Ligyrus gibbosus

Potential Invader

Common name(s)

carrot beetle

Taxonomy

Family: Scarabaeidae Subfamily: Dynastinae Genus: Ligyrus Species: Ligyrus gibbosus (DeGeer, 1774)

Adult diagnosis

Total body length 11.6–16.5 mm (0.46–0.65 in). Body oblong. Color reddish-brown, rarely shiny black. Clypeus strongly constricted towards acute apex; apex with 2 close-set, apical teeth. Head with weak, transverse ridge on disc; without horns or tubercles. Pronotum with small tubercle near anterior margin; distinct fovea present behind apical tubercle. Apex of last sternite weakly emarginate in male, quadrate in female.

Larval diagnosis

For Ligyrus spp. (Ritcher, 1966): Grub C-shaped, not hump-backed, cylindrical, whitish. Maxilla with galea and lacinia fused or nearly so. Lacinia of maxilla with 3 well developed unci. Maxillary stridulatory teeth truncate. Inner concave surface of mandible, distad of molar area, toothed. Dorsal surface of the last antennal segment with 2–5 sensory spots. Legs 4-segmented. Anal opening transverse, straight or slightly curved. Plegmatia absent.

Native range

North America, southern Canada to Mexico. Ligyrus gibbosus is broadly distributed across North America from the Pacific to Atlantic coasts (Ratcliffe and Paulsen, 2008). It has been recorded in Canada (Bousquet, 1991), throughout the U.S., and as far south as central Mexico (Ratcliffe et al., 2013).

Plant host(s)

This species damages a broad range of plants as both larva and adult. Hayes (1917) recorded larvae feeding on the roots of Amaranthus spp., domestic sunflower (Helianthus annuus), oats (Avena sativa), "pigweed" (Amaranthaceae), and wheat (Triticum spp.). Adults exhibit an even wider dietary range, including carrot (Daucus carota), celery (Apium graveolens), corn (Zea mays), cotton (Gossypium spp.), Dahlia spp., elm (Ulmus spp.), oak (Quercus spp.), sugar beet (Beta vulgaris), and sweet potato (Ipomoea batatas).

Life history

(Hayes, 1917): Eggs are laid in soil, 12.7–15.2 cm deep (5.0–6.0 in), at the base of a host plant. Plants in organic rich soils are preferred. In Kansas, eggs were laid May to July, larvae emerging after an average of 10 days. The larval stage lasts an average of 52 days. The pre-pupal and pupal stages last an average of 7 and 19 days, respectively. Adults are most active May to June, and then again in August, suggesting that there may be multiple generations per season. Adults are nocturnal, hiding in soil during the day. Overwintering adults burrow into the soil to escape freezing.

Pest potential

Significant. Larvae and adults of this species damage a wide range of commercially important plants. Celery, potatoes, sugar beets, and sunflowers may be economically impacted. Sunflowers appear particularly susceptible, with both wild (Ratcliffe and Paulsen, 2008) and domestic (Hayes, 1917) species suffering heavy infestations.

Status in Hawaii

New record, not established. We recorded a single specimen of Ligyrus gibbosus from Oahu (deposited at The Bernice Pauahi Bishop Museum). The specimen label indicates it was discovered dead in a package of dates shipped from Coachella Valley in California in 1934.

Status in Guam

Not established or recorded. There are no records of this species from Guam.

Potential distribution and dispersal pathway

This species is strongly attracted to lights at night and is a strong flier (Ratcliffe and Paulsen, 2008). Thus, it is likely that this beetle would be attracted to well-lit ports and airports. This would allow for hitchhiking on marine or air cargo, as likely occurred with the new record of this species in Oahu.

Similar species

Although Ligyrus gibbosus is the only member of its genus recorded from Hawaii, it is similar to potential future invasive species such as the sugarcane beetle (Tomarus subtropicus) and taro beetles (Papuana spp.). It can be separated from those scarabs by examination of the head that lacks horns or tubercles in L. gibbosus (Papuana spp. often possess horns or tubercles), central disc of the head that has a weak, transverse ridge in L. gibbosus (lacking in T. subtropicus), clypeal apex (L. gibbosus with clypeus constricted with 2 close-set apical teeth versus clypeus broad, never with 2 close-set apical teeth as in Papuana spp.), color (T. gibbosus reddish-brown, rarely black versus Papuana spp. and T. subtropicus always shiny black), and size (T. gibbosus 11.6–16.5 mm [0.46–0.65 in] versus 15.0–25.0 mm [0.59–0.98 in] in Papuana spp. and 20.0–26.0 mm [0.79–1.02 in] in T. subtropicus).

Other names (synonyms)

Bothynus morio (LeConte), Ligyrus californicus (Casey), Ligyrus spissipes (Casey), Ligyrus arizonensis (Casey), Ligyrus bicorniculatus (Casey), Ligyrus brevipes (Casey), Ligyrus breviusculus (Casey), Ligyrus curtipennis (Casey), Ligyrus effetus (Casey), Ligyrus farctus (Casey), Ligyrus lacustris (Casey), Ligyrus laetulus (Casey), Ligyrus laevicauda (Casey), Ligyrus laticollis (Casey), Ligyrus longulus (Casey), Ligyrus lucublandus (Casey), Ligyrus parallelus (Casey), Ligyrus puncticauda (Casey), Ligyrus remotus (Casey), Ligyrus rubidus (Casey), Ligyrus scitulus (Casey), Ligyrus texanus (Casey), Ligyrus virginicus (Casey), Ligyrus laticauda (Casey), Podalgus variolosus Burmeister, Scarabaeus juvencus Fabricius, Scarabaeus gibbosus DeGeer, Tomarus gibbosus (DeGeer)

Special note

The scientific name of this species has undergone considerable change over the last several years. The genera Ligyrus and Tomarus were synonymized in 2002 (Ratcliffe, 2002) but this was challenged in a 2015 publication (Morón and Grossi, 2015).

Report your observation

In Hawaii, this species represents a new invasive species. Prevent the spread of this species by reporting your observation at our iNaturalist project.

Ligyrus gibbosus male; photo by E.L. Engasser

Ligyrus gibbosus male; photo by E.L. Engasser

Ligyrus gibbosus male; photo by E.L. Engasser

Ligyrus gibbosus male; photo by E.L. Engasser

Ligyrus gibbosus male sternites, ventral view; photo by E.L. Engasser

Ligyrus gibbosus male sternites, ventral view; photo by E.L. Engasser

Ligyrus gibbosus female sternites, ventral view; photo by E.L. Engasser

Ligyrus gibbosus female sternites, ventral view; photo by E.L. Engasser

Ligyrus gibbosus male genitalia, caudal view; photo by E.L. Engasser

Ligyrus gibbosus male genitalia, caudal view; photo by E.L. Engasser

Ligyrus gibbosus male genitalia, lateral view; photo by E.L. Engasser

Ligyrus gibbosus male genitalia, lateral view; photo by E.L. Engasser

distribution map for Ligyrus gibbosus

distribution map for Ligyrus gibbosus