length 12-15mm, body unpigmented and unsclerotized, soft and maggot-like, spiracular snorkels elongate, subequal to legs on abdominal segments. Urogomphi simple and short. The close association with stinkhorn mushrooms is the most reliable clue to identifying larvae of Psilopyga species. Alcohol preserved larvae are coated with coagulated slime (removed from specimen pictured above), either from the feeding substrate or produced by the larva. 

Four species of Psilopyga are known from North America (Parsons 1943). These species are often incorrectly placed under the name Oxycnemus Erichson in collections and faunal survey listings. 

Life History

This species and P. histrina are closely associated with stinkhorn mushrooms and often co-occur on the same host. Specimens from GSMNP have thus far been collected on the netted stinkhorn, Dictyophora duplicata (images and information on this species). Adults can be found around the base of the mushroom or in adjacent leaf litter while in the "egg" stage or actively sporulating. The stiinkhorn fruiting body collapses within a day or two and larvae of P. nigripennis mature completely immersed in the pool of viscous, gelatinous residue that remains. Only their spiracular snorkels protrude for gas exchange. They appear to feed more or less constantly while slowly moving through this substrate. Larvae grow from 5mm to a maximum of 15mm within only four or five days and presumably pass through three instars. Larvae produce their own slime secretions in addition to the substance in which they live. This information is based on observations I made at Purchase Knob, on the southeastern boundary of the Park, during August 2002. I was not able to get any to pupate. An extensive discussion of  phallophagy (=stinkhorn feeding) in nitidulid beetles and its phylogenetic implications can be found in Leschen (1999). This species is also recorded from Phallus impudicus (Parsons 1943).

I was suspicious that this species and P. histrina may represent a single species with a marked color dimorphism because they are often found on the same host mushroom and have no obvious external differences other than color. Dissections of male genitalia revealed small but obvious differences in the shapes of the tegmens and components of the internal sacs of the two species, confirming that they are indeed separate species.

Distribution

This species occurs in  northeastern U.S. from North Carolina to New Hampshire and west at least to Indiana (Parsons 1943). Presumably it is more widespread in GSMNP than current records indicate. 

Conservation Concerns

The species is not known to be under threat.

Mature larva of P. nigripennis as seen submerged in collapsed stinkhorn "slime." Photo, Ernest Bernard.

Exposed larvae of P. nigripennis. Photo, Ernest Bernard.

 

Locality records in GSMNP.

Acknowledgements

Development of these pages was supported by grants from Discover Life in America and the National Science Foundation (DEB-0516311). Photographs of larvae in substrate by Ernest Bernard.

References

Habeck, D. H. 2002. Nitidulidae. pp. 311-315 in R. H. Arnett, Jr., M. C. Thomas, P. E. Skelley, and J. H. Frank (eds.). American Beetles, Vol. 2. CRC Press, New York, NY.

Leschen, R. A. B.  1999.  Systematics of Convex Nitidulinae (Coleoptera: Nitidulidae): Phylogenetic Relationships, Convexity, and the Origin of Phallalophagy. Invertebrate Taxon 13: 845-882.

Parsons, C. T.  1943.  A revision of Nearctic Nitidulidae  (Coleoptera). Bulletin of the Museum of Comparative Zoology 92: 119-278 + 13 pls.

Posted 21 Sep. 2006, C. E. Carlton, Louisiana State Arthropod Museum.

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