SEED SCIENCE & TECHNOLOGY - SEED STORAGE INSECTS.pdf
- 1. SEED SCIENCE &TECHNOLOGY SEED STORAGE INSECTS Dr. K. Vanangamudi Formerly Dean (Agriculture), AC & RI, Coimbatore Dean, Adhiparashakthi Agricultural College, Kalavai Professor & Head (Seed Science & Technology) Tamil Nadu Agricultural University, Coimbatore. 1. Storage losses due to insects Damage due to % of loss Pests 36-43 Rodents 35-72 Fungus 4-8 Birds 12-34 Moisture 9-21 Others 1-7 Weight loss: For grains or grain legumes in the tropics, a loss in the range of 10-30 per cent might be expected over a full storage season. Loss in quality/market value: Infested seed is contaminated with insect debris and has increased dust content. Seed are holed and often discoloured, which fetch low price. Promotion of mould development: In humid conditions, without adequate ventilation, mould development and caking can spread rapidly, causing severe losses. Reduced germination in seed material: Damage to the embryo of the seed will usually prevent germination. Some storage pests prefer to attack the embryo.
- 2. 2. Important storage insects and pests of cereals and pulses Order Family Common name Scientific name Commodities infested Coleoptera Curulionidae Rice weevil Sitophilus oryzea Cereals Bostrichidae Borer beetle Rhyzopertha dominica Cereals, pulses and dried roots Dermestidae Khapra or cabinet beetle Trogoderma granarium Everts Cereals and cereal by- products, oilseed cakes and meals, finished feed, pulses Bruchidae Pulse or seed beetle, bean weevil Callosobruchus maculatus Pulses Tenebrionidae Rust red flour beetle Tribolium castaneum Cereals and cereal by- products, oilseed cakes and meals, finished feed Long headed flour beetle Latheticus oryzae Cereals Silvanidae Saw toothed grain beetle Oryzaephilus surinamensis Cereals and cereal by- products, oilseed cakes and meals, finished feed Lepidoptera Gelenchiidae Grain moth Sitotroga cerealella Cereals Rice moth Corcyra cephalonica Cereals Fig or almond moth Ephestia cantella Cereals Meal worm moth Plodia interpunetella Cereals 3. Identification of storage pests 3.1. Rice weevil - Sitophilus spp. – oryzae Distinguishable from all other common storage pests by the long beak characteristics of all the weevils, 2.5 to 4 mm long, dark brown, sometimes with four lighter spots on the wing cases (Fig. 1).
- 3. Fig.1. Rice weevil Infects maize, rice, sorghum and wheat (Fig. 1). The most important primary pests of cereals in the humid tropics, attacks undamaged grain, often infests before harvest. The larvae develop within the grain, leaving a characteristic round hole on emergence. 3.2. Angoumois grain moth - Sitotroga cerealella A small cream or fawn coloured moth sometimes with a small black spot on the forewing, the wings are very narrow and fringed with long bristles, the sharply pointed tip of the hind wing is characteristic (Fig. 2). Fig.2. Angoumois grain moth Infects sorghum, maize (Fig. 2), wheat and rice. Damage may be very serious in maize stored on the cob damage is more limited with shelled grain, as the moths do not penetrate more than a few centimeters from the surface. The developing larvae cause all damage, as the adults do not. 3.3. Lesser grain borer - Rhyzopertha dominica A small, almost cylindrical beetle, with the head "tucked" under the thorax so that it is invisible from above, the thorax has a prominent pattern of tubercles. Infects sorghum, maize and other cereals (Fig. 3), cassava.
- 4. They are capable of attacking previously undamaged seed where they can cause serious damage. Fig.3. Lesser grain borer 3.4. Larger grain borer - Prostephanus truncatus Very similar but slightly larger than the lesser grain borer. Weight losses caused by this pest are 3 to 5 times higher than those caused by the normally occurring pest (Fig. 4). Fig.4. Larger grain borer 3.5. Bruchids - Callosobruchus maculatus Rather stout beetles, active, with long legs and antennae; antennae not "clubbed" wing areas often mottled, spotted or otherwise marked; last segment of abdomen just visible beyond wing cases (Fig. 5). Infestation often commences in the field before harvest; larvae develop hidden within the bean. Eat only embryo by making round holes.
- 5. Fig.5. Bruchids 3.6. Indian meal moth: Plodia interpunctella Larva is damaging the grain. Larvae grayish white. Adult wing expends 2 mm, lustrous brown, yellowish/whitish band across the basal half (Fig. 6). Fig.6. Indian meal moth 3.7. Rice moth: Corcyra cephalonica Corcyra is uniformly dark grey-brown, dirty creamy white larvae with dominant broad yellow head (Fig. 7). Various species on cereals, milled cereal products, groundnuts, dried fruit. Can be major primary pests, and important on flour and other products, larvae, which are free-living caterpillars, spin silk as they move. Fig.7. Rice moth 3.8. Red flour beetle- Tribolium castaneum Elongated, reddish-brown beetles, active (Fig. 8). It attacks cereals (especially after damage by primary pests), groundnut, milled cereal products.
- 6. Can attack intact grain via the embryo, but infestation is usually more serious on damaged or milled products, where they can be major pests. Fig.8. Red flour beetle 3.9. Khapra beetle - Trogoderma granarium Dark brown, marbled with lighter bands, very finely hairy, 3 mm long, larvae with lone conspicuous bristles. Easily confused with other dermestids, if an infestation is suspected, identification by an expert should be sought (Fig. 9). It attacks groundnuts, cereals, grain legumes. Major pest in drier areas, important partly because larvae can enter a resistant resting phase, difficult to eradicate. Fig.9. Khapra beetle 3.10. Saw-tooth grain beetles: Oryzaephilus surinamensis Active, dark-brown beetle, about 4 mm long, markedly elongated and flattened in shape; recognizable by the six prominent teeth on each edge of the thorax (Fig. 10). It attacks cereals (especially rice), cereal products, oil-seeds. Secondary pests; can be particularly important on milled products. Fig.10. Saw-tooth grain beetles
- 7. 3.11. Flat grain beetle – Laemophloeus minutus Very small (1 to 2 mm), flattened, red-brown in colour (Fig. 11). It attacks cereals, cereal products, cowpeas and cocoa. Can become very abundant, especially in flour or damaged grain. Fig.11. Flat grain beetle 3.12. Granary weevil: Sitophilus granarius Damaging stage-larvae and adult. Marks of identification – larger than rice weevil, uniformly shiny black/reddish brown elytra larger oval pits on the thorax (pronotum) without functioning wing (Fig. 12). Fig.12. Granary weevil 3.13. Confused flour beetle- (Tribolium confusum) Damaging stage - larvae and adult. Marks of identification: Similar to red flour beetle, but larger in size, antennae gradually enlarged towards the tip (Fig. 13). Eyes smaller then red flour beetle.
- 8. Fig.13. Confused flour beetle 3.14. Long headed flour beetle - (Latheticus oryzae) Damaging stage- larvae. Marks of identification- adult 3 mm, slender, flattened and pale brown. Larvae yellowish white, dark coloured head and leg (Fig. 14). Fig.14. Long headed flour beetle 4. Management of storage pests 4.1. Sanitation It is crucially important to reduce the initial pest population and prevent development of any insect pests in the crop seeds. Before bringing a new crop seed into store, the following steps are necessary. Remove infested material. Do not mix new seed with old, old material that should be thoroughly fumigated. Clean the storage structure Brush away all traces of spilled seed, dust, etc. Remove dust from handling equipment and machinery Disinfect sacks and baskets by sunning or chemical treatment Take control measures early to prevent infestation of crops maturing in the field.
- 9. 4.2. Seed store sanitation Storage room should be clean and disinfected with residual sprays of insecticide such as malathion 50 EC (one part in 25 parts of water) @ 5 litres per 100 m2 area or fenitrothion 50 EC (one part in 100 parts of water). 4.3. Fumigation Seed should be inspected at fortnightly interval. In the event of detection of any insect infestation. Seed must be fumigated under air tight conditions with any one of the following fumigants: Aluminium phosphide: 2-3 tablets; of 3 g each per tonne of material with an exposure period of 3-5 days or 1 tablet per m3 space. Ethylene dibromide (EDB): 32 g per m3 space with an exposure period of 5-7 days. Aluminium phosphide is the safest fumigant. Maximum of 3 fumigation may be given at an interval of 40-60 days. It does not impair seed viability, if seed moisture and temperature does not exceed 12% and 35°C, respectively. After fumigation, seed store should be aerated and cleaned thoroughly. To prevent reinfestation. surface treatment with malathion 50 EC or fenitrothion 50 EC (one part in 100 parts of water) @ 4-5 litre per m2 area or malathion dust 5% @ 3-4 kg per 100 m2 should be given. The treatment may be given at an interval of 2-4 weeks depending upon severity of pest occurrence. 5. Methods to assess the damage 5.1. Visual inspection Seeds are spread in an enamel tray and inspected visually with naked eye or under illumination depending upon the size of seed. The material is closely scrutinized for the presence of any living or dead insect /mite and their stages, exuviae, and damaged seeds. The insect can be detected based on the symptoms of damage caused as morphology detailed below.
- 10. 5.2. Symptoms of damage caused by some storage pests Symptoms Crop Pest Brown/damaged seed Maize, rice, sorghum, wheat, oat, barley Red flour, saw toothed and flat grain beetle Circular holes Pulses, wheat, rice, maize, sorghum and grasses Pulse beetle, rice weevil, angumois moth Irregular holes Spices Lesser grain borer, cigarette beetle Seeds reduced to husk Wheat Khapra beetle Webbing Maize, rice, wheat Indian meal moth Musty odor and dust All seeds Mites 5.3. X- ray radiography Seeds are spread in a single layer on a transparent plate and are exposed to x- ray @ 22 KV, 3 MA for 10 seconds at a distance of 30 cm. On the radiography, healthy and infested seeds are clearly distinguishable. 5.4. Transparency test Seeds are treated with lactophenol on a boiling water bath for 10-20 minutes (different from crop to crop). With the reaction of lactophenol seed coat becomes transparent. Each and every seed is observed with the help of magnifier to confirm the presence of insect within the seed. This method is useful for the crops with small seed size. Lactophenol should be used with proper care.