Pest an animal that causes harm to humans, their crops, livestock or possessions. Organisms that cause trouble, annoyance or discomfort are also considered as pests. However, whether an organism is a pest or not is a matter of opinion. The term 'pests' virtually covers all harmful insects and related terrestrial arthropods. In fact, the word is frequently restricted to these although some other invertebrate and vertebrate animals may be pestiferous.

Pests are classified in many different ways. Ordinarily they are considered as 'major' or 'minor' depending upon the extent of damage they cause in any particular ecosystem. They are also classified according to their mode of feeding, such as leaf feeders, sap suckers, stem and fruit borers, root feeders etc.

It has been suggested that an insect becomes an economic pest when it causes a yield loss of 5-10%. In any local pest complex, there are usually few major pests that are the most important. These cause most of the damage, and their control is urgently required. The most serious one of the major pests is often designated as the key pest. There are usually only one or two key pests in each agro-ecosystem. They usually have a high reproductive potential, and often a good survival mechanism. Generally some pests are found in abundance during a crop season (regular pests), while others may assume pest status occasionally in certain years (sporadic pests). Some pests normally cause negligible damage, but may become highly destructive if environmental conditions become favourable for them (potential pests).

Over 700 insect and mite pest species of different field crops, fruit trees, and stored products have been recorded from Bangladesh. Of these more than 200 species are considered as major. However, the list cannot be considered as a complete one. Pests of different crops and commodities have been separately described under appropriate entry tittles. [SM Humayun Kabir]

Pests of fabrics The important fabric pests recorded in Bangladesh include the dermestid beetles and clothes moths. Commonly known as black carpet beetle, Attagenus megatoma, carpet beetle, Anthrenus scrophulariae and A. fasciatus of family Dermestidae are often common in houses and may do serious damage to carpets, upholstery and clothings. The former is a grayish black and the latter is black and white patterned species. Most damage is done by their larvae.

The clothes moths (Lepidoptera, Tineidae) are small moths that attack clothes and woolen goods. The most common species is the webbing clothes moth, Tineola bisselliella. The adult is straw-coloured, without dark spots on the wing. The larvae feed on hair, fiber, wool, silk and similar materials and do not form cases. When full grown the larvae form a cocoon with the fragments of its food material fastened together with silk. Second in importance among clothes moths is the case-making clothes moth, Tinea pellionella which forms a case from silk and fragments of its food material. This case is tubular, open at each end, the larva feed, from within the case and pupates in it. The adult is brownish, with three dark spots on each front wing.
[Abdul Jabber Howlader]

Pests of stored grain Arthropods or other animals that destroy or deteriorate the quality of stored grains and grain products. An extensive survey of insects and mites associated with foods and seeds in storage has not yet been conducted in Bangladesh. Alam (1971) listed 29 species of insect pests attacking stored grain products of this country. His study, however, cannot be considered as complete.

Today, losses from storage pests cannot be measured only by the amount of food or seeds destroyed by insects. The mere presence of insect fragments in food is objectionable to most consumers. Thus economic losses may result from insect contamination, although actual losses of food materials due to insect feeding may be negligible.

Of the 29 orders into which insects are grouped, representatives of only nine have been recorded in association with stored products in Bangladesh, and even among these many occur accidentally. Many insects such as silver fish, fire brat, cockroaches, crickets, earwigs, and psocids are regularly found in dwelling houses, especially those that have stored grain. But these are not considered as pests. Strictly speaking, stored product insects belong to five orders of which the Coleoptera and Lepidoptera are the most important. Of the other three orders, the Hymenoptera are most numerous, while the Diptera and Hemiptera are of minor importance. Representatives of these three orders are not pests as such, but are either predatory or parasitic on other pests. At least four species of cockroaches occur in Bangladesh and they attack almost any kind of stored food.

Table 1 A list of insects and mites found in stored grain and grain products in Bangladesh with the host range

It is estimated that about 600 species of insects belonging to many different families are associated with stored products in various parts of the world. However, not all of them are pests. Bangladesh, one of the major rice and pulse-growing countries of the world, with its warm and humid climate possesses more than its share of stored product insect pests. Food commodities are imported to this country almost throughout the year from different countries of the world. Inevitably, new pests along with the imported grains get chance to enter Bangladesh all the time. Unlike in developed countries, grain is stored here in various ways, often unscientifically, and little attention is paid towards sanitation and contamination of pests. As a rule, grain stored in large quantities remain better than the same amount of grain stored in smaller lots. Large scientific granaries and warehouses are scarce in this country. In rural areas grain is still stored according to traditional indigenous methods and the same store or godown is used year after year without being properly cleaned. As a result, stores become quickly infested. Of all insect types, the coleopterans are most numerous as to the number of species and individuals followed by the lepidopterans. Of the coleopteran species, 2 are weevils and 7 are tenebrionids. Sitophilus zeamais seems to be a new comer to Bangladesh. Since its occurrence had not been reported from this part of the world previously. In 1976, only three lots of wheat samples collected from the CSD godown, Tejagon contained this species. Although its origins could not be confirmed, it is assumed that it came from North America (Kabir et al, 1989).

The tenebrionids are secondary pests but are quite obnoxious. They are common in broken and damaged grains and in ata, suji, maida (flour) and similar ground cereals. Dermestes maculatus is primarily a pest of dried fish. On the other hand, the khapra beetle, Trogoderma granarium, is quite common in granaries. Commonly known as pulse beetles or pea weevils, the members of the family Bruchidae are very notorious as pests of most of the pulses grown in Bangladesh. Callosobruchus chinensis and C. analis have a wide range of hosts but Bruchus pisorum infests only the pea.

Several species of hymenopteran parasitoids are associated with stored grains. Often they occur in abundance. Although they are parasitic in habit and constitute an important agent for natural control of many of the grain pests, their presence is as obnoxious to traders and consumers as the presence of insect pests.

Acarus siro is perhaps the best known of all the acarine pests of grains and flour in Bangladesh. They can build up enormous population during summer months. The other species occasionally found in association with A. siro is Glycyphagus destructor. [SM Humayun Kabir]

Bibliography MZ Alam, Pests of stored grains and other stored products and their control. Agricultural Information Service. Bangladesh Agricultural Research Institute. Dacca, 1971; SMH Kabir el al, Insects and mites associated with stored grain and grain products in Bangladesh. J. Asiat. Soc. Bangladesh, Sci. 15: 123-128, 1989.

Pests of leather Among the various pests, the members of the family Dermestidae of order Coleoptera are most important pests of leather. They are commonly known as skin beetles. They are mostly scavengers and feed on variety of animal products, including leather, furs, skins etc. Most damage is done by their larvae. Adult dermestids are small, 2-12 mm in length, oval or elongate-oval, convex beetles with short, clubbed antennae. The body is usually hairy or covered with scales. Dermestes vulpinus and D. lardarius are two common species that are encountered in Bangladesh. [Abdul Jabber Howlader]

Vertebrate pest Back-boned animal, which causes significant damage to crops, crop products, and other commodities. Among the various vertebrate pests rodents are by far the most important. Some birds, a few lagomorphs, and several species of wild mammals often cause economic injury and may become pestiferous.

Table 2 List of important rodent species and other potential vertebrate pests in Bangladesh

About two dozens species of rodents under 4 families occur in Bangladesh. Rodent damage is estimated to reduce the yield of wheat from 8 to12%, deepwater rice about 4.0% and pineapple from 6 to 9%. Rodents also cause damage to roads and highways, irrigation canals, residential houses, and other structures.

Among the rats the lesser bandicoot rat, greater bandicoot rat, roof rat, house mouse, and short-tailed mole rat are principal rodent pests of agricultural crops and houses in Bangladesh.

About 30 species of bats under 8 families of the order Chiroptera are known to occur in Bangladesh. Frugivorous bats cause extensive damage to banana, guava plantation, mango, litchi, and other fruits. In buildings, bats may become a nuisance by their squeaking, scratching, scrambling and crawling in attics and walls.

Wild boars and elephants often cause considerable damage to standing crops while passing through the crop fields, they may even eat the plants or grains prior to or at harvest. [Santosh Kumar Sarker]

Pest control any measure deliberately initiated by man to prevent, reduce or eliminate the harm caused by pest animals. In fact, any action that kills, or prevents the increase or distribution of pest organisms is considered as pest control. Although some control measures are effected in nature by natural factors including predatory, parasitic or disease organisms, several applied measures are commonly practiced to control insect or other pests.

Chemical control Reduction of pest population or prevention of pest damage by the use of chemicals to poison them or repel them from specified areas. Pesticides have been used commercially in the country from as early as 1951. At present, about 11,000 m tons of pesticides are used annually. These include insecticides, acaricides, fungicides, herbicides, nematicides, rodenticides, etc. About 245 insecticides have been registered officially. It has been estimated that around 10% of farmers in Bangladesh currently use pesticides.

Insecticides are seldom used in full concentration but are formulated in ways to dilute them and to make them easier to apply. The most common formulations are dusts, granules, insecticide-fertiliser mixtures, wettable powders, solutions, emulsifiable concentrates, aerosols, and fumigants. Since most farmers in Bangladesh are poor and illiterate, they know little about the hazards of pesticides; they always want quick and easy remedies. Since pesticides have the advantages of being easily available in the market, effective in curative action, adaptable in most situations, and flexible in meeting the changing agronomic and ecological conditions, use of chemicals in controlling pests is still the most common method adopted by Bangladeshi farmers. Pesticides are regularly used to control rice, jute, cotton, sugarcane, vegetables, and mustard pests.

Cultural control Reduction of insect pest population by the utilization of common agricultural practices; this involves the best cropping practices known for a given crop that may incidentally check possible insect populations from developing to the pest levels. Deep and thorough ploughing is a sanitation measure, which often results in burial of insects, making it impossible for them to escape. Another method of sanitation measure undertaken is removal and burning of weeds and crop remnants which harbour insects. Certain kinds of crop rotations may aid in the control of insect pests. Careful choice of crops and planting them adjacent to each other help reduce insect damage. Small scale planting of a susceptible or preferred crop is carried out near a major crop to act as a "trap". Change in planting time or harvesting time is used to keep infesting stage of a pest separate from the susceptible stage of the host. In addition, some other practices used in Bangladesh for insect pest control are choice of good seeds, improved varieties, proper seed-bed preparation, proper fertilizing, and soil conservation practices.

Mechanical control Reduction of insect pest population by using special mechanical devices rather than normal farm practices, a method based on the "catch and kill" and "uproot and burn" principle. In Bangladesh, the most important means are hand picking of egg masses, larval nests, and of weak fliers among young and adults. Hand nets and bags and inverted umbrellas are also used for collecting flying and migratory insects. Some household pests and fruit pests are controlled by means of beating and hooking. Cotton bugs and some insects of bushy shrubs can be collected by shaking and killed. Planting trap crops, use of light and suction traps, and burning of crop residues are also common practices. Moreover, mechanical exclusions like window screens, screen doors, mosquito nets, sticky bands on trees, shrouding young trees with cheesecloth, and paper collars around single plants also prevent insect infestation.

Legal control Control of insect pests through the enactment of legislation that enforces control measures or imposes regulations such as quarantines to prevent the introduction or spread of insect pests. It also operates to establish tolerance for poisonous residues on food, to regulate the sale of insecticides in such a manner as to protect the purchaser against fraud, to authorize and support extermination campaigns, and to provide facilities for investigations needed to establish control practices. In Bangladesh, there are 12 quarantine check-posts and these are situated at Zia international airport; Chittagong airport; Osmany airport in Sylhet; Chittagong and Mongla seaports; Narayanganj riverport; and in the following land borders: Benapole (Jessore); Burimari (Lalmonirhat); Tamabil (Sylhet); Darshana (Chuadanga); Hili (Dinajpur) and Sona Masjid (Chapai Nawabganj). Plant import regulations are reviewed constantly and revised according to the latest international scientific information available on all aspects of pests and diseases. [Monawar Ahmad and Masum Ahmad]

Biological control The use of parasites, parasitoids, predators, and pathogenic microorganisms by man for the suppression of insect pests populations. This method of pest control has several advantages over many other types of controls since it is relatively safe, permanent, and economical. One minor disadvantage is that it may take a long time to implement a biological control programme because of the research and the initial efforts involved in setting it up. However, the safety of this method is outstanding. Since many natural enemies are host-specific or restricted to a few closely related species, it is unlikely that nontarget species will be affected.

The potentiality of a successful natural enemy is one that has a high searching ability; a high reproductive rate; a high degree of host specificity; good synchronization with the host; and a high degree of adaptability to a wide range of ecoclimatic conditions.

It is estimated that about 613 species of natural enemies are associated with the arthropod pests of plant crops in Bangladesh. Of these, hymenopterous parasitoids predominate, followed by coccinellid predators. On the whole, parasitoids are dominated by chalcidoids, followed by ichneumonids, pteromalids, and tachinids.

Except for field surveys and lists, most of these species have not been throughly studied with respect to their potentials as biological control agents. Many studies of consumption rates by coccinellids of aphids have been undertaken. Field studies of their effectiveness as regulators of aphid populations are scanty. In 1993, Okuma et al prepared an illustrated monograph on rice field spiders of Bangladesh in collaboration with researchers of IPSA, BRRI, and Kyushu University, Japan.

Virtually no detailed work has been conducted in Bangladesh on pathogenic microorganisms that could be used to suppress insect pests. However, field tests with Bacillus thuringiensis as microbial insecticide for the control of rice ear-cutting and swarming caterpillars have come up with promising results. [Md. Zinnatul Alam]

Radiation control Suppression of harmful organisms through application of ionizing radiation. When applied at a certain dose levels radiation cause, deleterious effects on insect pests. When managed properly this effect could be used in pest management. Bangladesh has approved 12 food items for irradiation preservation. The other areas of radiation uses in pest control are phytosanitary activities, and animal and plant health inspection services in international trade. In particular, irradiation facilitates interstate and international shipment of fruits and vegetables, and other food items through eradication of pest or pathogen contaminations. Bangladesh takes such measures before the shipment of shrimps and prawns. The third area of potential radiation use is to control pest insects through sterile male technique, which has been successfully applied against several insect pests of economic importance including screw worm flies, fruit flies, tsetse flies, and the codling moth, cotton boll worm, and onion fly. [Reza Mohammad Shahjahan]

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