A weevil is any beetle from the Curculionoidea superfamily. They are usually small, less than 6 mm in length and herbivorous. There are over 60,000 species in several families, mostly in the family Curculionidae . There are more species in this family than in any other beetle group. Scientists estimate that there are over 1,000 species of Curculionidae in North America. Weevils are generally divided into two major divisions, the Orthoceri or primitive weevils, and the Gonatoceri or true weevils. Weevil species occur in a wide range of colors and body shapes. Many are slender or oval-shaped insects. Depending on the species, weevils range in size from about 3 mm to over 10 mm in length. They are usually dark-colored—brownish to black. Some have scales or shiny hairs covering part of their bodies. The most distinctive feature of weevils is the shape of their head. An adult weevil has an elongated head that forms a snout. The mouth is at the end of the snout. Some weevils have a snout that is as long as the body.
Most of the weevils are destructive to crops and are categorized as agricultural pests. They feed on crops as larvae as well as adults. Most weevils are found in fields, gardens or orchards. They can be very destructive, and their damage is often very expensive. For many years, one of the most destructive weevils was the cotton boll weevil. The black vine weevil, is found in many parts of the United States. It feeds on a variety of plants, including hemlocks and rhododendrons.
A few weevils attack stored grains and seeds. Weevils are often found in dry foods including nuts and seeds, cereal and grain products, such as pancake mix. In the domestic setting, they are most likely to be observed when a bag of flour is opened. Their presence is often indicated by the granules of the infested item sticking together in strings, as if caught in a cobweb. The most common stored product weevils are the rice weevil, the granary weevil, and the cowpea weevil. Sometimes plant-feeding weevils invade homes for shelter from the weather. Occasionally people accidentally bring seed-feeding weevils into the kitchen.
Banana weevil is the most important pest of banana plantations. 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. According to a study conducted by cirad banana plots are colonized from already infested neighboring plots or from reservoirs, such as semi-natural wild banana stands. Plot organization within an agricultural landscape thus plays an important role in the spread of weevils, as does the position of the various elements within plots – banana plants, harvest residues, cover crops, pheromone traps, etc. It is its larvae that damage banana plants, by boring galleries in the bulb, which prevent the plant from taking up sufficient nutrients and sometimes cause it to fall.
Substantial losses can result if this pest is not controlled. Although it will attack all parts of banana suckers 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. 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 injury is caused by grubs (larvae), which tunnel through the corms. Tunnels which are circular in cross section become wider as the grub grows and are filled with dark-colored debris. 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 occur 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.
The damage caused by the banana weevil is demonstrated by this article published recently in The Hindu:
NATIONAL » TAMIL NADU
NAGERCOIL, September 8, 2013
Updated: September 8, 2013 10:24 IST
Stem borer a nightmare for banana farmers
- KOLAPPAN
The entry of banana weevil, a common pest, in tribal areas across the Petchiparai dam has become a cause of concern for both farmers and officials of the horticulture department as these areas had once been totally free from the pest.
‘Nenthiran’ and red bananas planted in these areas have become its victims. “Commonly known as stem borer, the pest could wreak havoc on banana crop and contribute to drastic decline in banana cultivable area.” said Surendran Joseph, Assistant Director, Horticultural Department in Kanyakumari district, who identified the pests during a field visit.
Mr Joseph said when he received complaints of banana stems bending over and collapsing at Thatchamalai during the flowering stage, he was under the impression it could be due to some fungus attack.
“Even last year there was no incidence of this pest. But now I am surprised to find that it is the handiwork of the stem borer,” he said. Even though the problem was prevalent in Kanyakumari district, particularly in Vilavancode taluk, the borer could not make a foray into tribal areas all these years.
He felt the weevil, which could reach 10-16mm length with a hard-shelled and curved snout, could have invaded the area along with banana suckers brought from outside for planting.
The damage is caused by the grub (larva of the weevil), which makes tunnels as it feeds on the corm and root stock. The tunnels encourage fungal infection, ultimately reducing it into a black mass of rotten tissues. This hinders root initiation and sap flow to the plants.
“The infection will result in yellowing of leaves and withering; particularly, young suckers show symptoms of wilting. In older plants, growth is retarded. In case of severe infection, plants produce small bunches and are easily blown over by wind,” he explained.
Mr Joseph said the pest could be controlled through crop rotation, drip irrigation, selection of healthy planting material and keeping the garden clean from weeds and crop debris. “Uproot the infested plant, chop it into pieces and burn them. Removal of pseudo stem below the ground level,” he said, and advised farmers to avoid planting susceptible varieties such as robusta and red banana
He said if the planting material is suspected of being infested, the suckers should be trimmed on all sides so as to eradicate the presence of eggs and grubs.
The above incident strikes a chord close to home. India being a country majorly dominated by agriculture as a source of livelihood, the crops need to be protected from vicious insects like weevils and bedbugs.
Conventional pesticides used have numerous environmental consequences. The use of toxic pesticides means exposing our pristine soil to the evils of degeneration, degradation of soil quality, groundwater pollution, etc. A better way is to use non-conventional products. Unconventional products like Termirepel™ a product of C Tech Corporation are the best for this job. Termirepel™ can be best described as a non-toxic, non-hazardous termite aversive. It is effective against a multitude of other insects and pests like weevils, beetles, etc. It works on the mechanism of repellence and therefore does not kill the target as well as non-target species. Being non-toxic, it does not harm the soil and environment.