Papuana

Potential Invader

Common name(s)

taro beetles

Taxonomy

Family: Scarabaeidae Subfamily: Dynastinae Genus: Papuana

Adult diagnosis

Papuana is a genus of medium-sized scarab beetles that are armed with horns or tubercles. All species are shiny black and have an elongated, oval body shape. Total body length ranges between 15.0–30.0 mm (0.59–1.18 in). The apex of the clypeus is broad and never has 2 teeth close together. Both males and females have either tubercles or horns on the clypeus. Males of many species also have horns or tubercles on the pronotum. Horns, if present, are often reduced in females. The apex of the last sternite is emarginate in male and rounded in the female.

Larval diagnosis

Undescribed. For Dynastinae (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. Legs 4-segmented. Anal opening transverse, straight or slightly curved. Plegmatia absent.

Native range

Indo-Pacific. All 19 described species (Aloalii et al., 1993) are native to the Indo-Pacific area. Two species are known from the Philippines, one from the Moluccas, one from northern Australia, 14 from New Guinea, four from the Solomon Islands, and two from Vanuatu (Aloalii et al., 1993).

Plant host(s)

While the best known plant host of the taro beetles (Papuana) is taro (Colocasia esculenta), other plants in the aroid family (Araceae) are also acceptable hosts including Alocasias spp., Cyrtosperma spp., and elephant ear (Xanthosoma sagittifolium). A number of non-aroids are also recorded as hosts: Angiopteris spp., banana (Musa spp.), cabbage (Brassica oleracea), cocoa (Theobroma cacao), coconut (Cocos nucifera), coffee (Coffea arabica), Crinium spp., Marattia spp., nut palm (Areca catechu), oil palm (Elaeis guineensis), peanuts (Arachis hypogea), pineapple (Ananas comosus), potato (Solanum tuberosum), purple yam (Dioscorea alata), sugarcane (Saccharum officinarum), sweet potato (Ipomoea batatas), tea (Camellia chinensis), and white yam (Dioscorea rotundata) (Aloalii et al., 1993; Lal et al., 2008).

Life history

(Lal et al., 2008): Eggs are laid in moist, organic, rich soils. For Papuana uninodis, larvae emerge after an average of two weeks. The first instar lasts an average of two weeks, the second instar 4–5 weeks, and the final instar 3–4 months. The entire pre-adult lifecycle lasts 17–28 weeks, varying with temperature and humidity. Adults can live as long as 22 months, during which time females lay about 140 eggs. Adults feed by boring into the corm of a variety of aroids. Larvae do not appear to cause direct plant damage. Instead, they feed on detritus and other organic soil debris.

Pest potential

Significant. Of the 19 species of taro beetles (Papuana), eight are major taro pests (Aloalii, 1993). In Fiji and Papua New Guinea, these beetles reduce yields by up to one third, and this has led to the abandonment of many taro farms (Lal et al., 2008). Damage is caused by adults that bore into the taro corm (or root) and cause serious damage. Further, Papuana spp. have a history of invasive establishment beyond their native range. Papuana hubneri, a species native to New Guinea, spread to Kiribati in 1934 and to Fiji by 1984 (Aloalii et al., 1993).

Status in Hawaii

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

Status in Guam

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

Potential distribution and dispersal pathway

While it is unclear how Papuana hubneri first arrived to Fiji and Kiribati, it is not difficult to imagine these scarabs hitchhiking on commercial shipments of taro or other host plants. Similar to other dynastine scarabs that are attracted to lights at night (Ratcliffe and Paulsen, 2008), it is likely that this beetle would be attracted to well-lit ports and airports. This would allow for hitchhiking on marine and air cargo. Because taro is cultivated throughout the Pacific, and beetles damage a broad range of economically important plants, Papuana spp. should be regarded as a significant potential biosecurity hazard in both Hawaii and Guam.

Similar species

Scarabs most likely to be confused with this genus are members of the genera Ligyrus and Tomarus. While not recorded on Guam, the carrot beetle (Ligyrus gibbosus) has been found on Oahu, and other species such as the sugarcane beetle (Tomarus subtropicus) may arrive in the future. Papuana spp. may be distinguished from Tomarus by examination of the head (Papuana spp. usually with horns or tubercles on head versus L. gibbosus and T. subtropicus never with horns or tubercles) and clypeal apex (Papuana spp. never with 2 close-set apical teeth versus clypeus constricted with 2 close-set apical teeth in L. gibbosus and T. subtropicus).

Other names (synonyms)

none known

Report your observation

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

Papuana uninodis male; photo by E.L. Engasser

Papuana uninodis male; photo by E.L. Engasser

Papuana uninodis male; photo by E.L. Engasser

Papuana uninodis male; photo by E.L. Engasser

Papuana lansbergei male; photo by E.L. Engasser

Papuana lansbergei male; photo by E.L. Engasser

Papuana lansbergei male; photo by E.L. Engasser

Papuana lansbergei male; photo by E.L. Engasser

Papuana biroi male; photo by E.L. Engasser

Papuana biroi male; photo by E.L. Engasser

Papuana biroi male; photo by E.L. Engasser

Papuana biroi male; photo by E.L. Engasser