Oryctes rhinoceros (coconut rhinoceros beetle)

O. rhinoceros is included in the Global Invasive Species Database (ISSG, 2009).

O. rhinoceros eggs are yellowish-white, measuring 3 mm in diameter and laid inside rotting vegetative matter. Initially oval in shape, they begin to swell about a week after laying and hatch within 11-13 days (Wood, 1968a).

The larval stages are usually yellowish-white in colour and may grow to about 60-100 mm long, or more (Wood, 1968a; Ooi, 1988). The maximum head capsule width is about 10.6-11.4 mm. The cranium is medium to dark brown, with numerous round pits, many of which bear minute setae. Thoracic spiracles are 1.85-2.23 mm long, 1.25-1.53 mm wide. Respiratory plate with a maximum of 40-80 or more small, round to oval holes along any diameter. Thoracic spiracles larger than abdominal spiracles; first abdominal spiracle somewhat smaller than succeeding spiracles (for detailed information, see Bedford, 1974 ). The larval stages may look similar to other species within the scarabeid family (e.g. Xylotrupes gideon, Scapanes australis, Trichogomphus fairmairei, Oryctes centaurus and Oryctoderus sp.). A key to differentiate the larval stages of these species has been provided by Bedford (1974) . The presence of the organ of Herold on the ventral surface of the ninth abdominal segment indicates the male sex (Hurpin, 1953 ; Elliott, 1964). A description has been provided for third-instar larva of  Chalcosoma atlas  (Bedford, 1976a) which co-exists in Malaysia with  O. rhinoceros  and may be confused with it, while in the African region  O. monoceros  is widespread, for which a description of the larva is available (Bedford, 1979). Lucanid and cetoniine beetles, which often shared the same breeding sites, may also be confused with the early instars of O. rhinoceros (Wood, 1968a) and a key for separating some of these types of larvae has been provided for Papua New Guinea (Beaudoin-Ollivier et al., 1998, 2000).

The prepupa is somewhat similar in appearance to the larval stage, except that it is smaller than the final larval instar. Shrivelled in appearance, it shakes its body actively when disturbed.

The O. rhinoceros pupa is yellowish-brown in colour and measures up to 50 mm in length. It is segmented on the dorsal surface. The length of the horn-shaped protuberances on the anterior may indicate the sex of the adult.

Stout-looking adults, dark brown to black, shiny, 35-50 mm long and 20-23 mm wide, with a prominent horn on head (Wood, 1968a; Bedford, 1974). The males having a relatively longer horn than the female. The males can be differentiated more accurately by having a rounded, shiny terminal abdominal segment while the female has a relatively hairier 'tail' (Wood, 1968a). The strikingly similar but larger species of scarabeid, Oryctes gnu (= trituberculatus ) may be confused with O. rhinoceros (Wood, 1968a). The difference is the three tubercles on the thoracic ridge for O. gnu, instead of two in O. rhinoceros . A key to Oryctes species is given by Endrödi (1985) .

O. rhinoceros is endemic to the coconut-growing regions of South and South-East Asia from Pakistan to the Philippines (CIE, 1967). It was accidentally introduced into parts of Papua New Guinea in the Bismarck Archipelago (New Britain, New Ireland, Manus Island); Western and American Samoas, Tonga, Fiji, Wallis Island, Micronesia, Mauritius and the Cocos Islands (Bedford, 1974, 1980). It has recently been found in Guam and Saipan (Moore, 2007) and Hawaii (Hawaii Department of Agriculture, 2014).

McKenna and Shroff (1911) reported that the pest first appeared in the extreme south of Myanmar, probably from Malaysia in 1895, and worked its way through to the north over the next 15 years. It was also introduced to Upolu island in Western Samoa in 1909 via potted rubber seedlings from Sri Lanka (Jepson, 1912).

O. rhinoceros  is thought to have spread throughout the Pacific by increased sea traffic during World War II. The pest has also been found in air cargo and may be transported to new areas in decaying organic materials such as compost and sawdust, and in nursery pot plants. The larvae may also be transported to new areas in floating logs.

Primarily found attacking coconut and oil palm, O. rhinoceros has also occasionally been recorded on banana (Sharma and Gupta, 1988), sugarcane, papaya, sisal and pineapple ( Khoo et al., 1991 ). In Mauritius, ornamentals such as the royal palm (Roystonea regia), the latanier palm (Livistona chinensis), the talipot palm ( Corypha umbraculifera) and the raphia palm (Raphia ruffia) are attacked (Bedford, 1980).

O. rhinoceros adults feed in the crown region of both coconut and oil palm. On oil palms they bore through petiole bases into the central unopened leaves. This causes tissue maceration and the presence of a fibrous frass inside and at the entrance to the feeding hole is an indication of its activity within (Catley, 1969). A single attack may be followed by others on the same palm (Barlow and Chew, 1970; Young, 1975). These attacks subsequently produce fronds which have wedge-shaped gaps or the characteristic V-shaped cuts to fronds (Wood, 1968a; Sadakathulla and Ramachandran, 1990).

The strikingly similar but larger species of scarabeid, Oryctes gnu (= trituberculatus ) may be confused with the adult O. rhinoceros (Wood, 1968a). The difference is the three tubercles on the thoracic ridge for O. gnu, instead of two in O. rhinoceros . The larvae of Xylotrupes gideon are more hairy than those of O. rhinoceros . The head capsule at each larval stage is also smaller (Wood, 1968a). Aegus chelifer larvae are relatively hairless, relatively more translucent, with an orange head and a longitudinal anal slit (Wood, 1968a). Coelodera diardi larvae appear to be very similar to the second-instar O. rhinoceros larvae but are less curved. When placed on a slippery surface they swiftly move away on their backs. See Description for keys to larvae and adults, also Bedford (1976a) for a description of the Chalcosoma atlas larva from Malaysia, and Bedford (1979) for the larva of O. monoceros  from the Seychelles.

O. rhinoceros eggs are laid in rotting palm materials including trunks, tree stumps, compost heaps, dung hills, sawdust or garbage dumps. The eggs hatch after 8-12 days and the entire larval stage is spent inside the breeding medium. Development of the larva takes 80-200 days: first instar takes 10-21 days, second instar takes 12-21 days and third instar takes 60-125 days. The beetle then enters the prepupal stage of about 8-13 days, subsequently pupating within a pupal chamber made from the food substrate. The pupal stage lasts 17-30 days. Adults may live up to 6 months or more (Bedford, 1980; Khoo et al., 1991).

Bedford (1976c, 1980) reviewed the life-cycle of O. rhinoceros and noted a wide range in the duration of the third-instar larvae (60-165 days) compared to the other stages. This may be caused by differences in climatic and nutritional conditions of different habitats. Dry climate or low nutritional conditions often delayed larval development of O. rhinoceros, which can be extended to as long as 14 months, giving rise to smaller-sized adults (Catley, 1969). Catley (1969) also demonstrated that with ample food supply, the duration of the third-instar larvae is within 3-4 months. With superior and improved larval diet combined with suitable temperatures, the duration of the larval stages can be shortened from 6 to 5 months (Schipper, 1976). Similarly, Wood (1968a) demonstrated that the larvae required about 5-7 months to mature in oil palm log tissue, while a shorter maturity period of 4-5 months was observed in a habitat mixture of cowdung and sawdust. Conditions suitable for larval development are temperature (27-29°C) and RH 85-95% (Bedford, 1980).

The adult beetles feed by boring into the growing point or meristem of coconut palms and this is the primary cause of crop damage leading to loss of yield and death in in coconut palms of all ages. Similar attacks stunt growth or may kill young oil palms. The larvae feed on dead wood; dead palm logs and stumps and the tops of dead standing coconut poles are a primary breeding site.

The entomopathogenic virus Oryctes rhinoceros nudivirus (OrNV), which was originally discovered in Malaysia (Huger, 1966), attacks both the larval and adult stages of O. rhinoceros . It has since been introduced into Fiji (Bedford, 1976d, 1985, 2013), the Maldives and other islands in the South Pacific to control O. rhinoceros in coconut (Marschall, 1970 ; Marschall and Ioane, 1982 ; Young and Longworth, 1981 ; Zelazny et al., 1992).

Oryctes larvae also succumb to attack by the green entomopathogenic fungus, Metarhizium anisopliae (Sundara Babu et al., 1983). However, tests have shown that O. rhinoceros larvae are susceptible only to strains isolated from the same species (Fargues, 1976). Latch (1976) tested 34 isolates of Beauveria bassiana and B. tenella on O. rhinoceros larvae and found 17 isolates causing lesions similar to those by M. anisopliae .

Bacterial pathogens which have the potential to control larval stages of Oryctes were identified as Acinetobacter calcoaceticus (Kannan et al., 1980), Pseudomonas alcaligenes (Gopal and Gupta, 2002),  Bacillus thuringiensis and B. popilliae (Sundara Babu et al., 1971; Norman et al., 2005) and Protista flagellates Monocercomonoides oryctesae and M. qadrii (Krishnamurthy and Sultana, 1977).

A list of predators and parasitoids for O. rhinoceros tested in the Pacific area has been compiled by Swan (1974), and includes Coleoptera (Elateridae, Histeridae and Carabidae), Hemiptera (Reduviidae), centipedes and vertebrates (rats, mice, shrews, squirrels, lemurs, monkeys and pigs). Wood (1968a) also reported the barn owl ( Tyto alba javanica ) as a predator of the beetles. Other natural enemies affecting O. rhinoceros include hymenopteran (Scoliidae) and dipteran (Tachinidae) parasitoids.

On oil palms, O. rhinoceros bores into the base of the cluster of unopened leaves (spears), causing V- or wedge-shaped cuts in the unfolded fronds. Spears may collapse or emerged fronds may break off along the petiole or midrib (Wood, 1968a). In young palms where the spears are narrower and penetration may occur lower down, the effects of damage can be much more severe than in older palms (Wood, 1968a). The young palms affected by the beetle damage are believed to have a delayed immaturity period (Liau and Ahmad, 1991). Thus, early oil palm yields could be considerably reduced after a prolonged and serious rhinoceros beetle attack. Although Wood et al. (1973) suggested that the damage to the immature palms results in relatively small crop losses, field experiments conducted by Liau and Ahmad (1991) revealed an average of 25% yield loss over the first 2 years of production. This was possibly caused by the reduction in the canopy size of more than 15% for moderately serious to higher damage levels (Samsudin et al., 1993). In India, the infestation in oil palm was more prevalent in mature plantations (10-15 year old) compared to immature or younger plantings (Dhileepan, 1988).

Similarly, on coconut the reduction in leaf area of the palms influences nut production (Zelazny, 1979a) but the attack was more towards the tall, mature trees, from about 5 years of age onwards (Bedford, 1976c). Serious attacks on coconut may be observed in areas adjacent to a breeding site with a high beetle population, especially in the coastal region of Peninsular Malaysia. Zelazny (1979a) reported an average of 10% of fronds damaged by cuts resulted in a 3% reduction of the leaf area and a 4-5% loss of nut production; similarly 30% of fronds damaged resulted in a 7% reduction of the leaf area and 13% nut yield reduction, i.e. loss.

On both oil palms and coconuts, O. rhinoceros bores through the petiole bases into the central unopened leaves. This causes tissue maceration and the presence of a fibrous frass inside the feeding hole is an indication of its activity within (Catley, 1969). The adults may be forced out by 'winkling' with a hooked barbed wire into the feeding hole. Larval, pupal as well as adult population may be detected and inspected by digging into or breaking open its possible breeding sites its possible breeding grounds.