In parts of India, between 72 and 100 per cent of the storage insects in grain warehouses are resistant to the fumigant used to kill them.
At the upper end of that range the chemical has stopped working altogether. And the chemical in question is not a minor one: aluminium phosphide has been the mainstay of protecting India's grain reserves for decades, alongside malathion. A country that holds a buffer stock measured in tens of millions of tonnes has been defending it with a weapon its enemy has largely learned to survive.
On 30 September 2026, the Indian Council of Agricultural Research (ICAR) and the Food Corporation of India (FCI) signed a Memorandum of Understanding to research alternatives. The project is supported by the Department of Food and Public Distribution and will be implemented by ICAR-CIPHET — the Central Institute of Post-Harvest Engineering and Technology, Ludhiana.
How resistance happens, and why it was inevitable
Aluminium phosphide is a solid that reacts with atmospheric moisture to release phosphine (PH₃), a gas that penetrates a grain mass and kills insects by interfering with their cellular respiration — broadly, by disrupting mitochondrial function and the enzymes involved in energy metabolism.
Because phosphine acts through specific biochemical pathways, there are specific biochemical ways to survive it. In any large insect population a few individuals carry mutations — in genes affecting the metabolism of the toxicant, or the target enzymes themselves — that let them tolerate a dose that kills the rest. Fumigate repeatedly and you remove the susceptible insects and leave the tolerant ones to breed. Do it for decades and the tolerant strain becomes the population. This is natural selection operating on a timescale of months, with the warehouse manager as the selecting agent.
Three features of Indian grain storage accelerated it, and all three appear in the official account.
Repetition. Grain in central reserves is stored for long periods and fumigated again and again. Each cycle is another round of selection.
Imperfect sealing. Phosphine kills reliably only if a lethal concentration is held for long enough. A bag stack under a tarpaulin leaks; concentration falls below lethal; insects receive a sub-lethal dose. Sub-lethal exposure is the ideal condition for breeding resistance, because it kills the weakest and spares everything else.
Escalating cycles. As resistance rises, operators respond with more frequent fumigation — which is more selection pressure. The official statement names the consequence: "escalating fumigation cycles that drive up operational costs". The chemical becomes less effective and more expensive at the same time.
There is a human cost too. Phosphine is acutely toxic to people, and the release notes that current chemical methods "pose significant respiratory threats to workers and long-term ecological risks", along with concerns about fumigant residues in food.
The alternative, and why it is resistance-proof
The project will standardise the commercial use of nitrogen gas, carbon dioxide, and a synergistic combination of carbon dioxide and phosphine.
Nitrogen and carbon dioxide are not poisons. They work by displacing oxygen — filling the void spaces in a grain mass with an inert or near-inert gas until the atmosphere can no longer support insect respiration. The insect does not metabolise a toxin; it suffocates. This is controlled atmosphere storage, and it is the conceptual heart of the whole initiative.
Here is why that matters, and it is the single most important idea in this story. An insect can evolve resistance to a toxic molecule. It cannot evolve its way out of needing oxygen. Resistance arises when a mutation alters how an organism metabolises a poison or what the poison binds to. There is no mutation that removes an insect's requirement for aerobic respiration. Controlled atmosphere methods are therefore, in a meaningful sense, resistance-proof — not merely new chemicals that pests have yet to adapt to, but a mechanism to which adaptation is not available.
Carbon dioxide adds a second effect: at high concentrations it is not merely an oxygen displacer but physiologically active, opening the insect's spiracles and increasing its uptake of whatever else is present. Which explains the third trial.
The CO₂-plus-phosphine synergy uses that property deliberately. Raising CO₂ forces insects to respire more actively, so they take up more phosphine — allowing a lower phosphine dose to achieve a lethal effect. That means less chemical, lower residues, reduced worker exposure, and, critically, a more reliably lethal dose, which slows resistance rather than accelerating it.
The three trials
Phase I runs for two years, with three trials:
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Nitrogen gas (greater than 99%) against storage pests in wheat stored in metal silos. Silos matter here: a sealed steel silo can hold a modified atmosphere, which a bag stack cannot. The gas and the container are a package.
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Combined carbon dioxide and phosphine against pests in wheat and rice stored in bags at FCI and Central Warehousing Corporation warehouses — the realistic case, because most Indian grain is still in bags in conventional godowns.
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Carbon dioxide against pests in wheat and rice in bags enclosed in hermetic covers. A hermetic cover is a gas-tight enclosure, and it is the bridge technology — it confers silo-like sealing on bagged grain without rebuilding the warehouse.
Phase II will follow with a one-year multi-location trial across varied agro-climatic zones to establish region-specific Standard Operating Procedures.
That last point is not a formality. Fumigation outcomes depend on temperature and humidity — gas behaviour, insect metabolism and the rate at which aluminium phosphide hydrolyses all vary with ambient conditions. A protocol calibrated in Ludhiana will not transfer unchanged to coastal Kerala or to Rajasthan, and a single national SOP would fail somewhere. Building region-specific protocols is the difference between a research finding and an operational method.
Why this is a large problem wearing small clothes
An MoU on fumigation chemistry sounds like a technical footnote. Consider the scale behind it.
India procures and stores grain on a scale few countries attempt, as the foundation of the public distribution system. Every tonne lost to insects is a tonne procured from a farmer, transported, stored, and then thrown away — the fiscal cost of the procurement plus the storage plus the loss, with no nutritional benefit to anybody. Storage losses are the quietest line item in India's food economy and among the most consequential.
The infrastructure response to this problem is the construction of modern silos and the decentralised village-level storage being built through cooperatives. But a silo does not kill insects; it only makes it possible to kill them properly. Steel capacity without a working fumigation protocol is a better-sealed warehouse full of resistant pests. The chemistry and the concrete have to arrive together, and this MoU is the chemistry — just as the logistics of moving a buffer stock to market is the part of food management that only becomes visible when it fails.
🔑 Revision block
- MoU signed 30 September 2026 between ICAR and FCI, supported by the Department of Food and Public Distribution (DFPD), on alternative fumigation technologies for storage pests in wheat and rice.
- Implemented by ICAR-CIPHET — Central Institute of Post-Harvest Engineering and Technology, Ludhiana. Phase I: two years.
- Current fumigants: aluminium phosphide (ALP) and malathion.
- Aluminium phosphide reacts with atmospheric moisture to release phosphine (PH₃), which kills insects by disrupting cellular respiration.
- Pest resistance frequencies have reached 72-100% in key Indian states.
- Why resistance arose: repeated fumigation of long-stored grain; imperfect sealing producing sub-lethal doses; and escalating fumigation cycles raising both resistance and cost. Also worker respiratory risk, ecological risk and residues.
- The alternatives: nitrogen gas, carbon dioxide, and a synergistic CO₂ + phosphine combination — controlled atmosphere storage.
- Key principle: nitrogen and CO₂ kill by displacing oxygen — physical asphyxiation, not biochemical toxicity. An insect can evolve resistance to a toxic molecule but not to the absence of oxygen.
- CO₂ synergy: high CO₂ opens insect spiracles and raises respiration, increasing phosphine uptake — so a lower phosphine dose becomes lethal, cutting residues and slowing resistance.
- Three Phase-I trials: (1) nitrogen >99% for wheat in metal silos; (2) CO₂ + phosphine for wheat and rice in bags at FCI/CWC warehouses; (3) CO₂ for wheat and rice in bags under hermetic covers.
- A hermetic cover is a gas-tight enclosure — it gives bagged grain silo-like sealing without rebuilding the warehouse.
- Phase II: one-year multi-location trial across agro-climatic zones to set region-specific SOPs — necessary because gas behaviour, insect metabolism and ALP hydrolysis all vary with temperature and humidity.
- People: Dr M.L. Jat, Secretary DARE and Director General, ICAR; Dr Nachiket Kotwaliwale, Director, ICAR-CIPHET; Dr A.K. Sinha, Executive Director (Quality Control), FCI.
🎯 Practice MCQs
Q1. Aluminium phosphide acts as a fumigant because it: (a) Absorbs moisture and dehydrates insects (b) Coats grain surfaces with an insecticidal film (c) Reacts with atmospheric moisture to release phosphine gas (d) Raises the temperature of the grain mass
→ (c) Aluminium phosphide is a solid that hydrolyses on contact with atmospheric moisture to release phosphine (PH₃), which penetrates the grain mass and disrupts insect cellular respiration.
Q2. Reported resistance frequencies to current fumigants among storage pests in key Indian states have reached: (a) 20-30% (b) 72-100% (c) 10-15% (d) 45-55%
→ (b) 72-100% — meaning that at the upper end of the range the fumigant has effectively ceased to work on the local pest population.
Q3. Nitrogen and carbon dioxide fumigation control storage pests principally by: (a) Displacing oxygen so that insect respiration cannot be sustained (b) Denaturing the enzymes of the insect gut (c) Interfering with insect reproductive hormones (d) Altering the pH of the grain surface
→ (a) They work by displacing oxygen — a physical mechanism. This is controlled atmosphere storage, and the insect suffocates rather than being poisoned.
Q4. Insects are considered unable to develop resistance to controlled atmosphere methods in the way they do to phosphine because: (a) These gases are used at much higher concentrations (b) There is no mutation that removes an organism's requirement for oxygen (c) The gases are applied only in sealed metal silos (d) Carbon dioxide destroys insect DNA directly
→ (b) Resistance arises from mutations altering a toxicant's metabolism or its target site. Needing oxygen is not a target that can be mutated away, which makes asphyxiation effectively resistance-proof.
Q5. The rationale for combining carbon dioxide with phosphine is that elevated CO₂: (a) Chemically converts phosphine into a more stable compound (b) Prevents phosphine from escaping the grain mass (c) Neutralises phosphine residues in the grain (d) Opens insect spiracles and raises respiration, increasing phosphine uptake
→ (d) High CO₂ is physiologically active: it opens the spiracles and increases respiration, so insects take up more phosphine. A lower phosphine dose then suffices, reducing residues and worker exposure while delivering a more reliably lethal dose.
Q6. Imperfect sealing of a grain stack accelerates the development of resistance because it results in: (a) Higher fumigant residues in the grain (b) Faster hydrolysis of aluminium phosphide (c) Sub-lethal doses that kill only the most susceptible insects (d) Complete loss of the fumigant before it acts
→ (c) A leaking enclosure lets concentration fall below the lethal threshold, so insects receive a sub-lethal dose. That is the ideal condition for selecting resistance, since it removes the weakest and spares the rest to breed.
Q7. In the Phase-I trials, nitrogen gas of greater than 99% purity is to be tested on wheat stored in: (a) Bags under hermetic covers (b) Open plinths (c) Jute bags in conventional godowns (d) Metal silos
→ (d) Nitrogen is to be trialled in metal silos, because a sealed steel structure can hold a modified atmosphere. Hermetic covers are the subject of a separate CO₂ trial, and bagged grain in FCI/CWC warehouses is the CO₂-plus-phosphine trial.
Q8. A 'hermetic' cover in grain storage refers to an enclosure that is: (a) Insulated against temperature change (b) Gas-tight, allowing a modified atmosphere to be maintained (c) Treated with a contact insecticide (d) Permeable to moisture but not to insects
→ (b) A hermetic enclosure is gas-tight. It is the bridge technology that confers silo-like sealing on bagged grain without rebuilding the warehouse.
Q9. Phase II of the project will establish region-specific Standard Operating Procedures because: (a) Gas behaviour, insect metabolism and fumigant release all vary with temperature and humidity (b) Each state has its own food safety regulator (c) Grain varieties differ between states (d) Only some states permit controlled atmosphere storage
→ (a) Fumigation outcomes depend on ambient temperature and humidity, which govern gas behaviour, insect metabolism and the rate at which aluminium phosphide hydrolyses. A protocol calibrated in one agro-climatic zone will not transfer unchanged to another.
Q10. ICAR-CIPHET, the implementing institute, specialises in: (a) Post-harvest engineering and technology (b) Plant genetic resources (c) Soil science and land-use planning (d) Agricultural economics and policy research
→ (a) CIPHET is the Central Institute of Post-Harvest Engineering and Technology, Ludhiana — the ICAR institute concerned with what happens to a crop after it leaves the field, which is precisely where storage losses occur.
📋 How this gets asked (PYQ pattern)
This topic sits in a part of the syllabus that candidates under-prepare, which makes it good value.
The first pattern is ICAR institutes and their mandates. CIPHET for post-harvest engineering, IARI for agricultural research at Pusa, NBPGR for plant genetic resources, IIHR for horticulture, CAZRI for arid zones, IISR for sugarcane. Each has a location and a subject, and questions pair them.
The second is applied chemistry and biology, which is where the marks are. Aluminium phosphide releasing phosphine on hydrolysis is a straightforward chemical reaction; oxygen displacement as a control mechanism is straightforward biology; the distinction between a physical and a biochemical mode of action is the kind of conceptual point papers increasingly favour, because it cannot be answered by memorisation.
The third is resistance and natural selection, a theme that recurs across the syllabus — antimicrobial resistance, pesticide resistance, herbicide-tolerant weeds. The mechanism is identical in each case: a population under repeated selective pressure, with sub-lethal exposure as the accelerant. Learn it once and it answers questions in three different chapters.
The fourth is food management institutions: FCI for procurement and storage, CWC for warehousing, DFPD for policy, NAFED for market intervention. Candidates confuse FCI with CWC routinely, and the distinction is simply that FCI holds the central pool while CWC provides warehousing as a service.
Preparing for CDS/OTA? When a scheme or study concerns resistance — to a drug, a pesticide or a fumigant — the examinable idea is always the same: selection pressure plus sub-lethal exposure. Learn that mechanism once, and it covers AMR, pest control and weed science together. Build the base with our CDS/OTA study material, follow the daily CDS current affairs, and prepare with our faculty in the upcoming Cavalier courses in Delhi.
✍️ Written by The Cavalier — Science and technology desk at The Cavalier. Reviewed by the Cavalier Faculty Desk.