A. Sivapragasam and Loke Wai Hong*
Identification of P. reichei which infests the coconut palms of Malaysia is clarified and its history and biology are elaborated. Continuous hot weather and the consequential low natural enemy populations are cited as factors that lead to outbreaks. Control measures (cultural practices, insecticides and natural enemies) are reviewed.
Numerous insect pests infest the coconut palm, Cocos nucifera L. at all stages of its growth in Malaysia. Approximately 184 insects have been recorded, excluding those infesting copra, only a few are key pests of perennial importance. These include the rhinoceros beetle, Oryctes rhinoceros and the red stripe weevil, Rhynchophorus vulneratus. Some chrysomelids (hispids) are sporadic but important pests, such as the two-coloured coconut leaf beetle (B. longissima), Plesispa reichei (Chapuis) and the coconut leafminer, Promecotheca cumingii (Baly) (syn. P. nuciferae). Of the latter, P. cumingii is a true leafminer whereas P. reichei feeds on the surface of the leaves. This paper provides an informational review on Plesispa spp. with specific reference to P. reichei.
The first probable reference to P. reichei in Malaysia is in a report of the Director of Agriculture for 1912 that cites collection from a coconut palm in Johore. Subsequently, it was reported as a minor pest in other states – Selangor and Perak. The first major outbreak occurred in 1916 in an estate where 385 000 larvae and adults were collected from 500 acres of 12-month-old palms. Baker (1918) and later Corbett (1932) indicated that P. reichei had been erroneously called Bronthispa (sic) froggatti in Malayan entomological literature (see Richards 1917). Another species of Plesispa was collected by Corbett in 1921 near Malacca from the nipah palm (Nipah fruticans) and was named P. nipae Maulik (commonly known as the nipah hispid). The damage caused by this insect to the nipah palm was similar to that caused by P. reichei (commonly known as the coconut hispid) on coconut palms. Further, the two species of Plesispa had a similar characteristic as their larvae fed on the surface of the leaves. However, the eggs of P.nipae are laid in groups whilst those of the coconut hispid are laid singly. Both species differed in colour; the prothorax of P. reichei is yellowish while that of P. nipae is reddish (Corbett 1932).
Recently, there has been some confusion about the identification of Plesispa and Brontispa (see Figure 1a-c) especially when a recent report from a meeting† illustrated B. longissima as shown in Figure 1c. It is hoped the following descriptions of the species will help to clarify correct identification.
Figure 1a. Plesispa reichei. The adult female, about 9.5 - 10 mm long, is flat with a dark brown head and antennae. The thorax is yellowish brown and the elytra are black (Yunus and Balasubramaniam 1970).
Figure 1b. Brontispa longissima (syn. Brontispa froggatti). Adult beetles are elongated, dorsoventrally flattened and 8 - 12 mm long. Some specimens have brown or black elytra, or have a spindle-shaped black marking on the elytral suture.
Figure 1c. Plesispa (or Brontispa?)
Generally, hispines have a limited distribution (Howard et al. 2001). The CABI pest distribution data suggest that Plesispa reichei is present in Indonesia, Malaysia, the Philippines, Singapore, Thailand and Samoa.
As early as 1923, Corbett (1923) noted P. reichei as a pest of seedlings in nurseries and young plants in the field up to two or three years of age. Both the larval and adult stages feed between the closely appressed leaflets of the young unfolded fronds (and thus are well concealed) consuming the upper and lower surfaces of the tender partially folded leaves (Figure 2). The young leaves appear dessicated (Plate 2). Growth of seedling plants is often seriously retarded and if the attack is severe and of long duration, the plants may die. It is a major pest of coconut palm nurseries in the Philippines, Indonesia and Thailand (Howard et al. 2001). Field observations by the authors on infestations by adults and larvae indicated that the Yellow Dwarf variety was the least infested and the Malayan Talls were highly susceptible among the Malaysian varieties assessed. A major outbreak of P. reichei was reported in Singapore in early 1988 on coconut, Roystonea regia and R.. oleracea (Choo-Toh 1999). The pest situation was significantly bad enough to warrant a major intervention programme. Choo-Toh (1999) reported 12 species of palms attacked in Singapore of which C. nucifera, Veitchia merrilli (Becc.) H.E. Moore and R. oleracea were the most severely damaged.
Figure 2. Damage by Plesispa on coconut
The adult female, which is about 10 mm in length, lays an average of 112 reddish-brown eggs during its life span and they hatch within 7 - 10 days (Figure 3a). Yunus and Balasubramaniam (1970) reported 5 - 10 days in Malaysia. The eggs are laid singly about 7 - 10 days after copulation. The flat and yellowish larva has 11 pairs of lateral projections (Figure 3b). It undergoes four instars and the larval period varies from 30 - 38 days with a mean of 33 days. In Malaysia, Yunus and Balasubramaniam (1970) reported 22 - 38 days. The flat and yellowish pupa is positioned with its ventral surface to the leaf and is capable of movement. The pupal period varies from6 - 11 days with a mean of seven days. There are variations in the literature on the duration of the life cycle. Generally, it ranges from 43 - 59 days. Corbett (1932) indicated 40 - 64 days. The elytra of the adult beetle, on emergence from the pupa are creamy white, but soon acquire their characteristic black colour with a brownish-orange head and thorax. The adult lives for about nine months. The male is about 8.5 mm in length. Adult beetles shun light and prefer dark places. According to Corbett (1923), the sex ratio is generally biased towards females.
Figure 3a. Plesispa eggs
Plate 3b. Plesispa larvae
There is scant information on this pest possibly due to its sporadic occurrence. Prolonged drought as observed in Miri Sarawak (Megir Gumbek 1999), continuous hot weather and the consequential low natural enemy populations are factors that lead to outbreaks (Choo-Toh 1999).
Cultural practices: Control in nurseries includes hand-collection during low infestations. Besides cultural practices, such as cutting and burning of infested leaves, insecticides have been used.
Insecticides: During severe infestations, insecticide applications are common. According to Megir Gumbek (1999) trunk injection with monocrotophos was effective in coconuts. The efficacy of foliar sprays of insecticides was highly dependent on the height of palms (Choo-Toh 1999), such sprays were generally more effective in shorter palms. Foliar spraying of dimethoate with other contact chemicals has been recommended for spraying palms shorter than 2.5 m (Choo-Toh 1999). Resistance of the pest to dimethoate was suggested when the pest re-appeared even after seven sprays. Besides foliar spraying, soil drenching of systemic insecticides, trunk injection with dimethoate and methamidophos and crown and soil application of carbofuran were also attempted. Crown application with carbofuran sachets produced the most convincing results, even for tall palms (Choo-Toh 1999). Of the insecticides tested, the mixture of chlopyrifos and cypermethrin (NurelleR) was effective against field populations of P. reichei infesting young coconut germplasm.
Natural enemies: Despite their cryptic habits, the insect is attacked by a number of natural enemies that include many species of ants, dermapterans and parasitic hymenopterans. Endemic natural enemies tended to keep the populations of P. reichei in check under natural conditions. The natural enemies recorded for the species include two species of encyrtids, Ooencyrtus podontieae and Ooencyrtus sp. and a trichogrammatid, Haeckeliona brontispae which attacks the eggs. The parasitoid, Tetrastichus brontispae parasitizes the larvae and the pupae of P. reichei and P. nipae as well as B. longissima. According to CABI records, natural enemies include Hispidophila brontispae, Ooencyrtus corbetti and Tetrastichus plesispae. In Malaysia, Corbett (1923) reported an egg parasite (O. podontiae). Parasites collected from both P. reichei and P. nipa, were able to manage the problem of the Mariana coconut beetle, Brontispa mariana Spaeth. in Saipan (Lange 1950).
Baker, C.F. 1918. Identity of a coconut hispid. Gdns’ Bull. Straits Settl., 2: 3.
Choo-Toh, G.T. 1999. An outbreak of Plesispa reichei Chapuis on palms in Singapore. In Sivapragasam et al. eds. Proceedings of the 5th international conference on plant protection in the tropics, 15 - 18 March 1999, pp. 64 - 69.Kuala Lumpur, Malaysia.
Corbett, G.H. 1923. Preliminary note on the two-colored coconut leaf beetle (Plesispa reichei). Chap. Malay. Agric. J., 11: 64 - 69.
Corbett, G.H. 1932. Insects of coconuts in Malaya. General Series No. 10. Department of Agriculture, Straits Settlements and Federated Malay States.
Howard, F.W., Moore, D., Giblin-Davis, R.M. & Abad, R.G. 2001. Insects on palms. CABI Publishing.
Lange, W.H. Jr. 1950. The biology of the Mariana coconut beetle, Brontispa mariana Spaeth. on Saipan, and the introduction of parasites from Malaya and Java for its control. Proc. Hawaii Ent. Soc., 14: 143 - 162.
Megir Gumbek. 1999. Outbreak of coconut leaf miner, Promecotheca nuciferae in Sarawak. In Sivapragasam et al., eds. Proceedings of the 5th international conference on plant protection in the tropics, 15 - 18 March 1999, pp. 390 - 393. Kuala Lumpur, Malaysia.
Richards, P.B. 1917. The diseases and pests of the coconut palm. Agric. Bull. F.M.S., 5: 327 - 337.
Yunus, A. & Balasubramaniam, A. 1970. Major crop pests in Peninsular Malaysia. Bulletin No. 138, Agriculture Division, Ministry of Agriculture, p. 65.
* Respectively, Rice and Industrial Crops Center, MARDI, G.P.O. Box 12301, 50774, Kuala Lumpur, Malaysia and CAB International SEA Regional Center, P.O. Box 210, 43409, UPM Serdang, Selangor, Malaysia
† Expert consultation on coconut beetle outbreak in APPPC member countries; FAO RAP Publication 2004/29