Tomarus subtropicus

Potential Invader

Common name(s)

sugarcane beetle, sugarcane grub

Taxonomy

Family: Scarabaeidae Subfamily: Dynastinae Genus: Tomarus Species: Tomarus subtropicus (Blatchley, 1922)

Adult diagnosis

Total body length 20.0–26.0 mm (0.79–1.02 in). Body oblong. Color shiny black. Clypeus constricted towards parabolic apex; apex with 2 close-set, apical teeth. Head lacking 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 emarginated in male, quadrate in female.

Larval diagnosis

For Tomarus (Ritcher, 1966): Grub C-shaped, not hump-backed, cylindrical, cream-colored. 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 straight or slightly curved. Plegmatia absent.

Native range

Southeastern U.S. This species is found from North Carolina south through Florida and east to Alabama (Buss, 2003).

Plant host(s)

In its native range, larvae of this species are well-documented pests of sugarcane and turf grasses (Buss, 2003). Kostromytska and Buss (2011) investigated the suitability of different turf grasses as larval host plants. They found that the warm season turf grasses including palmetto saint augustine grass (Stentaphrum secundatum), ‘tifway’ bermuda grass (C. dactylon x transvaalensis), ‘empire’ zoysia grass (Zoysia japonica), common centipede grass (Erimochloa ophiuroides),‘pensacola’ bahia grass (Paspalum notatum), and ‘sea dwarf’ seashore paspalum (Paspalum vaginatum) were all suitable hosts. However, larvae failed to thrive on the cool season turf grasses including ‘gulf’ annual ryegrass (Lolium multiflorum).

Life history

In Florida, there is a single generation each year. Adults are active April through June, with numbers peaking in May and June when eggs are laid (Buss, 2003). The final instar is found from October to April. Pupation takes place in a subterranean pupal cell (Buss, 2003). Females of this species strongly prefer to lay eggs in "mucky" organic rich soils. Larvae are rarely found in sandy sites (Cherry and Coale, 1994).

Pest potential

Significant. Larvae of this species are serious and destructive pests of grasses (Buss, 2003). In Florida, Tomarus subtropicus is the single most important scarab pest of sugarcane and is able to reduce yields by more than a third (Cherry and Coale, 1994). The species also damages a variety of turf grasses (Kostromytska and Buss, 2011).

Status in Hawaii

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

Status in Guam

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

Potential distribution and dispersal pathway

Because larvae feed on turf roots, it is possible that larvae or eggs could be transported in shipments of commercial turf. Other Tomarus species are known to fly to lights at night (Ratcliffe and Paulsen, 2008), and it is likely that this beetle is attracted to well-lit ports and airports. This would allow for hitchhiking on marine and air cargo.

Similar species

This species is similar to the carrot beetle (Ligyrus gibbosus) recorded on Oahu and the potential future invaders, the taro beetles (Papuana spp.). It can be separated from those scarabs by examination of the head (T. subtropicus without horns or tubercles versus Papuana spp. that often possess horns or tubercles), central disc of the head (T. subtropicus lacking a transverse ridge versus a weak, transverse ridge in L. gibbosus), clypeal apex (T. subtropicus clypeus constricted with 2 close-set apical teeth versus clypeus broad, never with 2 close-set apical teeth in Papuana spp.), color (T. subtropicus is shiny black versus reddish-brown in L. gibbosus), and size (T. subtropicus is 20.0–26.0 mm [0.79–1.02 in] versus L.. gibbosus at 11.6–16.5 mm [0.46–0.65 in]).

Other names (synonyms)

Ligyrus subtropicus Blatchley

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.

Tomarus subtropicus female; photo by E.L. Engasser

Tomarus subtropicus female; photo by E.L. Engasser

Tomarus subtropicus female; photo by E.L. Engasser

Tomarus subtropicus female; photo by E.L. Engasser

Tomarus subtropicus male sternites, ventral view; photo by E.L. Engasser

Tomarus subtropicus male sternites, ventral view; photo by E.L. Engasser

Tomarus subtropicus female sternites, ventral side; photo by E.L. Engasser

Tomarus subtropicus female sternites, ventral side; photo by E.L. Engasser

Tomarus subtropicus male genitalia, caudal view; photo by E.L. Engasser

Tomarus subtropicus male genitalia, caudal view; photo by E.L. Engasser

Tomarus subtropicus male genitalia, lateral view; photo by E.L. Engasser

Tomarus subtropicus male genitalia, lateral view; photo by E.L. Engasser