This document discusses the role of secondary plant metabolites in insect pest management. Secondary metabolites are compounds produced by plants that are not directly involved in growth or development but play an important role in plant defense. The major groups of secondary metabolites discussed are terpenes, phenolic compounds, sulfur-containing compounds, and nitrogen-containing compounds. Many secondary metabolites have insecticidal, antifeedant, or repellent properties that help protect plants from herbivorous insects and other pests. The document also reviews several plant-derived products that are used commercially in pest management due to their secondary metabolite content.

1. ROLE OF SECONDARY PLANT METABOLITES IN INSECT
PEST MANAGEMENT
SURENDRA SINGH SHEKHAWAT
M.SC. (AG.) PLANT PROTECTION
GI – 9048

2.  A primary metabolite directly involved in :-
Physiological function in the organism such as
Normal growth, development and reproduction
For example :-
1.Carbohydrates 2. Proteins
4. Nucleic acids
3. Lipids
5. Hormones
Primary metabolites
Introduction

3. They directly not involved in the normal growth, development and reproduction of an
organism.
Play an important role in plant defense against insect herbivory and avoid infection by
microbial pathogens.
 Major groups :-
Secondary Metabolites
1. Terpenes
2. Phenolic, flavonoids and polyphenolic compounds
3. Nitrogen-containing alkaloids and sulfur-containing compounds

4. Secondary metabolites are derived from primary
metabolites

5. Major sub-classes
Terpenes
• Monoterpenes
(C10)
• Sesquiterpenes
(C15)
• Diterpenes
(C20)
• Triterpenes
(C30)
• Polyterpenes
(C5)n
Phenolic
compounds
• Coumarin
• Furano-
coumarins
• Ligin
• Flavonoids
• Isoflavonoids
• Tanins
Sulphur containing
secondary
metabolites
• GSH
• GSL
• Phytoalexins
• Defensins,
thionins and
lectins
Nitrogen containing
secondary
metabolites
• Alkaloids
• Cyanogenic
glucosides
• Non-protein
amino acids

6. 1. Terpenes
Toxic & feeding deterrents eg. Acetyl-coA or glycolytic intermediates
This is mixture of essential oil which include volatile compounds, limonene and menthol
Lends characteristic odor to their foliage
Found in glandular hairs that projected out from epidermis
They stored in modified extracellular space in cell wall
Types of Terpenes
1. Monoterpenes
2. Diterpenes
3. Sesquiterpenes
4. Triterpenes
5. Polyterpenes Fig : Menthol

7. Show strong insecticidal responses to insects.
Popular ingredient in commercial insecticides.
• Examples:-
Pyrethroids occur in the leaves and flowers of
chrysanthemum.
Gymnosperms (conifers) - pine and fir.
Resin ducts found in the needles, twings and
trunk.
• Cucurbitacin in cucurbits.
i. Monoterpenes

8. Abietic acid is found in pines and leguminous plants.
It Present in or along with resins in resin canals.
When these canals are pierced by feeding insects, The
outflow of resin may physically block feeding and
It serve as a chemical deterrent to continued predation.
Cannabis plant against predators like insects and animals.
iii. Sesquiterpenes
Antiherbivore agents of family compositae
Strong feeding repellence to many herbivorous insects
Fig. Cannabis plant
Fig. Sunflower
ii. Diterpenes

9. iv. Triterpenes
Milkweeds produce glucosides (sterols)
Limnoid in citrus fruits and act as antiherbivore compounds in members of family rutaceae.
Azadirachtin, a complex limnoid from Azadirachta indica, acts as a feeding deterrent to
some insects and exerts various toxic effects.
Fig. Milkweed CitrusNeem leaf

10. V. Polyterpenes
Larger terpenes include the tetraterpenes and the polyterpenes.
Principal tetraterpenes are carotenoids family of pigments.
Rubber found in long vessels called laticifers, provide protection as a mechanism for wound
healing and as a defense against herbivores.
Rubber treeFig. Carrot

11. 2. Phenolic compounds
Plants produce a large variety of secondary products that contain a phenol group.
Important part of the plants defense system against insect pests.
i. Coumarin
 Simple phenolic compounds, widespread in vascular plants and appear to function in
different capacities in various plant defense mechanisms against insect herbivores and fungi.
 Derived from Shikimic acid pathway.
 Cyclic compounds behave as natural pesticidal defense compounds for plants.
ii. Lignin
 Highly branched polymer of phenyl-propanoid groups.
 Physical toughness deters feeding by herbivorous animals and its chemical durability makes
it relatively indigestible to herbivores and insects.

12. iii. Flavonoids
Perform very different functions in plant system including pigmentation and defense.
Plant phenols constitute one of the most common and widespread group of defensive
compounds, which play a major role in HPR against herbivores, Including insects
iv. Isoflavonoids
 Isoflavonoids are derived from a flavonone intermediate, naringenin.
 play a critical role in plant developmental and defense response.
 Secreted by the legumes and play an important role in promoting the formation of nitrogen-
fixing nodules by symbiotic rhizobia.
v. Tanins
 It included under the second category of plant phenolic polymers with defensive properties.
 Tannins are general toxins that significantly reduce the growth and survivorship of many
herbivores and also act as feeding repellents to a great diversity of animals.

13. 3. Sulphur containing secondary metabolites
 They Constitute major chemical defenses in the brassicaceae, alliaceae and asteraceae.
I. GSH (Glutathione) is rapidly accumulated after fungal attack, may act as systemic
messenger carrying information concerning the attack to non-infested tissues.
II. GSL leading to formation of an unstable intermediates, i.e. Isothiocyanates (RN=C=S)
and nitriles function in defense as herbivore toxins and feeding repellents.
• Phytoalexins are synthesized in response to bacterial or fungal infection. Antimicrobial
metabolite in rice (Oryza sativa L.) Leaves.

14. IV. Defensins, thionins and lectins
S-rich non-storage plant proteins.
Involved in the natural defense system of plants.
Highly toxic to micro organisms, insects and mammals.
Some plant species produce lectins as defensive proteins that bind to carbohydrate or
carbohydrate containing proteins.
After being ingested by herbivores, lectins bind to epithelial cell lining of the digestive
tracts and interfere with nutrient absorption.

15. 4. Nitrogen containing secondary metabolites
Include alkaloids.
Cyanogenic glucosides.
Non protein amino acids.
Most of them are Biosynthesized from common amino acids.
All are of considerable interest because of their role in the anti herbivore defense and
toxicity to humans.

16. i. Alkaloids
Found in more than 15,000 compounds and 20% of vascular plants
Alkaloids-heterocyclic ring with N and C atoms
Fig. Different Alkaloids

17. ii. Cyanogenic glucosides
Constitute a group of n-containing protective compounds other than alkaloids, release
the poison HCN
Usually occur in members of families viz.,Graminae, Rosaceae and Leguminosae.
They are not in themselves toxic but are readily broken down to give off volatile
poisonous substances like HCN and H2S.
When the plant is crushed, their presence deters feeding by insects and other
herbivores such as snails and slugs.
Limabean (Phaseolus lunatus l.) Is a model plant for studies of inducible indirect anti
herbivore defences.

18. Fig. Examples of Cyanogenic glycosides

19. iii. Non-protein amino acids
• Incorporated into proteins but are present as free forms and act as protective
defensive substances.
• For examples, canavanine and azetidine-2-carboxylic acid are close analogs of
arginine and proline respectively.
• After ingestion, canavanine is recognized by herbivore enzyme that normally binds
arginine to the arginine transfer RNA molecule and so become incorporated in to
proteins in place of arginine

20. Role of SM in insect pest management
Development of agriculture has been due to the use of synthetic pesticides to
reduce the losses caused by pests.
 At the same time, some of these products have affected human health.
They have created environmental and pest resistance problems
Solutions to crop protection problems.
The interest in plants and their chemo-biodiversity as a source of bioactive
substances has increased.
Plants are capable of synthesizing an overwhelming variety of small organic
molecules called secondary metabolites.
These subtances have been used for the benefit of mankind for many years as
crop protection agents.
Discovery of new potential bio-pesticides.

21. General aspects and approaches
Plants cannot run away in case of danger and do not have an immune system to
combat pathogens.
Plants have capacity to synthesize an enormous variety of low molecular weight
compounds are secondary metabolites.
Over 2000 plant species are known to have pesticidal properties.
Many of these plants are used by farmers in developing countries.
Plants secondary metabolites may be referred to as plant natural products.
Plant secondary metabolites as natural products: terpenes and terpenoids
(~25,000 types, 55%), alkaloids (~12,000 types, 27%), and phenolic compounds
(~8,000 types, 18%).

22. Semiochemicals
Chemicals emitted by plants, animals, and other organisms that evoke a behavioural or
physiological response in individuals of the same or other species.
They include pheromones and allelochemicals
Allelochemicals are semiochemicals produced by Individuals of one species that modify the
behaviour of Individuals of a different species (i.e., An interspecific Effect).
They include allomones (emitting species Benefits), kairomones (receptor species benefits)
and Synomones (both species benefit).
Pheromones areSemiochemicals produced by individuals of a species That modify the
behaviour of other individuals of the same Species (i.e., An intraspecific effect).

23. Background and present situation of the development and use of
plant metabolites in pest management
The use of pyrethrum and derris species in china as insect control agents.
In early times of agricultural development, such spices as cinnamon, mustard,
nutmeg and pepper were used to protect food from insect attack.
Before the second world war, four main groups of compounds were commonly
used i.e. Nicotine, alkaloids, rotenone and rotenoids, pyrethrum and pyrethrins,
and vegetable oil.
The continuous and massive use of synthetic pesticides has produced several
unexpected side effects, such as acute and chronic toxicity to human.
development of resistance in pests, elimination of natural biocontrol and
pollination agents, insect resurgence, effects on non-target organisms, and
environmental contamination with potential effects on the entire food chain

24. • In bio-pesticide market, the most important is pyrethrum followed by
neem, rotenone and essential oil.
• In USA, it is registered for being use in agricultural, residential,
commercial, industrial, and public health sites.
• Typically used as insecticides (e.g., Pyrethrum, rotenone, rape seed
oil, quassia extract, neem oil, nicotine)
• Repellents e.g. Citronella, fungicides e.g., Laminarine, fennel oil,
lecithine, herbicides.

25. Secondary metabolites in HPR
 Allelochemicals
1. Allomones : benefit to producer, i.e. Host plant
2. Kairomones : beneficial to receiving organism, i.e. Phytophagous insect.
 Allomones are considered to be a major factor of insect resistance in plants
1. DIMBOA (Dihydroxy methyl benzoxazin)- against european corn borer, Ostrinia nubilalis
2. Gossypol (polyphenol) -Helicoverpa armigera (American bollworm)
3. Sinigrin – aphids -Myzus persicae
4. Cucurbitacin -cucurbit fruit flies
5. Salicylic acid -rice stem borer
6. Benzyl alcohol – In barley against greenbug, Schizaphis graminum.

27. Insect Antifeedents in host plants
Plant Feeding deterrents Insect
Cruciferae Sinigrin Pieris brassicae
Cucumis sativus Cucurbitacin Tetranichus urticae
Phyllotreta nemorum
Gossypium spp. Gossypol Heliothis virescens
Spodoptera littoralis
Earis insulana
Isoquercitrin, Quercitrin,
Quercetin
Helicoverpa zea
Pectinophora gossypiella
Hordeum spp. Gramine Schizaphis graminum
Tomato Rutin, chlorogenic acid,
α- tomatine H. Zea
Medicago spp. Coumarin Hypera postica, sitona cylindricollis
Solanaceae Demissine, solacauline Leptinotarsa decemlineata

28. Successful application
Product Botanical Source Main bioactive
Component(s)
Biological effect Mode of
action
Trade name
Pyrethrum Tanacetum
Cinerariaefolium
Pyrethrins I and
II, cinerins I and
II,
jasmolins I and II
Insecticide,
Acaricide
axonic
poisons
Pyganic,
Diatect 5
Neem (neem
Oil)
Azadirachta
Indica
azadirachtin,
dihydroazadiracht
in,
variety of
Triterpenoids
insecticide,
acaricide,
Fungicide
Moulting
inhibitors,
antifeedant/
Repellent
Ecozin,
Azatrol EC,
Agroneem,
TrilogyTM
Nicotine Nicotiana spp. (S)-isomer, (RS)-
isomers, and (S)-
isomer of nicotine
sulfate.
Insecticide neurotoxin
(acetylcholi
ne
agonist)
XL-All
Nicotine,
Tobacco Dust
Sabadilla Schoenocaulon
spp.
mixture of
alkaloids-
cevadine
Insecticide Axonic
poisons
Red Devil, Natural
Guard

29. Successful application
Product Botanical
Source
Main bioactive
Component(s)
Biological effect Mode of action Trade name
Karanjin Derris indica Karanjin insecticide,
Acaricide
antifeedant/repel
lent insect
growth regulator
Derisom
Phenethyl
Propionate
component of
peppermint oil
phenethyl
propionate
insecticide,
insect
Repellent
repellent EcoSmart HC
Citric acid plant-derived
acid
citric acid insecticide,
acaricide,
Fungicide
- SharpShooter,
Repellex
Capsicum
Oleoresin
Capsicum spp. Capsaicin repellent,
fungicide,
Nematicide
Neurotoxic,
repellent
Hot Pepper Wax
jojoba
essential oil
Simmondsia
californica
straight-chain
wax esters
fungicide,
Insecticide
suffocation (eggs
and immature
life stages)
Eco E-Rase,
Permatrol

30. Successful application
Product Botanical
Source
Main bioactive
Component(s)
Biological
effect
Mode of action Trade name
Cinnamon
essential oil
Cinnamomum
Zeylanicum
Cinnamaldehyde Insecticide octopamine
antagonists;
membrane
Disruptors
Weed ZapTM,
Repellex
Lemon grass
essential oil
Cymbopogon
nardus,
Cymbopogon
citratus
citronellal, citral Insecticide octopamine
antagonists;
membrane
Disruptors
GreenMatch
EX
Mint
essential oil
Mentha species
(mint)
Menthol Insecticide octopamine
antagonists;
membrane
Disruptors
-
Citronella oil Cymbopogon
spp.
citronellal,
geraniol,
other terpenes
Repellent

31. Conclusion
In modern agriculture for alternative solutions to plant health problems, the interest
in plants and their chemo-biodiversity as a source of bio-active secondary
metabolites has increased.
Application of these defense strategies in an agricultural setting might offer new
ecofriendly approaches to increase insect resistance in crops
Among the major challenges to be faced by the farmers for products to reach the
market are :-
The sustainable use of raw materials
The standardization of chemically complex extracts, and
The regulatory requirements and approval.
Complexity of volatile blend and large numbers of different herbivore enemies
suggests that many of these defenses remain to be characterized