Onthophagus incensus

Beneficial

Common name(s)

none known

Taxonomy

Family: Scarabaeidae Subfamily: Scarabaeinae Genus: Onthophagus Species: Onthophagus incensus Say, 1835

DNA barcode

DNA barcode available: specimen information

Adult diagnosis

Total body length 6.5–12.0 mm (0.25–0.47 in). Body shape oval; may be caked in dung. Color shiny black, with bluish or greenish hues under bright light. Small to medium-sized dung beetle, over 6 mm. Clypeal apex of major male produced, quadrate or trapezoidal; comparatively rounded in minor male and female. Head of major male with 2 slightly curved, vertically-oriented horns that are not connected by a ridge and with apices that are not bifurcate; minor male with horns reduced or replaced by straight, transverse ridge; female with transverse ridge near base. Ocular canthus completely dividing eye. Pronotum of major male with hump-like process; minor male with hump reduced to small bi-lobed process; female lacking process. Pronotum with anterior angles rounded in both sexes. Front tibia of male slightly slender and elongate, female tibia comparatively stout. Scutellum absent.

Larval diagnosis

(Huerta et al., 2010): Grub C-shaped, hump-backed, cylindrical, and cream-colored. Maxilla with galea and lacinia distinctly separate. Labium hypopharynx glossa with 4 or 5 setae of the lateral lobe; 9–12 setae and 4 macrosensilla on the central lobe. Lacinia with 2 or 3 dorso-basal setae. Maxillary palps with single setae. Maxillary stridulatory area with a row of 8 short, conical teeth. Cardo with 3 external setae. Epipharynx with tormae united mesally. Epipharyngeal phoba with teeth small and conical; chaetoparia with 2 or 3 setae. Epicranial stem shallowly forked basally on frons. Antennae 4-segmented, distal segment much reduced. Legs 2-segmented. Prothoracic shield without anteriorly projecting processes.

Native range

United States to Ecuador. This species is recorded from Texas through Mexico and Central America southward to Venezuela and Ecuador (Huerta and García-Hernández, 2013).

Plant host(s)

None. This species feeds on dung as both an adult and larva. There are no records of this beetle feeding on live plant tissues.

Life history

(Huerta and García-Hernández, 2013; Huerta et al., 2010): This diurnal species is associated with pasture land near tropical forests. After locating suitable dung, adults construct a gallery of tunnels 5–15 cm (1.9–5.9 in) beneath the fecal source. Tunnels are provisioned with dung in the form of brood balls. Each brood ball is impregnated with an egg and larval development occurs within. The number of brood balls appears to be seasonally dependent, increasing with onset of the rainy season. Development from egg to adult is about 38 days. There are multiple generations per year.

Pest potential

None. This species recycles dung and is beneficial for ranching and farming in Hawaii. Being a dung feeder, this species has never been recorded damaging crops or ornamental plants. Additionally, this species is not a threat to native dung beetles because none occur in Hawaii or Guam.

Status in Hawaii

Established. This species was introduced to Big Island and Oahu in 1923 to help control populations of the horn fly (Haematobia irritans), a biting pest of livestock (Markin and Yoshioka, 1998). It is fairly common on Oahu (mostly above 500 m) but less abundant on Big Island (Markin and Yoshioka, 1998).

Status in Guam

Recorded, not established. This species was released on Guam in 1953 to help control populations of the horn fly (Haematobia irritans), a biting pest of livestock (Peterson, 1956). However, it failed to establish on the island (Cartwright and Gordon, 1971; Bourquin, 2002).

Potential distribution and dispersal pathway

In both Hawaii and Guam, this species was intentionally imported.

Similar species

This dung beetle could be confused with similarly colored, small to medium-sized (more than 6 mm) Onthophagus species such as Onthophagus binodis, Onthophagus cuniculus, Onthophagus laminatus, Onthophagus armatus, and Onthophagus comperei.

Major males of O. incensus are most readily distinguished by examining the head armature (O. incensus with two slightly curved, vertically-oriented horns that are not connected by a ridge, with apices not bifurcate versus O. binodis, and O. cuniculus that both lack horns, O. comperei with sinuate horns that are weakly bifurcate, O. laminatus that has a distinct ridge between the horns, O. armatus with bisinuate horns connected by a distinct ridge).

Females can be separated by examining the base of the head (O. incensus with transverse ridge versus O. binodis and O. cuniculus with a slightly curved ridge, O. armatus with feebly bisinuate ridge, O. comperei with two tubercles), the pronotal process (O. incensus without a process versus O. binodis and O. laminatus with a small lobe-like process, O. cuniculus with a bi-lobed process), and the anterior pronotal angle (O. incensus with anterior angle rounded versus O. cuniculus and O. laminatus with the anterior angle curved outward).

Other names (synonyms)

none known

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Onthophagus incensus male; photo by E.L. Engasser

Onthophagus incensus male; photo by E.L. Engasser

Onthophagus incensus male; photo by E.L. Engasser

Onthophagus incensus male; photo by E.L. Engasser

Onthophagus incensus male; photo by E.L. Engasser

Onthophagus incensus male; photo by E.L. Engasser

Onthophagus incensus male; photo by E.L. Engasser

Onthophagus incensus male; photo by E.L. Engasser

Onthophagus incensus female; photo by E.L. Engasser

Onthophagus incensus female; photo by E.L. Engasser

Onthophagus incensus female; photo by E.L. Engasser

Onthophagus incensus female; photo by E.L. Engasser

distribution map for Onthophagus incensus

distribution map for Onthophagus incensus