Scarabs in Hawaii and the Pacific

The number of scarab pests has risen steadily (Jackson and Klein, 2006). Once established, scarab pests are extremely difficult to dislodge, and a full range of technologies and controls is needed for their eradication (Jackson and Klein, 2006).

The coconut rhinoceros beetle (Oryctes rhinoceros) causes distinctive damage in palm leaves and 50% mortality in afflicted coconut trees (Gressitt, 1953). In Guam, coconut palm losses exceeded $US 2.5 million between 2007 and 2009 (Moore, 2009). In December 2013, this destructive beetle was discovered breeding on Oahu island in Hawaii (Hawaii Department of Agriculture, 2014). The beetle poses a threat to the coconut palm, a tree that is deeply integrated into Hawaii’s traditions, culture, and economy. Some of Hawaii’s most persistent and economically significant pests are foreign scarab species. The long-established Chinese rose beetle (Adoretus sinicus) is an agricultural and horticultural pest with a palate for more than 250 plant species (McQuate and Jameson, 2011). Widespread invasives such as Protaetia species and oriental beetle (Anomala orientalis) (Reding and Klein, 2007) trouble the agriculture and economy in regions where they are introduced. Additionally, tourism is threatened by scarab turf pests such as the southwestern masked chafer (Cyclocephala pasadenae), plate-faced beetle (Temnorhynchus retusus), and Hybosorus roei.

Conservation of native scarabs and the conservation impact of non-native scarabs is an additional concern. Island archipelagos and isolated montane regions harbor many unique scarab beetles. The flightless, endemic Hawaiian stag beetles (Apterocyclus species: Lucanidae) of Kauai have become increasingly rare, with two of the five species now thought to be extinct (Paulsen and Hawks, 2014). Further, non-native scarabs are known to damage rare, native plants on both Hawaii and Guam. On Hawaii, the Chinese rose beetle (Adoretus sinicus) is known to feed on the endangered plants such as kauila (Colubrina oppositifolia), Kauai hau kuahiwi (Hibiscadelphus distans) and koʻoloaʻula (Abutilon menziesii) (Howarth, 1985). On Guam, the oriental flower beetle has been reported as a pest of the endangered Micronesian cycad (Cycas micronesica) (Marler and Muniappan, 2006).

How many scarabs are in Hawaii? Seventy-one species of scarab beetles (chafers, hide beetles, dung beetles, stag beetles, and rhino beetles) are recorded from Hawaii (Nishida, 2002; McQuate and Jameson, 2011; Paulsen and Hawks, 2014). A full checklist of Hawaiian scarabaeoids is available. Only five of these species are native to Hawaii (the Hawaiian stag beetles). Your observations and specimens can assist in advancing our knowledge of Hawaiian scarabs. You can report scarab observations to our iNaturalist project.

How many scarabs are in Guam? Twenty-two scarab beetles (chafers, hide beetles, dung beetles, stag beetles, and rhino beetles) are reported from Guam. Like Hawaii, only a small minority of these species are believed to be native. The majority of Guam's scarabs are widespread adventives such as the Chinese rose beetle (Adoretus sinicus). A full checklist of Guamanian scarabaeoids is available.

What if I find a coconut rhino beetle in Hawaii? Report the coconut rhinoceros beetle (CRB) to the pest hotline at 808-832-0585 (local call in Hawaii) or to our iNaturalist project. The citizen science project “Help Save Hawaii’s Coconut Trees” also needs your input.

What native scarabs are known from Hawaii or Guam? Both Hawaii and Guam have some native scarabaeoid beetles. Guam has both native stag beetles (Lucanidae) and native scarabs (Scarabaeidae). The Marianas stag beetle (Figulus integricollis), can be found in rotting tree logs on Guam and the Northern Mariana Islands (Bourquin, 2002), and the Caroline Islands chafer (Lepidiota carolinensis), is native to many islands across Micronesia including Guam (Cartwright and Gordon, 1971). The Hawaiian island of Kauai is home to a fascinating radiation of stag beetles in the genus Apterocyclus (the Hawaiian stag beetles). These native stag beetles were once common across the island and occurred from sea level to the montane koa forests (Paulsen and Hawks, 2014), and their larvae could be found by the hundreds in the soil around koa trees (Van Dyke, 1922). Now, however, these beetles are confined to highland koa forests, and two of the five species may be extinct (Paulsen and Hawks, 2014).

Are there native dung beetles in Hawaii or Guam? It appears that Hawaii does not host any native dung beetles. The tiny dung beetle Ataenius pacificus was described from Hawaii, but it is originally from the U.S. mainland and was accidently transported to Hawaii. The dung beetles Canthon balteatus and Canthidium muticum were also described from "Hawaii", however this appears to be an error in the original descriptions of the species (Liebherr et al., 2010). Both are known from the Neotropics, and neither species has ever been collected in Hawaii. It is unclear if Guam hosts any native dung beetles. The tiny dung beetle Airapus yasumatsui is recorded from Guam and the Marianas (Cartwright and Gordon, 1971), but the validity of this species is problematic. Until the taxonomy of this tiny beetle is resolved, the question of a native Guamanian dung beetle remains uncertain.

Are Hawaiian scarabs in need of conservation? Sadly, two of the five species of endemic Hawaiian stag beetles may be extinct (Paulsen and Hawks, 2014). These showy and large beetles (some over 2 cm) are icons for Kauai’s native Acacia koa forest. All species are flightless, rare, and dependent upon vanishing native Hawaiian habitat. These native stag beetles suffer from a combination of habitat loss and heavy predation from non-native rodents (Howden, 2008) and probably pigs. Larvae could once be found by the hundreds in soil around decaying koa trees (Van Dyke, 1922). All species are in urgent need of conservation and study.

Are checklists available for scarabaeoid beetles of Hawaii and Guam? Yes! We provide a checklist to Hawaiian scarabaeoids as well as a checklist to Guamanian scarabaeoids.

About scarab beetles