Lecture notes on pests of stored grains

1.Sitophilus oryzae
Commonly called the rice weevil. It is the commonest and the most destructive pest of stored grains, such as rice, maize, wheat, barley, bajara, etc. It enjoys worldwide distribution. Sitophilus oryzae is distinct from the allied species S.granarius. Both them are somewhat similar in appearance and size, and may be found together.
Adult weevils are somewhat cylindrical and reddish-brown or brownish-black, with prolonged thorax, head and snout or rostrum, chewing type of mouth-parts and ridged elytra.
Life cycle:
Their life span is 4-5 months. Most of the time they remain inside grains for feeding. But, mating usually takes place outside the grains. Soon after mating, female weevil makes pits or cavities in the kernel of the grain, deposits eggs in them at the rate of one egg in each cavity and seals their mouth with a plug of gelatinous secretion. A female may lay as many as 400eggs. In about 6 or 7 days, eggs hatch out into soft, white and legless grubs (larvae). They bore into Sitophilus the grains and actively feed on the interior of the grain, hollowing it out. After 3 or 4 weeks, larvae
change to pupae. Initially, pupae are dirty white. But, later on, they become dark-brow and curved. Pupal life lasts for 6-14 days. Adult weevils come out through irregular
holes made in the grain. The whole life cycle is completed inside the grain passing through a period of 4-7 weeks.
Damage caused
Sitophilus oryzae is  the most destructive of all grain pests. Its l adults and larvae feed on stored grains and damage the beyond use. Often, it causes almost complete destruction of grains in granaries, ships, storage bins, etc., especially during the mon- soon season. This accounts for considerable loss of food grains.
Control measures
1.Cleaning of godowns, store rooms, storage bins, bags, etc. to make them free from
2.Disinfection of stored grains by fumigation and also by dusting of BHC and other insecticides.
3. Periodic fumigation with methyl bromide, ethylene dibromide, ethylene dichloride.
4.Through drying  of grains before storage to reduce moisture contents.

2.Callasobruchus chinensis
Commonly called the pulse beetle, is a serious pest of grams, peas, sorghum, maize cotton seed. ete., both in field crops and stores.
Distribution
Enjoys wide distribution in India, Myanmar, China, Taiwan, Sri Lanka, Japan, Philippines and Indonesia.
Life cycle
Adult beetle is small and cylindrieal, with deflexed head and blunt anal end It is shining black or dark brown in colour Antennne are terminally club shaped
Breeding occurs from March to September Vemale lays as many as 300-400 cylindrical and glistening white eggs in 20-60 day after mating They are glued to the grains in batches, Larvae (grubs) hatch out in 5-9 days. Their body is long and constricted, and dirty white in colour. They crawl about and feed on the flour, or bore into slightly damaged grains and feed inside them. Larval life lasts for 22- 52 days Full-grown larvae are  and curved They pupate inside the grains, or in the grain flour Pupal stage lusts for neurly 7 days. Adults emerge from within the grains after makingrounded holes. There would be 5 or 6 generations in a year
Damage
Adults and larvne cause serious damages to pulses and grains
They bore into pulses and grains
and feed inside them making tunnels. This severely hollows out und damages pules and In heavy infestation, avconsiderable amount of frass is formed, which forms the food for the young larva- Often, the pest attacks leguminous pods in the field, before they are curied to storage godowns
Control measures
(i) Thoroughly dry grains and other food products before storage
(ii) Clean and disinfect godowns, flour mills, storage bins, bags, etc. before storing food products.
(iii) Destroy infested food products.
(iv) Treat food products with mild insecticides before storage
(v) Periodic fumigation with methyl bromide, ethylene dibromide, etc. to kill larva and adults.