PESTS OF STORED GRAINS Worldwide losses in stored products caused by insects have been estimated to be between 5 and 10%. Stored-product insects cause serious postharvest losses, estimated to be from 9% in developed countries to 20% or more in developing countries. They also contribute to contamination of food products by presence of live insects, insect products such as chemical excretions, dead insects and insect body fragments and accumulation of chemical insecticide residues in food, making the food unfit for human consumption. 1. Pulse Beetle, Callosobruchus chinensis L.: (Coleoptera: Bruchidae) Distribution: The beetle’s natural ranges are in the tropics and subtropics of Asia. Host Range: C. chinensis is a common and major pest of stored legumes. Preferred hosts are Vigna radiata (mung bean), Pisum sativum (pea), Vigna unguiculata (cowpea), Cajanus cajan (pigeon pea), Vigna angularis (adzuki bean) and Lens culinaris (lentil). Nature of Damage: The larvae chew tunnels through the bean until it is ready to pupate. Larvae feed and develop inside the seed and when adults emerge they leave a neat circular exit hole. Heavy infestation causes the commodity to heat. This results in loss of quality and mould growth. 2. Lesser Grain Borer, Rhyzopertha dominica Fabricius: (Coleoptera: Bostrichidae) Distribution and Status: It is found in India, Algeria, Greece, the USA, New South Wales (Australia), Japan and China. Host Range: It is found on wheat, rice, maize, sorghum, barley, lentils, army biscuits, ship biscuits, stored and dried potatoes, corn flour, beans, pumpkin seeds, tamarind seeds and millets. Nature of Damage: The lesser grain borer is characterized as both an internal and external feeder and is a serious pest of both whole kernel stored grain and cereal products. The adults and grubs bore into the grains feed and reduce them to mere shells with many irregular holes. Heavy infestation with lesser grain borers can be identified by a sweetish, musty odour in the storage. This odour is a result of the male-produced aggregation pheromone. It is a strong flyer and may rapidly migrate from infested grain to begin new infestations elsewhere. 3. Rice Weevil, Sitophilus oryzae L.: (Coleoptera: Curculionidae) Distribution: It is distributed worldwide and is found practically throughout India. Host Range: It is found in rice, sorghum, wheat, barley and maize. Nature of Damage: Both the adults and the grubs cause damage. The developing larva lives and feeds inside the grain, causing irregular holes of 1.5 mm diameter on grains of rice, sorghum, wheat, barley and maize before harvest and in storage. The weevils destroy more than what they eat. 4. Granary Weevil, Sitophilus granarius: (Coleoptera: Curculionidae) Distribution: It is distributed worldwide. Host Range: The hosts for the granary weevil include the maize, barley, wheat, groundnut, oats, chickpea, sunflower, rice, millets, rye, sorghum, triticale, broad bean and a variety of dried stored products. Nature of Damage: Adults feed on whole seeds or flour. Larvae develop inside seeds or pieces of seed or cereal products large enough to house larvae but do not develop in flour unless it has been compacted. Weevils can achieve almost complete destruction at high densities. Feeding contributes to heating and infested grain is often damp due to moisture added by the insects’ metabolic processes. 5. Rust-Red Flour Beetle, Tribolium castaneum Herbst: (Coleoptera: Tenebrionidae) Distribution: It is cosmopolitan in distribution. Host Range: It is the most common pest of wheat flour. It also causes serious damage upon dried fruits, pulses and prepared cereal foods, such as cornflake, pasta, biscuit, beans, nuts, etc. Nature of Damage: The greatest damage is caused during the hot and humid monsoon season. The larvae are always found hidden in the food. The adults, however, are active creatures, but mostly found concealed in flour. Adults construct tunnels as they move through flour and other granular food products. In severe infestation, the flour turns grayish and mouldy and has a pungent, disagreeable odour, making it unfit for human consumption. Both larvae and adults feed on grain dust and broken grain, but not the undamaged whole grains, and spend entire life cycle outside the grain kernels. This insect causes substantial losses during storage because of its high reproductive potential. 6. Confused Flour Beetle, Tribolium confusum: (Coleoptera: Tenebrionidae) Distribution: It is cosmopolitan in distribution. Host Range: It is the most common pest of wheat flour. It also causes serious damage upon dried fruits, pulses and prepared cereal foods, such as cornflake, pasta, biscuit, beans, nuts, etc. Nature of Damage: The greatest damage is caused during the hot and humid monsoon season. The larvae are always found hidden in the food. The adults, however, are active creatures, but mostly found concealed in flour. Adults construct tunnels as they move through flour and other granular food products. In severe infestation, the flour turns grayish and mouldy and has a pungent, disagreeable odour, making it unfit for human consumption. Both larvae and adults feed on grain dust and broken grain, but not the undamaged whole grains, and spend entire life cycle outside the grain kernels. This insect causes substantial losses during storage because of its high reproductive potential. 7. Khapra Beetle, Trogoderma granarium Everts: (Coleoptera: Dermestidae) Distribution: It is one of the world’s most feared stored-product pests; and has been described as one of the 100 worst invasive species worldwide. Host Range: It is an external feeder. Khapra beetle attacks any dried plant or animal matter. It prefers grain and cereal products, mainly wheat, barley, oats, rye, maize, rice, flour, malt and noodles. It can also feed on animal products, such as dead mice, dried blood and dried insects Nature of Damage: Larvae feed on a wide variety of stored products and dried foods. They eat the grain near the embryo or at any other weak point and from there proceed inwards. They usually confine themselves to the upper 50 cm layer of grains in a heap or to the periphery in a sack of grains. They can reduce the grain to a mere frass. The hairs shed by larvae may cause asthma and skin or gastric problems. 8. Rice Moth, Corcyra cephalonica Stainton: (Lepidoptera: Pyralidae) Distribution: Corcyra cephalonica (Stainton) is economically an important stored grain pest in Asia, Africa, North America and Europe. It is cosmopolitan in distribution. It occurs in Asia, Africa, North America and Europe. Host Range: It infests broken grains of rice, wheat, sorghum, maize, gram, groundnut, cotton seed, milled products, coffee, cocoa beans and millets. Nature of Damage: This pest is internal feeder. Caterpillars cause the damage by webbing together grains and forming lump and feed from inside. Larvae before pupation wander about and leave a lot of webbing in the grains, causing excessive lumping, which reduces marketing quality of the grains. Ultimately, a characteristic foul odour develops and the grains are rendered unfit for human consumption. The caterpillars produce a large amount of frass (in which they hide) compared to other stored food moths. This material can attract other stored food pests, such as flour beetles (Tribolium spp.). 9. Indian Flour Moth, Ephestia spp.: (Lepidoptera: Pyralidae) Ephestia is comprised of many species, viz. Ephestia elutella, Ephestia cautella, Ephestia mistralella Milliere, Ephestia kuehniella Zeller and Ephestia unicolorella, distributed across the globe. Distribution: It has worldwide distribution, occurring both in the tropical and temperate climates of the world. Host Range: It causes quantitative and qualitative economic damage in stored cocoa beans and other stored products like cocoa beans, dried fruits, nuts, grains, etc.. Some species are important pests of seeds and cereals. Best known among these are probably the cacao moth (E. elutella) and the Mediterranean flour moth (E. kuehniella). Nature of Damage: The moths in the grain result in reduced grain weight and dockage because of contamination by faecal material and webbing. The silken webs produced by the caterpillars may even interfere with normal operations of machinery such as flour sieves. 10. Angoumois Grain Moth, Sitotroga cerealella Oliver: (Lepidoptera: Gelechiidae) Distribution: The Angoumois grain moth is considered a major pest of stored agricultural products worldwide. Host Range: It is commonly called Angoumois grain moth because it was first time reported from Angoumois province of France. It can be found infesting a variety of grains, e.g. paddy, wheat, maize, sorghum, barley, oats, etc., and food materials. They attack all cereal grains and are most often found in corn and wheat. It is the only storage pest that attacks standing grains in the field. Nature of Damage: The newly hatched caterpillar bores directly into the grain and typically remains inside the grain for both larval and pupal development. The larvae of this pest tunnel inside the kernels, cause substantial damage and render the grain more susceptible to secondary insect pests. Adults are unable to penetrate grain and, therefore, only infest surface layers of grain. It is a pest of whole cereal grains, which only infests surface layers of bulk stored grains. The damage is at its maximum during the monsoon. Only the larvae cause damage by feeding on the grain kernels before harvest and also in store. The larva bores into grain and feeds on its contents. Exit holes of 1 mm diameter with or without a trap door are seen on the affected cereal grains. As it grows, it extends the hole, which partly gets filled with pellets of excreta. It imparts unhealthy appearance and smell. In a heap of grain, the upper layers are most severely affected. MANAGEMENT OF STORED GRAIN INSECTS 1. Preventive Measures: (a) Brush the cracks, crevices and corners to remove all debris in the godown. Clean and maintain the threshing floor/yard free from insect infection. (b) Clean the machines like harvester and thresher before their use.