This presentation consists of few data about various morphological, physiological and anatomical adaptation in plant to prevent insect-pest attack. It does not include complete data but can provide a quick reference.

1. Ph.D Research Scholar
Entomology & Agril. Zoology
Banaras Hindu University, Varanasi

2. CONSTITUTIVE
INDUCED
Present in plant species
before
Produced and mobilized
to site of injury
Plant Defense

3. For million of years plants and insects have been
interacting with each other as a food and feeder
relationship. In progress of time, both have evolved
strategies to avoid each other’s defense systems with
adaptation of morphological, physiological, anatomical
and behavioral mechanisms that have either toxic,
repellent or anti-nutritional effects on herbivores.
 Most of insects interact with plants for three basic
reasons: 1- Food/ Nutrition
2- Shelter/ Colonization
3- Reproduction

4. PLANT HERBIVORE
NATURAL
ENEMY
 The plants can defense/ resist herbivores by following
two ways:
I. Directly, by affecting host’s preference, survival and
reproductive success (Intrinsic Plant Defense)
II. Indirectly, through attracting other species such as
natural enemies of the insect (Extrinsic Plant Defense)
Extrinsic Plant Defense
Intrinsic Plant Defense
(Dhaliwal, G.S and Arora, R. (2006). ‘Integrated Pest Management’, Kalyani publisher: p. 119)
attack attack
defense defense

5. ‘Resistance refers to the heritable qualities of a
cultivar to counter act the activities of insects so as to
cause minimum percentage reduction in yield as
compared to other cultivars of same species under
similar condition.’
- Dhaliwal et al. (1993) -
 The mechanisms of resistance can be studied into 3
catagories, viz. antixenosis, antibiosis and tolerance.
 The resistance mechanisms can be greatly affected
by environmental factors like tempetarute, humidity,
photoperiod, soil moisture, soil pH and also by plant
and insect factors.

6. Tolerance:
Ability of the host plant to withstand an insect population
sufficient to damage severely the susceptible plants.
Antixenosis:
Host plant characters responsible for non-preference of the
insects for shelter, oviposition, feeding, etc.
Antibiosis:
Adverse effect of the host plant on the biology (survival,
development and reproduction) of the insects and their
progeny due to the biochemical and biophysical factors
present in it.

7. Various Defense Structures present in plant to resist against
herbivore are listed as below:
a) Trichomes
b) Thorns, spines and prickles
c) Silica content
d) Stem characters: solidness, toughness, thickness
e) Thickening of cell wall and rapid proliferation of plant tissues
f) Surface waxes
g) Color
h) Plant cuticle
i) Plant shape and size
Morphological or physical resistances constituted by interfering:
 locomotive function
 Feeding
 Reproductive functions

8. a) Trichomes (Pubescence)
 These are cellular, hair-like out-growths of the plant epidermis,
which may occur on leaves, shoots, or roots.
 In general functions of trichomes is water conservation but also
provide morphological defense against insects attack.
 These can be, straight, spiral, hooked, branched, or un-
branched and can be glandular or non-glandular.
 Glandular trichomes secrete secondary metabolites including
flavonoids, terpenoids, and alkaloids that can be poisonous,
repellent, or trap insects and other organisms, thus forming a
combination of structural and chemical defense.
 The mechanical effects of trichomes depends on four main
characteristics such as density, erectness, length, shape.

9. (Microscopic view of trichomes)
( Non-glandular vs glandular trichomes )
NGT
GT

10. I. Insect Mobility and Trichomes:
Trichomes interfere insect mobility by Entrapping
Immobilizing or Impaling the insects pest from host. Few
examples are as below :
 Hooked trichomes of bean Phaseolus vulgaris L. impale
aphid Aphis crassivora
 French bean small hooked epidermal hairs affects colonies of
A. Crassivora
 Hairiness in cotton confers resistance against Pectinophora
gossipiella restricting larval movement on leavs.
 Adults of white fly Bemisia tabaci
were found trapped by glandular hairs
on tomato leaves

11. Interlocking of trichomes and tarsi of insect while walking on leaves of a plant

12. II. Insect Feeding Development and Trichomes:
Trichomes affects insect feeding , development and survival.
 Length and density of hair on lamina of cotton and soybean
leaves prevent jassids Empoasca devastans/ fabae
 Hairiness on pods of mung bean affect feeding of
Callosobruchus chinensis
 Rice varieties with hairy upper lamina were found less
susceptible to Asiatic rice borer Chilo suppressalis
III. Oviposition and Trichomes:
 Trichome exudates of Lycopersicon, prevent the oviposition
of H. zea
 Presence of oxalic and malic acids in chickpea trichome
resistant to H. armigera
 Trichomes in okra prevent egg laying in A. bigutula bigutula

13. Thorns are modified branches that protect plants
from grazing vertebrates, and include the honey
locust tree (Gleditsia triacanthos). Many cacti
produce thorn-like structures that are actually
modified leaves or parts of leaves (e.g., stipules)
called spines which serve similar purposes, such
as in the barrel cactus (Ferocactus spp.).
Botanically speaking, the “thorns” on the stem of
rose plants (Rosaspp.) are neither true thorns nor
spines: they are actually outgrowths of the
epidermis called prickles.
b) Thorns and Spines (Spinescence)
THORNS
SPINES

14. b) Silica Content: Silica deposited in plan parts. Character confined to
Graminae, Cyperaceae and Palmaceae. Few examples are :
 Sorghum silica content in 4th and 6th leaf stage less incidence of
shoot fly Atherigonia soccata
 In paddy against asiatic rice borer Chilo suppressalis and
Scirpophaga incertulas
c) Solidness and other stem characters: Mainly thickness and
toughness. Few examples are :
 Rice varieties with small stem and rigid surface against Asiatic rice
borer
 In sugarcane rind hardness against internode borer Chilo
sacchariphagus indicus.
 Rind hardenss in combination with fibre conent against shoot borer
C. Infuscatellus
 Sorghum genotypes with thin and longer stem, fewer but long
internode, short peduncle resistant to stalk borer C. partellus

15. d) Thickness of cell wall: Thickness of wall , hardness of
tissue and rapid proliferation of plant tissue affects penetration
and feeding
Examples:
 Thickness of all categories of veins has positive correlation
between the with egg laying by A. bigutulla bigutulla in
okra, brinjal and cotton.
 Sugarcane varieties with strong midrib are resistance to top
borer Scirpophaga nivella
 In chick pea resistance to bruchid, Calobruchus maculatus
is associated with toughness of seed coat
Susceptible Resistance
Bruchid
attack

16. e) Surface Waxes:
 The first line of defense in plants is an intact slippery bark and
a waxy cuticle.
 Protect plant surface from desiccation, diseases, affect feeding
behaviour of insect by lack of probing, phagostimulant or
feeding deterrants. Few examples are :
 Glossy leaved brassica oleriaceae not prefered by larvae of
Plutella xylostella.
 Glossy lines of Brassica species has low population of
cabbage worm, cabbage aphid and diamond back moth .
 Along with herbivore defense, wax helps to keep water in
the plant and reduce transpiration.

19. f) Colour:
Exist naturally in leaves, petals, fruits, stem etc and also
can be conferred by genetic modification. Few examples are :
 Cotton cultivars with red leaves less attacked by boll weevil
 Red foliaged Brassica species less attacked by white flies
compared to green foliaged
 Mustard aphid prefer to alight to yellow colour of petals
Colours preferred by Insects:
- Aphid, White fly, Leaf hoppers
Green & Bluish green- Cabbage butterfly
Dark green- Rice leaf hopper

20. R
R
R
S
S
S
R- Resistance
S- Susceptible
COTTON
MUSTARD
CABBAGE

21. g) Plant Cuticle: Consist wax , pectin, and cellulose. Affects feeding
and oviposition behavior. Few examples are :
i) Larve of Helicoverpa zea prefered to feed on older leaves of
soybean over younger one throughout season
ii) Potato leafhopper Emposca fabae preferred to oviposit on newest
part of the plant over elder tissue
iii)Younger leaves of lemon are preferred for probing, oviposition and
survival by barberry whitefly, Parabemisia myricae over mature
leaves.
h) Shape and size: Known to bring some behavioral changes
Examples:
i) Sorghum cultivar with shorter glumes and shorter floral structure
resistance to earhead midge Contarinia sorghicola
ii) In chickpea pod damage due to H. armigera is positively correlated
with pod circumference, pod length, pod weight

22. Variations in plant structures also provide resistance to
some extent. Examples:
 Rice varieties with tight leaf sheath wrapping : Asiatic
rice borer
 Awned spring wheat: Sitobion avenea (Aphid)
 Corn silk balling : Corn earworm H. zea
 leaf glossiness, plumule and leaf sheath pigmentation :
shoot fly Atherigona soccata in sorghum
 Trees such as coconut and other palms, may protect
their fruit by multiple layers of armor.

23.  In corn, silk balling is associated with
resistance to corn earworm, H. zea, as silk
ball appears to present a physical barrier to
ear penetration.
 In sugarcane, low number of stomata per
unit area has been associated with the
resistance character of varieties to sugarcane
scale Melanaspis glomerata (Green)
 Clones with loose-fitting leaf sheaths are
generally more damaged by the intemode
borer, Chilo sacchariphagus indicus.

24. Plant physio-chemicals can be divided into :
 Primary metabolites are substances produced by all plant
cells that are directly involved in growth, development, or
reproduction (sugars, proteins, amino acids, and nucleic acids )
 Secondary metabolites are organic compounds not directly
involved in growth or reproduction but they are often involved
with plant defense.
 Secondary metabolites are often characterized as
either qualitative or quantitative.

25. Secondary Metabolites
QUALITATIVE
METABOLITES
Qualitative metabolites
are toxins that interfere with
an herbivore’s metabolism,
often by blocking specific
biochemical reactions.
- present in plants in
relatively low concentrations
(often less than 2% dry
weight)
QUANTITATIVE
METABOLITES
Most quantitative
metabolites are digestibility
reducers that make plant cell
walls indigestible to
herbivores.
- present in high
concentration in plants
(5 – 40% dry weight)

26. List of available secondary metabolites in plants :
 Cyanogenic glycosides
 Glucosinolates
 Benzoxazinoids
 Terpenoids or isoprenoids- Monoterpenes, diterpenes,
triterpenoids.
 Phenolics- tannins, flavonoids, lignin, Furanocoumarins,
silymarin and cannabinoids etc.
 Nitrogen Compounds- Alkaloids (Caffeine, Nicotine, .
caffeine, morphine, cocaine, colchicine etc)
 Cyanogenic glycosides
 Plant defensive proteins
 Coumarins

27.  Cyanogenic glycosides are stored in inactive forms in
plant vacuoles. They become toxic when herbivores eat the plant
and break cell membranes allowing the glycosides to come into
contact with enzymes in the cytoplasm releasing hydrogen
cyanide which blocks cellular respiration.
 Glucosinolates are activated in much the same way as
cyanogenic glucosides, and the products can
cause gastroenteritis, salivation, diarrhea, and irritation of the
mouth.
 Benzoxazinoids, secondary metabolites, which are characteristic
for grasses (Poaceae), are also stored as inactive glucosides in
the plant vacuole. Upon tissue disruption they get into contact
with β-glucosidases from the chloroplasts, which enzymatically
release the toxins.

28.  These are derived from various amino acids. Over 3000
known alkaloids exist; few examples are-
include nicotine, caffeine, morphine, cocaine, colchicine,
ergolines, strychnine, and quinine.
 Certain alkaloids bind to nucleic acids and can inhibit
synthesis of proteins and affect DNA repair mechanisms.
 Alkaloids can also affect cell membrane and cytoskeletal
structure causing the cells to weaken, collapse, or leak,
and can affect nerve transmission.
ALKALOIDS

29. PLANT PHENOLICS:
They are produced primarily via the shikimic acid and
malonic acid pathways in plants, and include a wide variety of
defense-related compounds including flavonoids, anthocyanins,
phytoalexins, tannins, lignin, and furanocoumarins.
 Flavonoids are one of the largest classes of phenolics.
Mostly isoflavonoids protect the plant against insect pests by
influencing the behavior, and growth and development of
insects.
 Tannins are water-soluble, produced by plants and stored in
vacuoles. Tannins are toxic to insects because they bind to
salivary proteins and digestive enzymes including trypsin and
chymotrypsin resulting in protein inactivation.

30. PLANT DEFENSIVE PROTEINS AND ENZYMES
 Many plants and seeds contain proteins that specifically
inhibit pathogen and pest enzymes by forming complexes
that block active sites or alter enzyme conformations, which
ultimately reducing enzyme function.
 They include defensins, amylase inhibitors,
lectins, chitinases, lysozymes and proteinase inhibitors etc .
 Insect attack induces various plant protiens due alteration of
gene expression under stress, which play an important role in
signal transduction, and oxidative defense.
 Cry 1 protein or Bt- protein is best example of defensive
proteins, but these come under induced genetic
adaptations

33. INSECT HORMONE MIMICS AND ANTAGONISTS
 Many insect hormones are known, two powerful hormones,
the juvenile hormone (JH) and the ecdysone or moulting
hormone (MH) are recognized to play a major role in these
processes.
 It is presumed that plants may have developed juvenoids
and ecdysteroids (analogues of these hormones) as subtute
for defenses against insect pests.
 Farnesol, seasamin, juvabione, sterculic acid and thujic
acid are some of the important juvenoids isolated from
plants and are known to disturb normal metamorphosis,
moulting and reproductive process of insects (Bowers
W.S., 1991).

34.  Natural products posessing a 5,6-benz-2-pyrone
skeleton are called coumarins.
 The coumarins may be variously hydroxylated,
alkylated, alkoxylated or acylated, which exert a
tremendous effects on the herbivorous insects.
 Coumarins can deter feeding as well as interfere with
development of insects.
e.g. The simple coumarin ‘bergamottin’ is ovicidal to
Leptinotarsa decemlineata (Say) and ‘mammein’ toxic to
mustard beetles.
COUMARINS

35. The nutritional requirements of insects are similar to other
animals, and any imbalance in digestion and utilization of plant
proteins by the insects’ results in drastic effects on insect
physiology.
 DIMBOA in Corn: Prevent Southern corn borer
 Less quantity of asparagine in Rice: Decrease BPH fecundity
 Low amino acid and high sugar in Pea: Resistance to pea aphid
 High gossypol content in Cotton: Resistance to bollworms
 High saponin content in Potato: Resistance to cut worms

36. INDIRECT DEFENSES
 The mechanism by which the plant defenses itself by
enhancing the probability of attracting the natural enemies of
herbivores.
 Such an arrangement is known as mutualism.
 When a plant is attacked it releases allelochemicals and
volatile organic compounds (VOPs) may be allomones or
kairomones, which attracted the predators towards the
damaged plant, and feed on herbivores.
 Plants also provide housing and food items for natural
enemies of herbivores
For example: The tree Macaranga have adapted their thin stem
walls to create ideal housing for an ant species.
 Most plant use of endophytic fungi in defense is well known.

37. Indirect defenses function by (a) attracting predators such as ants, wasps, and mites
including food rewards or chemical signals advertising the presence of prey. (b)
Once present, predators attack and/or remove herbivores that can damage the plant
(c) direct defenses, do not require a mediator to negatively affect herbivores.
(d) Decreased feeding by herbivores results in less damage to the plant.

38. Depending on the herbivore’s physical characteristics
(i.e. size, feeding behaviour and defensive armor),
structural defenses varies from plant to plant and
insects to insects.
Plant adaptations to a particular insect pest may take
long time and so the chemically induced resistance
can be a better way to prevent the pests.
Instead of direct defense we can go for enhancing
indirect defense of plant by releasing bio-control
agents to crop ecosystem.

39.  https://en.wikipedia.org
 http://www.nature.com/scitable/knowledge/library/plant-
resistance-against-herbivory
 Juvik, J. A. and Babka, B. A. (1988). Journal of Chemical
Ecology, Vol.-14, No. 4
 Yoshida, M. et al. (1997). Journal of Chemical Ecology, Vol.-23,
No. 4
 Google Images
 Dhaliwal, G.S and Arora, R. (2006). ‘Integrated Pest
Management’, Kalyani publisher: p. 119
 Panda, N. and Khush, G. S. (1995). Host plant resistance to
Insect, CAB International, UK,.pp. 420.
 Ram, P. , Singh, R. and Dhaliwal, G. S. (2004). Biophysiacal
Bases of Resistance in plants to insects; Host Plant Resistance to
Insect: Concepts and Applications eds., Panima Publishing
corporation, New Delhi pp. 94-97.