Casey's June beetle

Casey's June beetle
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Coleoptera
Family: Scarabaeidae
Subfamily: Melolonthinae
Tribe: Melolonthini
Genus: Dinacoma
Species: D. caseyi
Binomial name
Dinacoma caseyi
Blaisdell 1930

Casey's June beetle, Dinacoma caseyi, is a beetle in the scarab family (Scarabaeidae). It is listed as an endangered species with approximately 587 acres (237 hectares) of land as critical habitat in Riverside County, California.[1]

Taxonomy

The genus Dinacoma includes two described species, D. caseyi and D. marginata.[2] Delbert La Rue, a researcher experienced with the genus Dinacoma and a taxonomic expert stated, "Dinacoma caseyi is a distinct species morphologically and comprises its own species group—the caseyi complex—the other [species group] being the marginata complex which includes the bulk/remainder of the genus".[3] The Casey's June beetle was first collected in the city of Palm Springs, California, in 1916, and was later described by Blaisdell (1930, pp. 174–176) based on male specimens. This species measures 0.55 to 0.71 inches (in) (1.4 to 1.8 centimeters (cm)) long, with dusty brown or whitish coloring, and brown and cream longitudinal stripes on the elytra (wing covers and back).

In 2006, entomologists discovered two apparently new species or subspecies of Dinacoma, collected respectively from near the city of Hemet, California, and in the northwest portion of Joshua Tree National Park, California, at Covington Flats.[4] As of 2007, these specimens of Dinacoma have not been formally described in the scientific literature, but expert evaluation places them in the other Dinacoma species group (marginata complex).[3] La Rue (2006, p. 2) stated that Dinacoma caseyi is the most morphologically divergent and distinct species in the genus. The new specimens collected from the Hemet area are paler than Casey’s June beetle specimens and possess morphologically different genitalia.[5] Furthermore, the Little San Bernardino Mountains geographically isolate the new Dinacoma Joshua Tree population from all other known Dinacoma species.

Biology

Based on surveys conducted to assess the species' presence, both male and female Casey's June beetles emerge from underground burrows sometime between late March and early June, with abundance peaks generally occurring in April and May.[6] Females are always observed on the ground and are considered flightless.[7] La Rue (2006, p. 1) stated that "Female Dinacoma are very rare in collections. Females display an accentuated sexual dimorphism characterized by an enlarged abdomen, reduced legs and antennae, and metathoracic wing reduction and venation. These characters are likely adaptations to flightlessness and a fossorial biology." During the active flight season, males emerge from the ground and begin flying near dusk.[8] Males are reported to fly back and forth or crawl on the ground where a female beetle has been detected.[9] Cornett (2003, p. 5) theorized that after emergence, females remain on the ground and release pheromones to attract flying males. After mating, females return to their burrows or dig a new burrow and deposit eggs. Excavations of adult emergence burrows revealed pupal exuviae (casings) at depths ranging from approximately 4 to 6 in (10 to 16 cm).[10]

The larval cycle for the species is likely 1 year, based on the absence of larvae (grubs) in burrows during the adult flight season.[3] The food source for Casey's June beetle larvae while underground is unknown, but other species of June beetle are known to eat "plant roots or plant detritus and associated decay organisms".[3] La Rue (2006, pp. 1–2) stated, "[Casey's June beetle] exhibits no specific host preferences, and larvae likely consume any available organic resources— including [layered organic debris]— encountered within the alluvial habitat." Specific host plant associations for Casey’s June beetle are not known. Although visual surveys have detected a concentration of emergence burrows in the vicinity of a number of species of woody shrub in Palm Canyon Wash, this may be due to low soil disturbance by vehicles, foot traffic, and horses near woody vegetation.[8]

Notes

  1. 1 2 Fish and Wildlife Service 2011, p. 58954.
  2. ↑ Blaisdell 1930, pp. 171–176.
  3. 1 2 3 4 La Rue 2006, p. 1.
  4. ↑ La Rue 2006, p. 2.
  5. ↑ Anderson 2006, p. 1.
  6. ↑ Duff 1990, p. 3; Barrows 1998, p. 1
  7. ↑ Duff 1990, p. 4; Frank Hovore and Associates 1995, p. 7; Hovore 2003, p. 3
  8. 1 2 Hovore 2003, p. 3.
  9. ↑ Duff 1990, p. 3.
  10. ↑ Frank Hovore and Associates 1995, p. 6.
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References

 This article incorporates public domain material from the United States Fish and Wildlife Service document "Endangered and Threatened Wildlife and Plants; 12-Month Finding on a Petition To List the Casey’s June Beetle (Dinacoma caseyi) as Endangered With Critical Habitat".

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