A. Insects

Insects in stored rice can be classified into four groups according to their feeding habits namely internal feeders, external feeders and scavengers.
1. Internal Feeders
These are insects whose larvae feed entirely within the kernels of the grain. These includes rice weevil, angoumois grain moth and lesser grain borer.
Rice Weevil (Sitophilos oryzae (Linnaeus)): Adults and larvae feed on a wide variety of grains. Female deposits a single egg in the grain by boring a hole inside. The egg stays in the grain until it becomes an adult thus making the grain completely damaged.
Angoumois Grain Moth (Sitatroga cerealella (Olivier)): Eggs are laid on or near grain. The white larvae bore into the kernels of the grain and feed on the inside. When mature, the larvae eat its way to the outer portion of the grain, leaving only a thin layer of the outer seed coat intact. Pupation takes place just under the seed coat. When the adult emerges from the grain, it pushes aside the thin layer of seed coat leaving a small trap door covering its exit point from the kernel. They infest only the surface layer of bulk-stored grain, adults are unable to penetrate deeply.
Lesser Grain Borer (Rhyzopertha dominica (Fabricus)): The eggs are laid in the grain mass and larvae may enter the kernels and develop within or, they may feed externally in the flour-like dust that accumulates from the feeding of the adults and their fellow larvae.
2. External Feeders
External feeders are insects that feed from the outside of the grain even though they may chew through the outer coat and devour the inside.
Cigarette or Tobacco Beetle (Lasioderma serricorne (Fabricius)): Feeds on books, flax tow, cottonseed meal, rice, ginger, pepper, dried fish, crude drugs, seeds, pyrethrum powder, and dried plants.
Flat Grain Beetle (Cryptolestes pusillus (Schonherr)): The female places her eggs loosely in the grain mass. The larvae and adults are able to penetrate the seed coat of the undamaged grain.
3. Scavengers
Scavengers feed on the grain only after the seed coat has been broken either mechanically or by some other insect.
Saw-toothed Grain Beetle (Oryzaephilus surinamensis (Linnaeus)): Eggs are usually laid, either singly or in small masses, in a crevice in the food supply but in items like flour, they are laid freely.
Pictures and main characteristics of the three main storage pests (sitophilus, tribolium, and ryzopertha):
Sitophilus oryzae
Common name: Rico weevilFamily: Curculionidae
Description:
size: 2.5 - 3.5 mm shape: more or less cylindrical colour: black-brown with four reddish spots on the elytra recognition: well defined snout: elbowed and clubbed antennae; circular punctures on the prothorax; can fly
Life history range of temperature: 17 - 34°C optimal temperature: 28°C range of rel. humidity: 45 - 100% optimal rel. humidity: 70% eggs laid: up to 150 separately deposited inside the grain life cycle: 35 days at optimum110 days at sub-optimal conditions
DamageAdults and legless larvae are primary pests of cereals, rice and dried cassava. Larvae spend their lives inside the grain.
Tribolium castaneum
Common name: Rust-red flour beetleFamily: Tenebrionidae
Description size: 3 - 4 mm shape: elongate body, more or less parallel sided colour: red brown - dark brown recognition: antennae are inserted under the sides of the head (frontal ridge) and form a three-segmented club; elytra with finely punctured lines
Distribution: throughout the tropics and the subtropics
Life history range of temperature: 22 - 40°C optimal temperature: 35°C range of rel. humidity: 1 - 90% optimal rel. humidity: 75% eggs laid: up to 500 life cycle: 20 days under optimum conditions
DamageLarvae and adults are secondary pests and attack cereals and cereal products, groundnuts, nuts, spices, coffee, cocoa, dried fruit and occasionally pulses. Infestation leads to persistent disagreeable odours of the products.
Rhyzopertha dominica
Common name: Lesser grain borerFamily: Bostrichidae
Description size: 2 - 3 mm shape: slim, cylindrical colour: red-brown to black-brown recognition: head concealed beneath prothorax (typical for the Bostrichidae); prothorax bears marginal rows of teeth; elytra with well defined rows of punctures
Distribution: mainly in tropical and sub-tropical regions
Life history range of temperature: 18 - 38°C optimal temperature: 34°C range of rel. humidity: 25 - 70% optimal rel. humidity: 60 - 70% eggs laid: 300 - 500 life cycle:20 - 84 days
Damage
Primary pest of cereal grains, other seeds, cereal products, dried cassava, etc. Damage is done by adults and larvae, which develop within the grain.
(source: Gwinner et al, Manual on the Prevention of Post-harvest Grain losses, GTZ, Escborn, 1996)
B. Rodents
Rodents are characterised by their teeth. They have a pair of incisor teeth in the upper and lower jaws. The incisors are curved inwards and have an extremely hard anterior coating. The softer inside layer is worn down much more rapidly than the hard, outer layer. This means that the teeth are continually kept sharp, enabling them to damage even materials such as masonry and electric cables. The incisors do not stop growing. This means that the animals are forced to gnaw steadily in order to wear them down.
The three most important rodent species are:
· Black rat or House rat (Rattus rattus)
· Norway rat or Common rat (Rattus norvegicus)
· House mouse (Mus musculus)
There are also a number of species which are of great importance in specific regions:
· Multi-mammate rat (Mastomys natalensis) in Africa and the Middle East;
· Bandicoot rat (Bandicota bengalensis) in Southern and South East Asia;
· Pacific rat (Rattus exulans) in South East Asia, also occurring in Southern Asia
Rats and mice cause losses in a number of ways:
- Feeding on stored produce
Rats eat an amount of food equivalent to 7% of their body weight daily, i.e. a rat with a body weight of 250 g will eat around 25 g daily, amounting to 6.5 kg of grain a year. Mice eat a daily amount equivalent to around 15% of their body weight, i.e. a mouse weighing 25 g will eat between 3 and 4 g a day, amounting to 1.4 kg of grain a year. Besides feeding on stored produce, actual losses are much higher, as rodents contaminate the stored produce with urine, faeces, hair and pathogenic agents. As it is extremely difficult if not impossible to remove filth produced by rodents from the stored produce, infested batches often have to be declared unfit for human consumption.
There are around 50 diseases which can be transferred to man by rodents, including typhoid, paratyphoid, and scabies. In addition, rodents may be vectors of a large number of diseases affecting domestic animals. The problems and costs resulting from these diseases are not normally taken into account when assessing infestation by rodents.
As rodents prefer food rich in proteins and vitamins and feed mainly on the embryo, they cause particular damage to the nutritional value and germination ability of seeds.
- Damage to material and equipment (e.g. tarpaulins, bags, pallets, sprayers) and to the store itself (cables, doors).
These often lead to subsequent damage:
· Produce leaking out of damaged bags or storage containers
· Bags stacks collapsing due to damage to the lower layers
· Short circuits leading to sparks or fire from cables being chewed
· Silos and warehouses may subside or even collapse as a result of being undermined
· Drainage canals around a store may be damaged.
Signs of rodent infestation
When there are signs of rodent infestation, it is necessary to conduct a thorough investigation of the store, its immediate surrounding area and neighbouring land.
There are a large number of clear signs of rodent infestation:
Live animals
Rodents are mainly active at night. If animals are nonetheless seen during the daytime, this is a sign of an already advanced stage of infestation.
Droppings
The shape, size and appearance of droppings can provide information as to the species of rodent and the degree of infestation. The droppings of Norway rats are around 20 mm in length and are found along their runs. The droppings of Black rats are around 15 mm long and are shaped like a banana. Mouse droppings are between 3 and 8 mm in length and irregular in shape. Droppings are soft and shiny when fresh, becoming crumbly and matt black or grey in colour after 2 - 3 days.
Runs and tracks
Runs, such as those of Norway rats, are to be found along the foot of walls, fences or across rubble. They virtually never cross open areas of land, but always pass through overgrown territory, often being concealed by long grass.
Runs inside buildings can be recognized by the fact that they are free of dust. The animal's fur coming into contact with the wall leaves dark, greasy stains. Even Black rats, which do not have any fixed runs, can leave similar greasy stains at points which they pass regularly, e.g. when climbing over roof beams.
Footprints and tail marks
Rats and mice leave footprints and tail marks in the dust. If you suspect there might be rodent infestation, scatter some sort of powder (talcum powder, flour) on the door at several places in the store and later check for traces. The size of the back feet serves as an indication of the species of rodent:
· Back feet larger than 30 mm: Black rat, Norway rat, Bandicoot rat.
· Back feet smaller than 30 mm: House mouse, Multi-mammate rat, Pacific rat.
Tell-tale damage
Rats leave relatively large fragments of grain they have nibbled at (gnaw marks). They generally only eat the embryo of maize. Sharp and small leftovers are typical for mice. Rodent attack can further be detected by damaged sacks where grain is spilled and scattered. Small heaps of grain beneath bag stacks are a clear sign. These should be checked for using a torch on regular controls.
Attention should be paid to damaged doors, cables and other material.
Burrows and nests
Depending on their habits, rodents either build nests inside the store in corners as well as in the roof area or in burrows outside the store. Rat holes have a diameter of between 6 and 8 cm, whereas mice holes are around 2 cm in diameter. These holes can be found particularly in overgrown areas or close to the foundations of a store.
Urine
Urine traces are fluorescent in ultraviolet light. Where available, ultraviolet lamps can be used to look for traces of urine.
Preventive measures
The most essential factors for the occurrence of rodents are:
· sufficient supplies of food
· protected places in which to build burrows and nests
· hiding places
· access to produce
Good store management and preventive measures taken as part of an integrated control programme can help to deal with these factors.
Storage Hygiene and Technical Measures
· Keep the store absolutely clean! Remove any spilt grain immediately as it attracts rodents!
· Store bags in tidy stacks set up on pallets, ensuring that there is a space of I m all round the stack!
· Store any empty or old bags and fumigation sheets on pallets, and if possible in separate stores!
· Keep the store free of rubbish in order not to provide the animals with any places to hide or nest! Bum or bury it!
· Keep the area surrounding the store free of tall weeds so as not to give the animals any cover! They have an aversion to crossing open spaces.
· Keep the area in the vicinity of the store free of any stagnant water and ensure that rainwater is drained away, as it can be used as source of drinking water.
Keeping Rodents Out
The requirements of preventive rodent control must be taken into account whenever new stores are being built. Particular attention should be paid to doors, ventilation openings, brickwork and the junctions between the roof and the walls. Repair any damage to the store immediately! This applies especially to the doors.