In order to save the stored food grains from insects, farmers usually mix with them

Correct — A, (a) Neem leaves. The practice is old, it is universal in rural India, and the school textbook states it plainly: dried neem leaves are used for storing food grains at home. The leaves are mixed in with the grain in the bin, drum or gunny bag, and they keep the storage pests away.

The reason lies in the chemistry of the neem tree, Azadirachta indica. Its tissues contain a family of bitter triterpenoid compounds of the limonoid group, of which azadirachtin is the best known, most concentrated in the seed but present in the leaves too. Azadirachtin does not kill insects the way a contact poison does. It works as an antifeedant, deterring insects from eating treated material; as a repellent; and as a growth disruptor, interfering with the hormones that control moulting and development, so that larvae fail to pupate and reproduction is impaired. It is effective against a very wide range of species and is registered as a biopesticide fit for use in organic farming. For grain that a family will eat, those properties are exactly right: the leaves protect the stock without leaving a toxic residue on the food.

The practice sits inside a larger routine of storage, which is worth having in full because it is the examinable part. The grain is first dried properly in the sun to reduce its moisture, since damp grain is attacked by insect pests, bacteria and fungi and may be rendered unfit for eating or for sowing. It is then stored — in jute bags or metallic bins at home, in silos and granaries for large quantities, to keep out rats and insects. Neem leaves serve the household scale. For large stocks in godowns, specific chemical treatments are used instead, most commonly fumigation.

Why the others are wrong

• (b)Mango leaves — Mango leaves have a strong cultural presence in Indian households — strung as a toran across a doorway at festivals and weddings, and used in ritual — and that familiarity is what puts this option on the page. They have no recognised use as a grain protectant and no comparable insect-deterrent chemistry. The general point is worth taking: a plant may be culturally prominent, medicinally useful, or agriculturally valuable without being any of the others, and questions of this kind exploit the tendency to run the three together.
• (c)Peepal leaves — The peepal, Ficus religiosa, is among the most venerated trees in India and is well known for other reasons — it is long-lived, it is a keystone species for birds and insects because of its figs, and it is often the tree left standing when everything around it has been cleared. None of that gives its leaves any role in protecting stored grain. As with mango, the option trades on reverence rather than on any property of the leaf.
• (d)Orange leaves — Orange leaves are not used for storing grain. The citrus association a candidate may be reaching for is real but belongs elsewhere: citrus peel contains limonene, an aromatic oil with some insect-repellent properties, and dried peel is occasionally used in household pest deterrence. The leaves are not the part used, the effect is much weaker than neem’s, and the practice is not the one Indian farmers follow. This option is the closest thing to a scientific near-miss among the three wrong answers, and it is still some way off.

Storage is the last of the agricultural practices in the crop production cycle — preparation of soil, sowing, adding manure and fertilisers, irrigation, protection from weeds, harvesting, and then storage — and it is where a large part of India’s food loss occurs. The threats to stored grain are moisture, insects, rodents and micro-organisms, and each has its counter. Moisture is dealt with first, by drying the grain in the sun before storage; damp grain is attacked by insect pests, bacteria and fungi and may become unfit for eating or for sowing, and fungal growth in stored grain also carries the risk of mycotoxins. Insects and rodents are dealt with by the container and by the treatment: jute bags and metallic bins at household scale, silos and granaries at commercial scale, and dried neem leaves mixed into household stocks. Large godowns use chemical treatments and fumigation instead. The neem tree is a genuinely remarkable source of such protection. Every part of it is bitter, the seeds most of all, and the active limonoids led by azadirachtin act as antifeedants, repellents and growth disruptors rather than as simple poisons. Neem has been used in India for pest management for a very long time, and neem-based formulations are now among the most widely used botanical pesticides in the world, valued particularly in organic cultivation because they break down quickly and leave no persistent residue.

Key facts

• Dried neem leaves are used for storing food grains at home, mixed in with the grain to keep insect pests away.
• The neem tree is Azadirachta indica; its principal insecticidal compound is azadirachtin, a triterpenoid of the limonoid group.
• Azadirachtin is most concentrated in the seeds and acts as an antifeedant, a repellent and a disruptor of insect growth and reproduction rather than as a contact poison.
• It is effective against a very wide range of insect species and is registered as a biopesticide suitable for organic farming.
• Grain is dried in the sun before storage to reduce its moisture, which prevents attack by insect pests, bacteria and fungi.
• Damp grain may be spoiled to the point of being unfit for eating or for germination.
• Farmers store grain in jute bags or metallic bins; large-scale storage uses silos and granaries to protect against rats and insects.
• Large quantities of grain in godowns are protected by specific chemical treatments, most commonly fumigation.

Common traps

• Choosing a leaf because the tree is culturally important. Mango and peepal are revered; neither protects grain.
• Forgetting the drying step. Reducing moisture comes before storage and is what prevents fungal and bacterial attack.
• Assuming neem works as a poison. It works chiefly by deterring feeding and disrupting insect development.
• Applying the household remedy to large stocks. Godown-scale storage uses chemical treatment, not neem leaves.

• practice — not a real PYQ

  Before grains are stored, they are dried in the sun principally to

  • (a)improve their taste
  • (b)reduce their moisture content and so prevent attack by insects, bacteria and fungi
  • (c)increase their weight
  • (d)improve their rate of germination

  Answer(b) reduce their moisture content and so prevent attack by insects, bacteria and fungi

• practice — not a real PYQ

  The principal insecticidal compound obtained from the neem tree is

  • (a)pyrethrin
  • (b)rotenone
  • (c)azadirachtin
  • (d)nicotine

  Answer(c) azadirachtin