|Geographical Distribution of Banana weevil in Africa (red marked)
The banana weevil (C. sordidus) is known from virtually all banana-growing countries of the world, including the New World, Afrotropics, Oriental and Australasian regions.
|Banana corm damaged by banana weevil. Note tunnelling by weevil grubs and rotting of corm.
|© A. M. Varela, icipe
Grubs feed making irregular tunnels in the corm and rootstock. Tunnels are roughly circular and can reach up to about 8 mm in diameter. The corm can be riddle with tunnels, which promotes fungal infection and decay reducing it to a black mass of rotten tissue. Injury to the corm can interfere with root initiation and sap flow in the plant, as a result the leaves turn yellow, wither and die prematurely. In particular young suckers show symptoms of wilting and die, but older plants are retarded in their growth. Heavily infested plants produce small bunches, and are easily blown over by the wind. Spent stems, cut or standing are attacked rapidly.
Damage is worst in neglected plants. In fertile soils and with good crop husbandry it is seldom serious. Banana weevil numbers are often low in newly planted fields. Population build-up is slow and weevil problems are most often encountered in ratoon crops. The banana weevil damage is more serious in low altitude areas that in highland areas as a result of the influence of temperature. Weevils are usually not a problem beyond 1500 m above sea level (Karubaga and Kimaru, 1999; Gold and Messiaen, 2000).
Banana weevil is an important pest of banana and plantain (Musa spp.), and ensete (Ensete spp.). Weevil problems appear to be most severe in plantains, highland cooking bananas and ensete. The weevil has contributed to the decline and disappearance of highland cooking banana in parts of East Africa. Weevil pest status in other groups of bananas is variable. In commercial Cavendish plantations where the banana weevil has been reported to be relatively unimportant (Gold and Messiaen, 2000).
Infestation by the banana weevil begins at the base of the outermost leaf-sheath and in injured tissues at the lower part of the pseudostem. Initially the young grubs make several longitudinal tunnels in the surface tissue until they are able to penetrate to adjacent inner leaf-sheaths; they then bore into the pseudostem base and rhizome/corm, but also into the base of suckers and into roots. Larval tunnels may run for the entire length of fallen pseudostems. Infested plants have dull yellow green and floppy foliage. Young infested suckers often wither and fail to develop. Plants are easily blown down by mild to strong winds.
Affected plant stages
Flowering stage, fruiting stage, seedling stage and vegetative growing stage.
Affected plant parts
Roots and stems.
Roots: internal feeding
Stems: internal feeding