coconut rhinoceros beetles
Family: Scarabaeidae Subfamily: Dynastinae Genus: Oryctes
Scarabs of the genus Oryctes are somewhat uniform in color and armature, but more variable in body shape. Body length ranges between 22.0–77.0 mm (0.86–3.03 in). The body form of these beetles is usually convex dorsally, but varies from elongate and somewhat cylindrical to oblong and weakly flattened dorsoventrally. Color is more uniform, ranging from dark brown to black. While the size of the cephalic horn varies considerably between species, horn shape is similar with all males (and females in many species) having a single, unbranched (ending in one point), curved horn. In many species, sexes can be differentiated based upon the cephalic horn, with females either lacking horns or with a reduced horn. The form of the ocular canthus is variable, being simple in some species or quadrately produced in others. Both males and females of most species possess a broad, sculpted depression on the pronotum.
Undescribed at the generic level. For Dynastinae (Ritcher, 1966): When alive, larvae are firm to the touch (not distinctly "squishy" as in Protaetia spp. with which they may be confused), and they are not able to crawl on their back (a characteristic of Protaetia spp.). 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 to slightly curved. Plegmatia absent.
Old World. Oryctes spp. are distributed widely across the Old World. Species are distributed from western Europe and Scandinavia southward to the African Cape region and eastward across Asia to the Pacific islands (Dechambre and Lachaume, 2001).
Many members of this genus are associated with palms (Dechambre and Lachaume, 2001) including economically important species such as African oil palm (Elaeis guineensis) and coconut palm (Cocos nucifera) (Molet, 2013). Both Oryctes rhinoceros and Oryctes monocerus damage a range of palm and non-palm plant species (Bedford, 2015; Dechambre and Lachaume, 2001). Oryctes rhinoceros in particular, is known to attack non-palms such as the Alexandria laurel (Calophyllum inophyllum), banana (Musa spp.), breadfruit (Artocarpus spp.), mango (Mangifera spp.), pineapple (Ananas comosus), and sugarcane (Saccharum spp.) (Molet, 2013).
While details vary between species, members of this genus are fairly uniform in terms of general life history (Dechambre and Lachaume, 2001). Females deposit eggs in burrows dug into mulch, decaying vegetation, manure-rich soils, or soft, rotten wood. Standing, dead palms may be used as breeding sites, as well as rotten plant matter caught in the petioles of living palms. Larvae feed on organic debris within the nesting medium. Development of the pest species, Oryctes rhinoceros,takes 101–170 days from egg to adult emergence (Molet, 2013).
Severe. Though most of the 43 described species (Dechambre and Lachaume, 2001) of this genus are not considered pests, both Oryctes rhinoceros (Molet, 2013) and Oryctes monocerus (Allou et al., 2006) cause severe damage to palms and other host plants. Damage is caused when adults bore into the crowns of the host plant, burrowing as deep as 50 cm (19.7 in) into the hosts tissue (Molet, 2013). This results in destruction of unopened leaves and often the leaf midrib (Molet, 2013). After feeding on the juices produced by damaged host tissue, the beetle bores out of the host plant, often through the base of a frond (Molet, 2013). Plants, particularly young plants, can be killed either when the scarab damages the apical meristem or via secondary infection in the feeding burrow (Hinckley, 1973). In Palau, Gressitt (1953) attributed coconut mortality rates of 50% to damage caused by Oryctes rhinoceros. In Zanzibar, Mansfield-Aders (1920) reported that at some palm plantations, Oryctes monocerus killed over 50% of all young coconut palms.
Established. In Hawaii, Oryctes rhinoceros is currently established on Oahu where it was first detected in December 2013 on Pearl Harbor-Hickam Joint Base (Hawaii Department of Agriculture, 2014). Efforts are underway to eradicate the scarab and prevent its spread from Oahu. It is likely that this destructive beetle reached Hawaii by hitchhiking on military aircraft flying to Oahu from military bases on Guam, a known transportation pathway for several other invasive scarabs (Moore, 2012).
Established. In Guam, Oryctes rhinoceros has been established since approximately 2007, when specimens were found in the Tumon Bay area (Moore, 2007). The species has since spread to the remainder of the island.
The best known and probably most destructive member of the genus is the highly invasive Oryctes rhinoceros (the coconut rhinoceros beetle). Oryctes rhinoceros has been intercepted in quarantine on multiple occasions, with at least five U.S. interceptions known (Molet, 2013). Adults have been recorded on military equipment, air cargo, coconut "material", and potted plants (Molet, 2013; Bedford, 2015). It has also been reported that larvae are able to survive in floating logs out at sea (Molet, 2013). Any location where palms grow should be considered at risk for invasion by Oryctes species.
These large scarabs could be confused with the similarly sized and colored Japanese rhinoceros beetle (Trypoxylus dichotomus) and Xylotrupes species. Males of these scarabs can readily be separated by examining of the head horn (Oryctes with single, unbranched horn [ending in single point] versus Xylotrupes with the horn bifurcate [ending in two points] versus T. dichotomus with the horn doubly bifurcate [ending in four points]). Females are separated by examining the pronotum (Oryctes rhinoceros with a broad, sculpted depression versus Xylotrupes without a depression or fovea and T. dichotomus with a distinct, vertical fovea).