🐛 Botanical Pesticides

This lesson builds core elective concepts in BSc Agriculture with practical applications and exam-oriented clarity.

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Botanical Pesticides

Botanical pesticides are naturally occurring chemicals (secondary metabolites) extracted from plants that possess insecticidal, fungicidal, or repellent properties. They have been used in traditional agriculture for centuries and are gaining renewed importance in organic and sustainable farming systems.

Neem — Azadirachta indica

Neem is the most important botanical pesticide worldwide. The key active compound is azadirachtin, a complex tetranortriterpenoid concentrated primarily in neem seeds (kernel contains 0.2-0.8% azadirachtin).

Modes of Action

• Antifeedant — disrupts feeding behaviour, causing insects to starve
• Insect growth regulator (IGR) — interferes with ecdysone synthesis, disrupting moulting
• Oviposition deterrent — reduces egg-laying by adult females
• Repellent — drives pests away from treated surfaces
• Sterilant — causes ovarian malformation and reduces fecundity

Neem-Based Products

Product	Active Ingredient	Recommended Dose
Neem Seed Kernel Extract (NSKE)	Azadirachtin (crude)	5% suspension (50 g kernel/litre)
Neem oil	Azadirachtin + other limonoids	2-3 ml/litre
Commercial formulations	Azadirachtin 0.15-5% EC	1-2 ml/litre as per label

Neem products are effective against over 400 insect species including aphids, whiteflies, leaf miners, bollworms, and stored grain pests. They are also active against certain nematodes and fungal pathogens.

Pyrethrum

Pyrethrum is extracted from the dried flower heads of Chrysanthemum cinerariaefolium (now Tanacetum cinerariaefolium), primarily grown in Kenya, Tanzania, and Rwanda. The active compounds are six esters collectively called pyrethrins (pyrethrin I and II, cinerin I and II, jasmolin I and II).

Properties

• Rapid knockdown effect — fast-acting neurotoxin that blocks sodium channels
• Low mammalian toxicity (LD50 oral: 1200-1500 mg/kg in rats)
• Photolabile — degrades rapidly in sunlight (low environmental persistence)
• Synergised with piperonyl butoxide (PBO) to inhibit detoxification enzymes in insects

Pyrethrum is widely used in household insecticides, grain storage, and organic crop protection.

Rotenone

Rotenone is an isoflavonoid extracted from roots of Derris elliptica and Lonchocarpus species. It acts as a mitochondrial electron transport chain inhibitor (blocks Complex I), affecting cellular respiration in insects and fish. Due to concerns over toxicity to aquatic organisms, its use has been restricted or banned in several countries, though it remains approved in some organic farming programmes.

Essential Oils

Several plant essential oils show promising pesticidal activity:

• Citronella oil (Cymbopogon nardus) — mosquito repellent
• Eucalyptus oil — fumigant against stored grain pests
• Clove oil (eugenol) — fungicidal and insecticidal
• Pongamia oil (karanja) — effective against mites and sucking pests

Botanical pesticides are valued for their rapid biodegradability, low residue levels, and compatibility with organic certification standards, making them essential tools in residue-free agriculture.

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Summary Cheat Sheet

Topic	Key takeaway
Main focus	Botanical Pesticides — Neem (azadirachtin), Pyrethrum, Rotenone, essential oils, and their role in sustainable crop protection.
Section context	Revise this lesson with the rest of Biopesticides and Biofertilizers for stronger conceptual continuity.