Insect Pests of Stored Grain and Their Management

The losses caused by the storage pests which include, insects, fungi, weeds, rodents and abiotic factors is to the tune of 10% (FAO, 1978)

Storage insect pests are categorized into two types:

1. Primary storage pests: Primary storage pests are those insects that damage sound grains or Primary storage grain insects pests have the ability to attack whole, unbroken grains. The eggs are laid outside the grain, before the larvae mature inside the grain and then chew their way out.

Primary storage pests are categorized into two type, Internal and External feeders/borers.

Internal Feeders/Borers:

External Feeders/Borers:

1. Secondary storage pests: Secondary storage pests generally feed on grain that is damaged or is going out of condition or damage broken or already damaged grains or Secondary storage pests attack only damaged grain, dust and milled products. Secondary storage insect pests feed on broken grain and any powder products left as a result of the broken grain.

Important points to be remembered:

• Khapra beetle is native to India.

• Pulse beetle prefers whole pulse not split pulse.

• Use fumigants like ethylene dibromide (EDB), ethylene dichloride carbon tetra chloride

(EDCT), aluminium phosphide (ALP) to control stored produce pests effectively.

• Granary weevil (Sitophilus granarius, the Wheat weevil).

• Crops can be completely destroyed or even partially damaged affecting the quality of the crop and the ability to germinate new ones, by decreasing the protein content and removing the seeds from the grains.

• Flat grain beetle is shortest insect in stored grain pests.

• Gaseous quinones released to the medium produces a readily identifiable acid odour in heavy infestations of - Red flour beetle: Tribolium castaneum

• Caryedon serratus is longest insect in stored grain pests.

• Name a storage pest on arecanut, coffee and cocoa - Arecanut beetle: Araecerus fasciculatus

• Caryedon serratus is a major stored grain pests of groundnut.

• Long headed flour beetle: Latheticus oryzae resembles – Tribolium castaneum

• Caterpillars of Angoumois grain moth produce large quantities of silk webbing.

• Sweet potato weevil and Potato tuber moth infestation is observed both in field and storage.

• Sitophilus oryzae, Sitotroga cerealella, Caryedon serratus, Tamarind beetle and Callosobruchus sp. Infestation starts from the field itself and carried to the godowns.

• A storage grain mixed with Malathion WP.

• For the long term safe storage of seeds the moisture content of the seed should be 7-8%.

• Chlorpyrifos methyl (Reldan) is effective against stored grain pests Khapra beetle, Rust Red flour beetle and Sitophilus oryzae but except stored grain pest Rhyzopertha dominica.

• Stored grain pest which is more sensitive /susceptible to spinosad is Rhyzopertha dominica.

• Potato tuber moth controlled by egg/larval parasitoid Chelonomus blackburni.

• The first case of insecticide resistance in India in stored grain pest was Tribolium castaneum.

• Chlorpyrifos methyl (Reldan), Cyfluthrin (Tempo) and Pirimiphos methyl (Actellic) insecticides used for the management of stored grain pests.

• Pusa bin is used for the control of Trogoderma.

• One Aluminium Phosphide tablet (three grams) release one gram of Phosphine gas.

• Hidden infestation can be detected by Staining method, Ninhydrin method and KOH method.

• The dropping are spindle shaped in Roof rat.

• Value depreciation of a product owing to the present of insects or other foreign matter is known as Dockage.

• Infestation of most of the insect pests can be avoided if the moisture content is below 9 % except Khapra beetle insect.

• Impact machine which are used to kill insects in stored products are called as Entoletors.

• The composition of Aluminium Phosphide is Aluminium Phosphide (56%), Aluminium Carbamate (41%) and Paraffin wax (3%).

• The concentration of the gas per unit volume x time of exposure is called as Critical value (CT Value).

• Phosphine gas that is liberated when Aluminium Phosphide tablet reacts with moisture.

• Recommended dose of Phosphine fumigation is 3 gram Aluminium Phosphide tablet/tonne with an exposure period of 7 days.

• Zinc phosphide and Barium carbonate is a acute rodenticides (Single dose and quick acting)

• Warfarin and Bromodiolone is a Chronic rodenticides (Multiple dose and slow acting)

• Bromodiolone is Multiple dose poision, slow acting poision and anticoagulant.

• Methyle Bromide, Sulfuryl floride (Profume) and Phosphine fumigant used for the management of stored grain pests.

• Grain Psocids (Liposcelis spp) are scavengers and most common in slightly damp stores/materials.

• Storage pest that feeds on animal products (dried blood & dried insect) is known as Khapra Beetle.

• Khapra beetle hibernates in cracks and crevices during grub stage.

• Khapra beetle adult does not consume the grains but only grub is damaging stage.

• Saw toothed grain beetle grub pupate within a silken cocoon.

• Saw toothed grain beetle hide in cracks and crevices of building and machinery.

• The Saw toothed grain beetle name has been derived due to characteristics teeth running down the pro thorax(Six tooth like projections on each side of thorax)

• Insect pests attacking seeds in storage lower the percentage of seeds which germinate.

• Many grain pests preferentially eat out grain embryos, thereby reducing the protein content of feed grain.

• Pulse beetle hibernation in grub stage.

• Adult of pulse beetle does not feed seed.

• Angoumois grain moth besides reducing the grain weight, impart an unpleasant smell and taste to the cereals.

• The storage pest that is commonly found in broken cereals and their milled products like atta, maida and suji is known as Rust Red Flour Beetle

• Flate grain beetle pupation take place in a cocoon.

• Lesser grain borer is most serious in hot and dry conditions.

• Atta formation is the main symptoms of Lesser grain borer damage by which infestation in the godown can be easily detected.

• Unlike the Lesser grain borer (A strong flyer and may rapidly migrate from infested grain to begin new infestations elsewhere), the rice weevil may occasionally fly.

• Rice weevil pupate inside the grain.

• Indian meal moth female lay eggs near the grain surface.

• Red Squill and Strychnine is a rodenticide of botanical origin.

• Khatti is an underground storage structure.

Insecticides approved by Registration Committee (RC) for control of stored grain pests under the Insecticides Act, 1968.

• Aluminium Phosphide

• Deltamthrin 2.5% WP

• Methyle Bromide

• Ethylene Dichloride + Carbon Tetrachloride (3:1)

• Methyle Bromide (98%) + Chloropicrin 2 % w/w.

Phosphine fumigation 

Larval and adult stage are more susceptible than egg and pupa.

It has little reaction with more commodities,

It does not effect the germination and milling qualities.

Methyle Bromide fumigation 

All insect stages are effective and requires less exposure period.

It is widely used for plant quarantine and food processing facilities.

It destroys stratospheric ozone layer.

Anticoagulant 

They are safer than acute rodenticides because they are less toxic to the non target species.

Quick knock down effect.

Cost of operation is cheap.

Disadvantage of Zinc phosphide baiting is 

Necessity of prebaiting

Induce bait shyness

Toxix to non target species.

Management of stored insects:

It is broadly classified into two categories, preventive and curative methods.

1. Preventive or Prophylactic method:

2. Clean godown before storing the harvested crop.

3. Seal and plaster the cracks and crevices in godowns that are hiding places for most of the storage insect pests including rodents.

4. Machineries should be properly cleaned before being used for processing and threshing.

5. To avoid entry of birds, rats and squirrels, fix wire meshes to windows, ventilation etc.

6. Drying of seeds under natural sunlight exposes that larva or eggs on grains and kill them.

7. Storing the seeds under good ventilation godowns and warehouses to prevent build up of moisture which is favorable to insects for multiplication. For example rice can be safely stored at 13 % moisture content whereas wheat, sorghum and maize may be stored safely at 13.5 % moisture content at a temperature of 27^oC as given in below table

* Value are upper limit values.

1. Spraying of insecticides on godown walls , floor, alleyways and surface of the grain bags with Malathion 50 % ECV(1:100 dilution rate) and Deltamethrin 2.5 % WP (40 grams in 1 liter of water) @ 3 liters emulsion on 100 m² surface area.

2. Curative/Physical methods:

3. Additional methods of insect control include smoking, sun-drying, admixing of dusts or ashes or mixing of dusts or ashes with seeds.

4. Use of insecticides like Malathion, Dichlorvas, and Deltamethrin as prophylactic spray on godown walls, storage surface etc.

5. Use of fumigants viz., Aluminium phosphide sold under trade name Celphose(3tablets/tonne of grain) that is properly used to fumigate the grains. One Aluminium phosphide tablet is of 3 gram weight which release one gram of phosphine gas.

6. Methyle bromide (98%) is also used for fumigation against whole cereals, millets and pulses at 24g/m³ in air tight cover with 6-8 hrs exposure period and waiting period of 24 hrs.The residues should not exceed 25 ppm and similarity it is approved for use of milled products (flour) and also for dry fruits, nuts, spices and oil seeds @ 24-32 g/m³ with 12-24 hrs exposure and waiting period of 72 hrs.

7. Mixing of seeds only with Malathion WP.

8. Once grains are infested , even controlled atmosphere technique can be used to kill storage pests where the gases viz., CO₂ concentration is increased in the close spaces which close the spiracles of insects and kills the insects through asphyxiation(Physical control).

9. The minimum exposure period of fumigation in godowns is 5-7 days except for empty godowns and sheds it is 3 days.

• Fumigation dose based on Stored quantity: Fumigation with Aluminium phosphide 56% for stored whole cereals, seed grains, millets, pulses, dry fruits, nut, spices & oilseeds, milled products, deoiled cakes rice bran flour, grain animal & poultry feed, split pulses (Dal) and other processed foods etc @ 3 tablet/ ton.

• Fumigation dose based on Space occupied: Fumigation with Aluminium phosphide 56% for stored whole cereals, seed grains, millets, pulses, dry fruits, nut, spices & oilseeds is 150g/100m³

• whereas milled products, deoiled cakes rice bran flour, grain animal & poultry feed, split pulses (Dal) and other processed foods is 225g/100m³

• Fumigation dose for Empty Godowns & Sheds: Fumigation with Aluminium phosphide 56% for for Empty Godowns & Sheds is 14 tablets/1000 Cu ft. or 150g/100m³

• Insecticide resistance

Insect populations of many species have evolved resistance to insecticides as a result of the widespread use of these chemicals in control. In some cases, insects which have only been exposed to one insecticide develop resistance to other, related compounds.

It takes many years and millions of dollars to develop and test new compounds. Therefore it is important that insecticide resistance is prevented from spreading. This may be achieved by appropriate use of pesticides and by farm hygiene. This consists of careful cleaning of all machinery and buildings used for storing and transporting grain right from the header to the port terminal.

About Authors:

Dr. Hadi Husain Khan: Research Associate, ICAR-DRMR-APART, Dhubri -783324 (Assam), India.

Dr. Mohd. Monobrullah: Principal Scientist, Division of Crop Research, ICAR-RCER, Patna- 800014 (Bihar), India.

Dr. Anjani Kumar: Director, ICAR-ATARI, Zone – IV, Patna- 801506 (Bihar), India.

Dr. Akhtar Ali Khan: Professor, Division of Entomology, SKUAST, Kashmir, Shalimar, Srinagar - 190025 (J&K), India.