|Crop Knowledge Master|
Cosmopolites sordidus (Germar)
|Banana Root Borer|
Ronald F.L. Mau, Extension Entomologist
Jayma L. Martin Kessing, Educational Specialist
Department of Entomology
Updated by: J.M. Diez April 2007
The banana root borer is a major pest of banana and Manilla hemp (abaca). It infests and seriously damages all varieties of banana and plants belonging to the genus Musa. Substantial losses can result if this pest is not controlled. Although it will attack all parts of banana suckers (keikis) and established plants, it prefers decaying banana corm material. Spent stems (cut or left standing), residual corms left after the stem has been cut, underground stubs of corm tissue left after de-suckering, uprooted suckers or stems, and any corm tissues that are large enough to dry slowly are good targets for banana root borer attack (Hely et al., 1982).
Dispersal within a banana field occurs when adult weevils walk from plant to plant or when infested plants containing eggs and larvae are moved. Dispersal between distant fields undoubtedly is caused by the transportation of infested planting material.
The weevil is native to Malaysia and Indonesia but is found in nearly all banana-growing areas of the world. Some of the areas where it occurs are Australia, Central and South America, Florida, India, Mexico, some Pacific islands, Southeast Asia and the West Indies. It was first reported in Hawaii on the island of Oahu in 1981 and has spread to Hawaii, Kauai, Maui and Molokai.
Injury is caused by grubs (larvae), which tunnel through the corms. Tunnels are circular in cross section, become wider as the grub grows (approximately 1/3 inch in diameter) and are filled with dark-colored debris (Franzmann, 1972). Extensive feeding damage by grubs results in root destruction, slowed plant growth, reduced fruit production, and, sometimes, toppled plants. The tunneling by the grubs makes the corms susceptible to invasion by secondary decay organisms. Reduced production and growth of suckers (keikis) occurs when parent plants are heavily damaged. Affected sucker plants can be recognized by their dull, yellowish-green withered leaves. Relatively little damage is caused by adults feeding on plant tissues (Franzmann, 1972).
The life cycle (egg to adult) of the banana root borer requires 30 to 40 days.
The white, sausage-shaped eggs are about 1/12 inch (2 mm) long. They are deposited singly in cavities chewed by the adult females in the corm or pseudostem at ground level or between leaf sheath scars on the crown of the banana corm. They are difficult to detect in the field because they are often hidden by congealed sap produced by the banana plant after the cavity is created (Franzmann, 1972). Egg laying also occurs in the corm of fallen plants (Waterhouse and Norris, 1987). Eggs hatch in 5 to 7 days.
The stout, creamy white, legless grubs have reddish-brown heads and fleshy white bodies. When mature they are about 1/2 inch (12 mm) long. The grubs are normally found in the pseudostems up to 2 feet above the ground. Development is completed in 15 to 20 days.
Grubs pupate within chambers that are usually close to the surface of the corms. Pupae are white and about 1/2 inch (12 mm) long. No cocoon is formed (Froggatt, 1925). Pupal development is completed in about 8 days.
The black, hard-shelled weevil is about 1/2 inch (12 mm) long with a long snout (Franzmann, 1972). Newly emerged weevils are reddish brown before turning black (Kranz et al., 1977). Female lay an average of 1 egg a day during their life span. Adults are reported to live for as long as 2 years. They are capable of surviving for extended periods without food.
The nocturnal adults rarely fly although they have well-developed wings and movement is mostly by walking. They hide under debris or in the soil around banana plants during the day and are active at night. Adults move sluggishly and feign death if they are disturbed (Hely ,et. al., 1982).
Adults are attracted to freshly cut pseudostems (trunks) and corms, and population estimates can easily be made using traps consisting of these plant parts. Two trapping methods are used in Central and South America banana populations.
The split-log trap uses fresh banana pseudostems cut into 1- to 1 1/2-foot lengths. The pseudostem logs are then split lengthwise through the center, and the halves are placed with the split surfaces on the soil at a number of locations in the field.
The stump trap uses recently harvested plants. Trunks are cut about a foot from ground level. A piece of the remaining trunk is removed by making a second cut at a 30- to 45-degree angle about 6 inches from the ground. The resulting piece of trunk is placed back on the stump. Adult weevils are attracted to the surface between the piece and the stump.
A minimum of three survey counts should be made at 2- to 3-day intervals to obtain reliable estimates. Adults should be removed each time. An average of 5 adults per trap is the action threshold for the split-log trap; an average of 15 to 20 adults is the threshold used with the stump trap. Insecticidal treatments are recommended when counts exceed the action threshold.
Only 15 predators of the banana root borer have been reported (Ostmark, 1974). There have been several attempts of biological control using predatory beetles throughout the Pacific, especially Plaesius javanus and Dactylosternus hydrophiloides, but they have been mostly disappointing (Ostmark, 1974; Waterhouse and Norris, 1987). Life history information on Plaesius javanus is reported by Weddell (1932). Although the predators are able to establish populations (usually after several attempts at introduction) their effectiveness as predators is not well known and suspected to be minimal (Waterhouse and Norris, 1987). Other factors contributing to the poor effectiveness of these predators are that most of the predators are not specific predators of the banana root borer and the banana root borer larvae and pupae are located in tunnels within the banana plant and protected from most predators (Ostmark, 1974). Consequently, large bio-control programs for the banana root borer have not been implemented. There have been no introductions of beneficial insects to Hawaii to control this pest.
The following integrated control program is recommended to minimize damage by the banana root borer.
1. Plant-clumps or mats should be cleaned of plant debris.
2. Harvested plants should be removed from the field weekly to eliminate hiding places for adults. Stumps should be removed and the corms cut into 4 to 8 pieces and allowed to dry. This practice prevents larval development in the harvested plants.
3. Transportation of planting material from infested fields to uninfested ones should be avoided to prevent rapid dispersal of this pest to uninfested areas.
4. If keikis from infested fields are to be replanted nearby, the outer leaf sheaths should be removed and the corms trimmed to remove eggs or young larvae that may be present. Keikis may be treated in hot water instead, using the established method for burrowing nematode disinfestation. However, these methods will only minimize the chance of planting an infested keiki.
5. Chemicals may be needed if the number of adults caught by trapping exceeds action thresholds.
For many years persistent insecticides such as dieldrin and aldrin were used in controlling this pest. Today, banana root weevils are reported to be resistant to these materials in several areas of the world, and other insecticides are now being used. Primicid, Furadan, Nemacur, Dasanit, and Lorsban are pesticides that have been reported to be effective. Primicid and Lorsban are not registered for use on banana in Hawaii. Of the remaining products, Furadan is though to be the most effective.
Home gardens. Diazinon is the only chemical that can be used to control this pest on banana in home gardens. It can provide adult control for short periods and may need to be applied at 3- to 4-week intervals until trap counts indicate that the pest has been controlled. Diazinon sprays should be applied to the bases of the plants and to the ground between them. In order for sprays to be effective, steps 1 and 2 given above must be followed.
Commercial Farms. Furadan can be used by commercial banana growers. It provides control for longer periods. The manufacturer recommends that applications be made at 4- to 6-month intervals. Furadan is highly toxic to humans, and its use is restricted to licensed applicators only.
There are no insecticides currently registered as of April 2007.
Franzmann, B. A. 1972. Banana Weevil Borer in North Queensland. Queensland Agricultural Journal. 319-321.
Froggatt, J. L. 1925. The Banana Weevil Borer. (Cosmopilites Sordidus Chev.). Queensland Agri. J. 24: 558-593.
Hely, P. C., D. G. Pasfield and J. G. Gellatley. 1982. Banana weevil borer Cosmopolites sordidus. pp. 174-175. In: Insect Pests of Fruit and Vegetables in NSW. Inkata Press; Melbourne, Sydney and London. 312 pages.
Kranz, J., H. Schmutterer and W. Koch. 1977. Cosmopolites sordidus Germ. pp. 406-409. In: Diseases, Pests and Weeds in Tropical Crops. Verlag Paul Parey, Berlin and Hamburg.
Mau, R. F. L. 1981. The Banana Root Borer, A New Pest. Hawaii Cooperative Extension Service Farm and Home Insect Pests Entomology Notes No. 11. University of Hawaii, College of Tropical Agriculture and Human Resources.
Mau, R. F. L. 1982. Banana Root Borer, Cosmopolites sordidus (Germar) (Coleoptera: Curculionidae). Horticulture Digest. 66: 3-5.
Ostmark, H. E. 1974. Economic Insect Pests of Bananas. Ann. Rev. Ent. 19: 161-176.
Waterhouse, D. F. and K. R. Norris. 1987. Chapter 20: Cosmopolites sordidus (Germar). pp. 152-158. In: Biological Control Pacific Prospects. Inkata Press, Melbourne. 454 pages.
Weddell, J. A. 1932. The Banana Weevil Borer. Brief Notes on Plaesius javanus Er., the Histerid Predator. Queensland Agri. J. 38: 24-29.