Insect pests and their management

In short

Insect pests are insect species whose feeding, egg-laying or disease transmission reduces crop yield or quality below an acceptable level; they destroy roughly 15-25% of India's standing crop output, with losses varying widely by crop and season. Managing them needs correct identification of the insect and its damage symptom, knowledge of its life cycle and the right control at the right stage. This topic carries the largest share of marks in Entomology papers of B.Sc (Ag) and in ICAR JRF/SRF, IBPS AFO, NABARD Grade A, state Agriculture Officer and ADO exams. In jobs it is the daily work of field officers at Bayer, Syngenta, UPL, Coromandel, Rallis, Dhanuka, FPOs and Krishi Vigyan Kendras, and of the Plant Protection wing of state agriculture departments.

Explained

Insect structure, damage and classification of pests

• Insecta: body in head, thorax, abdomen; three pairs of legs, usually two pairs of wings, one pair of antennae, compound eyes, tracheal respiration through spiracles, open circulatory system with haemolymph.
• Mouthparts decide the damage symptom and the insecticide needed:
  • Biting and chewing (Orthoptera, most Coleoptera, lepidopteran larvae) - holes, notching, defoliation, tunnelling; controlled by stomach poisons and bait.
  • Piercing and sucking (Hemiptera, Thysanoptera - rasping-sucking) - yellowing, curling, hopperburn, honeydew with sooty mould, virus transmission; need systemic or contact insecticides, not stomach poisons.
  • Siphoning (adult Lepidoptera - harmless, nectar feeders), sponging (house fly), chewing-lapping (honeybee - a pollinator to protect).
• Metamorphosis: ametabolous (no change), hemimetabolous/paurometabolous - egg, nymph, adult (hoppers, bugs, grasshoppers), holometabolous - egg, larva, pupa, adult (moths, beetles, flies). Larval types: eruciform (caterpillar), scarabaeiform (grub), elateriform (wireworm), vermiform (maggot), campodeiform (predatory grubs).
• Pest categories by status: regular/key pest (appears every season - stem borer in rice), occasional pest, seasonal pest, sporadic pest, persistent pest, epidemic/outbreak pest, minor pest, potential pest, monophagous/oligophagous/polyphagous by host range.
• Pest of national significance: locust (Schistocerca gregaria) - handled by the Locust Warning Organisation, Jodhpur, under the Directorate of Plant Protection, Quarantine and Storage (DPPQS), Faridabad.

Economic concepts in pest management

• Economic damage: the amount of injury that justifies the cost of control.
• Economic injury level (EIL): the lowest pest density that will cause economic damage - the break-even point.
• Economic threshold level (ETL)/action threshold: the density at which control must be started so the population never reaches EIL; ETL is always below EIL because control takes time to act.
• General equilibrium position (GEP): the average density of a pest over a long period in the absence of permanent change; damage boundary - the lowest injury measurable.
• Key ETLs used in Indian advisories (indicative; state package-of-practices values differ):
  • Rice yellow stem borer - 5% dead hearts or 1 egg mass/m²; 2 moths/trap/night in pheromone traps.
  • Rice brown planthopper - 5-10 hoppers/hill (fewer if natural enemies absent).
  • Cotton bollworms - 10% damaged squares/bolls, or 8 pink bollworm moths/trap/night for 3 consecutive nights.
  • Cotton jassid - 1-2 nymphs/leaf with grade-1 hopper burn; whitefly 6-8 adults/leaf.
  • Fall armyworm in maize - 5% whorl damage in early whorl stage, 10% in late whorl, 10% ear damage.
  • Gram pod borer (Helicoverpa) - 1 larva/plant or 5 moths/trap/night.
• Field assessment needs a sampling plan: unit (leaf, hill, plant, m², sweep net), number of samples, randomisation, and the time of day (hoppers at base of hill, early morning; thrips inside buds).

Major insect pests of Indian crops - pest, damage, management

• Rice:
  • Yellow stem borer (Scirpophaga incertulas, Crambidae) - "dead heart" in vegetative stage, white ear head in reproductive stage. Manage by clipping seedling tips, destroying stubbles, light and pheromone traps, release of *Trichogramma japonicum* at 1 lakh/ha/week, cartap hydrochloride or chlorantraniliprole at ETL.
  • Brown planthopper (Nilaparvata lugens, Delphacidae) - sucks phloem at plant base, causes circular hopperburn; favoured by close spacing, excess nitrogen and continuous flooding. Manage by alleyways, draining the field, avoiding excess N, resistant varieties, conserving mirid bug *Cyrtorhinus* and spiders; pymetrozine/dinotefuran/triflumezopyrim. Avoid synthetic pyrethroids - they cause resurgence by killing natural enemies.
  • Gall midge (Orseolia oryzae) - silver shoot/onion shoot; leaf folder (Cnaphalocrocis medinalis) - leaves folded, white papery streaks; rice hispa, case worm, gundhi bug (Leptocorisa - causes chaffy, spotted grains).
• Cotton:
  • Pink bollworm (Pectinophora gossypiella) - the key pest now, having developed resistance to Bt (Cry1Ac/Cry2Ab) cotton; rosette flower, interlocked locules. Manage by timely sowing, strict termination of the crop (no extension into a second season), destruction of crop residue, pheromone (gossyplure) traps at 5/ha for monitoring and 40/ha for mass trapping, *Trichogramma bactrae* release.
  • American bollworm (Helicoverpa armigera), spotted bollworm (Earias spp.), whitefly (Bemisia tabaci - vector of cotton leaf curl virus), jassid (Amrasca biguttula biguttula), thrips, aphid, mealybug (Phenacoccus solenopsis).
• Pulses: gram pod borer (Helicoverpa armigera) - manage with bird perches at 20-25/ha, HaNPV at 250 larval equivalents/ha, neem 1500 ppm, pheromone traps; spotted pod borer (Maruca vitrata), pulse beetle (Callosobruchus - storage), stem fly (Ophiomyia phaseoli).
• Maize: fall armyworm (Spodoptera frugiperda, invasive since 2018, first reported in Karnataka) - whorl feeding with ragged holes and moist frass; manage by whorl application of sand + insecticide, emamectin benzoate/spinetoram/chlorantraniliprole as per CIB&RC label, *Telenomus remus* egg parasitoid, maize-pulse intercropping, early uniform sowing. Pink stem borer, shoot fly (Atherigona - in sorghum, dead heart, manage by seed treatment with imidacloprid and timely sowing).
• Sugarcane: early shoot borer (Chilo infuscatellus - dead heart in 1-3 months, manage by trash mulching and irrigation), top shoot borer (Scirpophaga excerptalis - bunchy top), internode borer, pyrilla (Pyrilla perpusilla - controlled naturally by the parasitoid *Epiricania melanoleuca*), woolly aphid, termites.
• Vegetables: brinjal shoot and fruit borer (Leucinodes orbonalis - the reason Bt brinjal was proposed; manage by clipping affected shoots weekly, pheromone traps, *Trichogramma chilonis*), diamondback moth on cabbage (Plutella xylostella - mustard trap crop at 25:2 rows, *Diadegma semiclausum*), fruit fly (Bactrocera cucurbitae/dorsalis - cue-lure and methyl eugenol traps), tomato pinworm (Phthorimaea absoluta, invasive 2014), onion thrips.
• Oilseeds and others: mustard aphid (Lipaphis erysimi - the key pest, ETL 50-60 aphids/10 cm terminal twig), castor semilooper, tea mosquito bug on cashew, coconut rhinoceros beetle and red palm weevil, mango hopper and mango fruit fly, grapevine mealybug.
• Stored grain pests: lesser grain borer (Rhyzopertha dominica), rice weevil (Sitophilus oryzae), khapra beetle (Trogoderma granarium - an external feeder of great quarantine importance), angoumois grain moth, red flour beetle (Tribolium - secondary pest, feeds only on broken grain). Control by drying grain to safe moisture (below about 10-12% for cereals), airtight storage, and fumigation with aluminium phosphide (3 g tablet/tonne) by trained operators only.

Control methods

1. Cultural: deep summer ploughing, crop rotation, timely and uniform sowing, trap crops (marigold for Helicoverpa, mustard for DBM), intercropping, destruction of stubble and alternate hosts, balanced fertiliser (excess N raises sucking-pest build-up), clean cultivation, water management.
2. Mechanical and physical: hand collection and destruction of egg masses and larvae, shaking and collecting (*Helicoverpa*), light traps (one per ha), yellow and blue sticky traps (whitefly/aphid, thrips), bird perches, barriers and trenches for armyworm, solar heat and hot-water treatment, hermetic storage, irradiation.
3. Biological: parasitoids (*Trichogramma*, *Bracon*, *Chelonus*, *Telenomus*, *Apanteles*, *Encarsia formosa*), predators (lady bird beetle *Cheilomenes*, *Chrysoperla zastrowi sillemi*, mirid bugs, spiders, *Cryptolaemus montrouzieri* for mealybug), entomopathogens - NPV (HaNPV, SlNPV), *Bacillus thuringiensis* var. *kurstaki*, *Beauveria bassiana*, *Metarhizium anisopliae*, *Lecanicillium (Verticillium) lecanii*, EPN *Heterorhabditis*.
4. Host plant resistance: antixenosis (non-preference), antibiosis, tolerance; transgenics - Bt cotton (only Bt cotton is approved for commercial cultivation in India; Bt brinjal and HT cotton are not approved).
5. Behavioural/biorational: pheromones (monitoring, mass trapping, mating disruption), attractants (methyl eugenol, cue-lure), antifeedants (neem azadirachtin), insect growth regulators - chitin-synthesis inhibitors (diflubenzuron, novaluron), juvenile hormone analogues (pyriproxyfen), moulting accelerators (methoxyfenozide).
6. Legislative: quarantine and the Destructive Insects and Pests Act, 1914 with the Plant Quarantine (Regulation of Import into India) Order, 2003; pesticide regulation under the Insecticides Act, 1968.
7. Chemical: the last resort, at ETL, with the right molecule, dose, water volume, nozzle and waiting period.

Insecticides - classification, mode of action, safety

• By mode of entry: contact, stomach, fumigant, systemic (taken up and translocated - effective on sucking pests and concealed feeders).
• By chemical group:
  • Organochlorines - DDT, BHC, endosulfan (banned/withdrawn in India; endosulfan under Supreme Court ban since 2011).
  • Organophosphates - chlorpyriphos, dimethoate, acephate, profenofos; acetylcholinesterase inhibitors.
  • Carbamates - carbaryl, carbosulfan; also AChE inhibitors (reversible).
  • Synthetic pyrethroids - cypermethrin, deltamethrin, lambda-cyhalothrin; sodium channel modulators; cause resurgence and mite flare-up.
  • Neonicotinoids - imidacloprid, thiamethoxam, acetamiprid; nicotinic acetylcholine receptor agonists; highly systemic; hazardous to honeybees.
  • Diamides - chlorantraniliprole, flubendiamide; ryanodine receptor activators; excellent on Lepidoptera.
  • Avermectins/spinosyns - emamectin benzoate, spinosad (chloride channel and nAChR allosteric action); METI acaricides - fenazaquin; pyridine azomethines - pymetrozine (feeding blocker).
  • Botanicals - neem (azadirachtin 300/1500/10000 ppm), pyrethrum, karanj; biopesticides - Bt, NPV, fungi.
• Formulations: EC, WP, SC/FS, SL, SP, SG, WG/WDG, G, D, ULV, CS; newer water-based formulations (SC, WG) are safer and dust-free.
• Toxicity labelling under the Insecticides Rules, 1971: triangle colour by oral LD50 - bright red (extremely toxic), bright yellow (highly toxic), bright blue (moderately toxic), bright green (slightly toxic).
• Regulation: Insecticides Act, 1968 and Rules, 1971 - CIB&RC (Central Insecticides Board and Registration Committee) registers molecules under Section 9(3)/9(3B)/9(4); Central Insecticides Laboratory tests quality; state licensing of manufacture, sale and custom application; only label-claim use is legal. MRL and waiting period are notified under the Food Safety and Standards Act, 2006 (FSSAI). A new Pesticide Management Bill has been pending for years and has not replaced the 1968 Act.
• Resistance management: rotate IRAC mode-of-action groups, never repeat the same group in consecutive sprays, use label dose (under-dosing selects resistance), avoid ready-mix cocktails, keep refuge areas.
• Safety: read the label and leaflet, wear PPE, spray with the wind at the back, no eating or smoking while spraying, do not blow a blocked nozzle, triple-rinse and puncture empty containers, keep bees safe by avoiding sprays at flowering/foraging hours. Poisoning first aid - atropine for OP/carbamate poisoning, administered by a doctor.

Surveillance, forecasting and advisory system

• Pest surveillance: fixed-plot and roving surveys; pheromone trap catches; light trap data; weather-based forewarning models.
• Institutions: ICAR-NBAIR (Bengaluru) for biocontrol agents and insect identification, ICAR-NCIPM (New Delhi) for IPM and e-pest surveillance, DPPQS Faridabad with 35+ Central Integrated Pest Management Centres, KVKs, state plant protection wings, Kisan Call Centre (1800-180-1551).
• Digital tools: National Pest Surveillance System, Kisan e-Mitra/Kisan Suvidha, mKisan advisories, Plantix-type image diagnosis; drone application has interim CIB&RC/DGCA Standard Operating Procedures with crop-specific approved labels.

Key points

• Insect pest - an insect whose population causes economic loss; status is relative to the crop, place and season.
• EIL vs ETL - EIL is the break-even density; ETL is lower and is the spray trigger.
• GEP - long-term average density; management aims to lower it, not just to kill the current generation.
• Mouthpart-symptom link - chewing gives holes and frass; sucking gives yellowing, curling and honeydew.
• Dead heart vs white ear - stem borer damage in vegetative vs reproductive stage of rice.
• Hopperburn - circular patches of dried rice caused by brown planthopper; aggravated by excess N and pyrethroids.
• Resurgence - a pest rebounding above pre-spray levels after natural enemies are killed.
• Pest resistance - heritable decrease in susceptibility; managed by rotating IRAC groups and using label dose.
• Pink bollworm - key cotton pest with field resistance to Bt; managed by timely sowing and strict crop termination.
• Fall armyworm - invasive maize pest in India since 2018; whorl damage with moist frass.
• Trichogramma - egg parasitoid released on tricho-cards; *T. japonicum* for rice borer, *T. chilonis* for cotton and vegetables.
• NPV - a host-specific virus; HaNPV at 250 LE/ha for Helicoverpa, applied in the evening with jaggery.
• Neem/azadirachtin - antifeedant, repellent and growth disruptor; safe to natural enemies.
• Label triangle colours - red, yellow, blue, green in decreasing order of toxicity.
• Insecticides Act, 1968 and Rules, 1971 - CIB&RC registration, label claim, waiting period; label-claim use alone is legal.
• DIP Act, 1914 and PQ Order, 2003 - keep exotic pests such as khapra beetle and new invasives out.
• Safe grain moisture - below roughly 10-12% for cereals; aluminium phosphide fumigation by trained operators only.
• Only Bt cotton is approved for commercial cultivation in India among insect-resistant transgenics.

Formulas and examples

Example 1 - Formulation quantity. Chlorantraniliprole 18.5% SC is recommended at 30 g a.i./ha for rice stem borer on 2.5 ha.

• a.i. needed = 30 × 2.5 = 75 g.
• Formulation = 75 ÷ 0.185 = 405.4 mL (about 162 mL/ha, close to the usual label dose of 150 mL/ha).
• With a knapsack spray volume of 500 L/ha, total water = 500 × 2.5 = 1,250 L (25 tanks of 50 L); add about 16 mL of product per 50-L tank (405.4 ÷ 25 = 16.2 mL).

Example 2 - Spray concentration and dilution. Imidacloprid 17.8% SL is to be sprayed at 0.03% a.i. concentration in 500 L water.

• a.i. needed in the tank = 0.03% of 500 L = 0.0003 × 500,000 g = 150 g.
• Formulation = 150 ÷ 0.178 = 842.7 mL in 500 L, i.e. about 84 mL per 50-L tank.

Example 3 - Abbott's corrected mortality. In a bioassay, 60 of 80 larvae died in the treated batch and 6 of 80 in the untreated control.

• Treated mortality = 60/80 = 75%; control mortality = 6/80 = 7.5%.
• Corrected mortality = (75 − 7.5) ÷ (100 − 7.5) × 100 = 67.5 ÷ 92.5 × 100 = 72.97%, i.e. about 73%.

Example 4 - EIL for gram pod borer. Cost of one spray Rs 1,800/ha; chickpea price Rs 55/kg; each larva destroys 2.5 pods over its life; 1,000 pods weigh 1 kg (so 1 pod ≈ 1 g = 0.001 kg); the insecticide prevents 80% of the injury (K = 0.8).

• Loss per larva = 2.5 pods × 0.001 kg = 0.0025 kg = Rs 0.1375 of produce.
• Value saved per larva = 0.1375 × 0.8 = Rs 0.11.
• EIL = 1,800 ÷ 0.11 = 16,364 larvae/ha. At 3.3 lakh plants/ha this is about 0.05 larva/plant, which is why the field ETL is set at the easily observed level of 1 larva/plant only in high-value or late-stage situations - showing that EIL must always be read with the sampling unit.

Example 5 - Infestation and efficacy. In 20 hills of rice, 45 of 300 tillers showed dead hearts before spraying and 12 of 320 tillers a fortnight after; an unsprayed plot moved from 15% to 24% dead hearts.

• Before = 45/300 = 15%; after = 12/320 = 3.75%.
• Reduction over control = (24 − 3.75) ÷ 24 × 100 = 84.4%.

Where it is used

• Agrochemical companies (Bayer, Syngenta, UPL, Rallis, Dhanuka, Coromandel, PI Industries, Godrej Agrovet) - roles in field development, product/territory management, demonstration trials and label-claim trials.
• State agriculture departments and Plant Protection wings - Agriculture Officer, ADO, Plant Protection Officer; pest surveillance, advisories, pesticide licence inspection, quality sampling under the Insecticides Act, 1968.
• Seed companies and transgenic stewardship - resistance monitoring in Bt cotton, insect-resistance management plans, GEAC-linked compliance.
• Biocontrol and biopesticide industry - mass production of *Trichogramma*, NPV, *Trichoderma*, *Metarhizium*; supplied through KVKs and state biocontrol labs.
• Contract farming, export and food processing - residue and MRL compliance for grapes, chilli, basmati, gherkin and tea exports to the EU and Gulf; pre-harvest interval auditing.
• Warehousing and procurement - FCI and CWC/state warehousing corporations; grain hygiene, prophylactic spray with malathion on walls, fumigation schedules, khapra beetle detection.

Interview questions

• Q: What is the difference between EIL and ETL? A: EIL is the pest density at which the loss equals the cost of control, while ETL is a slightly lower density at which control is actually initiated so that the population never reaches EIL.
• Q: Why should synthetic pyrethroids be avoided against brown planthopper in rice? A: They kill natural enemies such as mirid bugs and spiders and stimulate hopper fecundity, leading to resurgence with higher populations than before spraying.
• Q: How do you distinguish dead heart from white ear head? A: Both are stem borer damage - dead heart is the dried central shoot in the vegetative stage, while white ear head is the empty whitish panicle formed when the borer cuts the stem at the reproductive stage.
• Q: Why has pink bollworm become the key pest of Bt cotton? A: It evolved field resistance to Cry1Ac and Cry2Ab proteins, helped by long-duration cotton, extended season, unofficial seed and poor refuge compliance.
• Q: How is a pheromone trap used for monitoring versus for control? A: For monitoring, about 5 traps/ha record moth catches against a threshold; for mass trapping or mating disruption, 20-40 or more traps/ha are needed to actually suppress mating.
• Q: Which insecticide group would you choose for a concealed stem borer and why? A: A systemic or translaminar product such as chlorantraniliprole or cartap, because contact sprays cannot reach larvae inside the stem; application must also coincide with egg hatching.
• Q: What do the triangle colours on a pesticide label mean? A: Under the Insecticides Rules, 1971 they indicate toxicity - red extremely toxic, yellow highly toxic, blue moderately toxic and green slightly toxic.
• Q: What is waiting period and why does it matter? A: It is the minimum interval between the last spray and harvest that keeps residues within the MRL; ignoring it causes export rejections and FSSAI non-compliance.
• Q: How does Abbott's formula help in a bioassay? A: It corrects observed mortality in the treated plot for natural mortality in the untreated control, so efficacy is not overstated.
• Q: Name an invasive insect pest that entered India recently and how it is managed. A: Fall armyworm (2018, first in Karnataka) - managed with early uniform sowing, whorl application of approved insecticides, *Telenomus remus* and *Trichogramma* release, and intercropping.
• Q: Which insecticide is used for grain fumigation and what is the precaution? A: Aluminium phosphide at about 3 g tablet per tonne in gas-tight conditions, applied only by trained and authorised operators because the released phosphine is lethal and there is no field antidote.
• Q: Why does excess nitrogen increase insect problems? A: Lush, soft, high-amino-acid tissue is more nutritious and attractive to sucking pests and borers, and a dense canopy creates the humid microclimate they prefer.

Common mistakes

• Treating ETL as a fixed number for a crop, instead of a value that changes with crop stage, price, control cost and presence of natural enemies.
• Recommending a stomach poison or Bt for a sucking pest, or a contact spray for a borer already inside the stem.
• Confusing resistance (heritable, genetic) with resurgence (ecological rebound after natural enemies are killed) and with tolerance of the host plant.
• Calculating product quantity from the a.i. dose without dividing by the formulation strength - or dividing by 18.5 instead of 0.185.
• Naming a pest only by its common name in exams; the binomial with family carries the marks (and separating *Amrasca biguttula biguttula* from *Bemisia tabaci* as jassid and whitefly).
• Forgetting the waiting period, label claim and bee safety while answering a "management" question - an unapproved molecule is an illegal recommendation however effective.
• Quoting banned products such as endosulfan, monocrotophos on vegetables or DDT as current recommendations; the banned/restricted list is revised by notification, so verify the current CIB&RC list before advising.

Related topics

Integrated pest management · Plant pathology · Agricultural entomology and insect taxonomy · Weed management and herbicides · Pesticide residues and food safety regulation · Storage and post-harvest technology