ASSIGNMENT ON

UNIT - I

Submitted By,Vaishali Parmar04-2385-2014

Submitted ToDr. D. B. Sisodiya

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CONTENT IntroductionImportance of Host Plant ResistanceHistorical perspectivesAdvantages and Disadvantages of

HPRMechanisms of ResistanceAdaptation of Resistance in Plant to

InsectMorphologicalAnatomicalBiochemical

Assembly of plant species - Gene Pool

Behavior in Relation to Host Plant Factor

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Host plant resistance to insect is a conventional approaches and phenomenon of interrelationship between host plants and affected by environmental factors.

It is considerable progress has been made in identification and utilization of crop germplasm for resistance to insect pests (Smith, 2005).

INTRODUCTION

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Plant resistance defined as the “Relative amount of heritable qualities that influence the ultimately degree of damage done by the insect”.

Painter (1951)

Resistance to insect is the inheritable property that enables a plant to inhibit the growth of insect population or to recover from injury caused by populations that were not inhibited to grow.

Kogan (1982)

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It is important to develop techniques to screen for resistance to insect pest under optimum levels of infestation and under similar environmental conditions.

Techniques to screen for resistance to insect have been developed against some insect species (Smith et al., 1994).

However, there is a need to develop systems for insect rearing, refine the resistance screening techniques, and establish long-term programs to screen and breed for resistance to several insect species that are important crop pests.

However, insect resistant cultivars in desirable agronomic backgrounds have been developed in a few crops only (Panda and Khush, 1995).

Cultivars with multiple resistances to insect pests and diseases will be in greater demand in future for sustainable crop production and this requires a concerned effort from scientists involved in the crop improvement programs worldwide.

IMPORTANCE OF HPR

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HISTORICAL PERSPECTIVE Haven’s (1772) reported for the first time the

phenomenon of host plant resistance to insect. He reported that “Underhill“ variety of wheat to be resist the attack of the Hessian fly, Mayetiola destructor (Say) in New York.

Lindy Ley (1831) reported insect resistance in apple variety “Winter Majetin” resistant to wooly aphid, Eriosoma lanigerum.

American grape resistant to grape Phyloxera vitifoliae, which is caused great damage to wine industry by destroying grape wine yards in France, wine industry about to collapsed. So, European grape vines were successfully grafted on to resistant rootstock to save the French wine industry from Phyloxera vitifoliae.

Parnell (1935) in Africa found only single cotton plant not affected by jassid.

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1. Resistant variety is good tool and ecological safer – not hazardous to environment

2. Specificity - Host specific for example, Hessian fly resistance variety ‘Underhill’

3. A cumulative effect• Multiplication of insect lower because life become longer• Control effect added in every generation the pest

population reduced or increased at lower level

4. Resistance is persistent until it is broken by some factors

5. Harmonious with environment• No any adverse effect in nature/local atmosphere• No pollution

ADVANTAGES

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7. Compatible with other methodsResistance variety - Early/late sowing

- Irrigation/ trace condition- Application of insecticides

8. Keep pest population at low level• Morphological characters• Chemical composition• Remained population more vulnerable with chemical/ natural enemy

9. Number of insecticides application reduced

10. Morphological characters responsible to resistance are helpful to other methods. e.g. Hairy leaves of cotton resistant to jassid population which also retention of insecticides is more on hairy leaf. Ultimately, increase efficacy of insecticides.

• Increase efficacy of bio agent

6. Easy of adoption Mahyco - Bollgourd – MECH 12, 162, 184 and Rashi seed – RCH-II

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1. It takes more periods.2.Can not solve the sudden arising time bound pest

problems3.Development of strains or biotypes of insects

breaking resistance of a variety.4.Conflicted – The resistant character may be

conflicted in some cases, if resistant characters present but gave poor yield. Resistant for one pest due to hairy characters, for other requires smooth leaves. This type of character is conflicted and variety is not useful.

5. Genetic limitation• The characters required for resistance may not be

available in germplasm or may be in other crop plant• Not possible to produce seeds by cross hybriding may

produce sterility• Not able to cross with commercial species.

DISADVANTAGES

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Antixenosis (Non preference) The response of the insect to the

characteristics of the host plant which make it unattractive to the insect for feeding, oviposition or shelter. It may be due to physical nature or chemical composition of such plants.

Antibiosis Adverse effects on the insect life history which

result when the insect uses a resistant variety of the host plant or species for food.

Tolerance The ability of the host plant to withstand the

insect attack and grow satisfactorily inspit of the attack by rapidly repairing the damage or by quick development of new tillers, roots etc. in plant of damaged once.

MECHANISMS OF RESISTANCE

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ADAPTATIONS OF RESISTANCE

MorphologicalAnatomicalBiochemical traits

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A. MORPHOLOGICAL BASES

o The morphological characteristics of a plant which confer resistance to insect pests are….

Trichomes on plant surface Surface waxes Hardness of plant tissues Thickening of cell walls and cutical Colour Shape and size

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TRICHOMES

The epidermis of the plants bears hair like outgrowth called trichomes or hairs.

Found on leaves, shoots and roots of plants. Trichomes occur in several forms, shape and sizes.

The trichomes are…. Glandular trichomes or Nonglandular trichomes.

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Plant trichomes

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TYPES OF TRICHOMES

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Nonglandular trichomes

The nongladular trichomes are known to affect locomotion, attachment, shelters, feeding and survival of insects.

Long hairs not only impede movement, but also prevent the insect from reaching the leaf surface to feed on.

Trichomes have basically three types of effects on insect behavior over the leaf surface:

(1) Simple impedance

(2) Physical trapping by hooked hairs

(3) Stickiness caused by exudates from the glandular trichomes.

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Trichomes which restrict insect mobility on plant surface by entrapping, immobilizing and impaling them thus imparting mechanical resistance.

For example, Adults of whitefly, Bemisia tabaci were found trapped by the glandular hairs on tomato leaves (Kisha, 1984).

In sorghum, high trichomes density on lower surface of leaves prevents movement (Gibson and Maiti, 1983) and penetration (Bapat and Mote, 1982) by larvae of Antherigona soccata.

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It affects feeding, development and survival of insect pests by acting as barrier to normal feeding.

For example, Length and density of hair on the lamina of cotton

leaves are the important characteristics in imparting resistance to cotton jassid, Empoasca devastans (Batra and Gupta, 1970).

Jiang and Guo (1996) reported that density of hairiness affected the feeding behavior of cotton aphid, Aphis gossypii.

It inhibit oviposition of various insect pest species on different crop plants.

For example, In okra, Amrasca biguttula population decreased

with an increased in hair density on lamina and such varieties were less preferred for oviposition (Singh, 1987)

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Smith et al (1975) showed that the rate of travel by the first-instar larvae of the pink bollworm Pectinophora gossypiella was more than six times faster on smooth leaves the an on those with pubescence. Because of this lack of movement, the larvae were deterred from the plant substrate.

Hooked trichomes in French bean offer resistance, to aphid, Aphis craccivora

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Glandular trichomes

Glandular trichomes are secrete chemicals which are toxic to insect. Glandular trichomes are generally found in dicotyledonous angiosperm.

A number of plants of the Solanum lycopersicon, Nicotiana and Medicago spp, are particularly adept in producing sticky leaf exudates.

In certain wild potato species (Solanum polyadtnium,, S. berthaultii, and S. tariyense), an exudate is discharged from the four-lobed head of the glandular hairs when aphids Myzus persicac or Macrosiphum euphorbiae mechanically rupture the cell wall (Gibson 1971).

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Polyphenoloxidase and peroxidase activities are exhibited by the glandular trichomes of S. berthaultii for oxidation of the phenolic compounds in glandular exudates (Ryan et al 1982).

Glandular trichomes exudates contain several chemicals which are toxic to the insects.

Trichomes exudates from the leaves of Nicotiana and Petunia species are highly toxic to the leaves to tobacco hornworm, Manduca sexta. It exudates contain large variety of non-volatiles such as alkaloids and phenolics and volatiles such as terpene oils and other essential oils, which act as insect repellents in plants.

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However, in some instances trichomes have been reported to favour incidence of insect pests by providing suitable place for egg lying and by interfering in the activity of natural enemies.

Some insect pests also developed effective morphological, biochemical and other adaptations to neutralize the effect of trichomes.

For example,

Whitefly, Bamisia tabaci preferred to oviposite on hairy varieties. Moths of Leucinodes orbonalis preferred to lay significantly large number of eggs on cultivars having sparse pubescent leaves than on dense pubescent varieties.

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Glandular Plant Trichomes

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SURFACE WAXES Surface waxes over the epicuticle protect the plant

surface against desiccation, insect feeding and diseases.

Epicuticular waxes affect the feeding behavior of insects, particularly the settling of probing insects, acting as phagostimulants or feeding deterrents.

Waxes are esters formed by a linkage of a long chain fatty acids and an aliphatic alcohol.

Due to presence of these waxes on plant surface, the sense organs on the insect tarsi and mouth parts receive negative chemical and tactile stimuli from the plant surface resulting in resistance of the plant to insect pest attack.

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For example, Larvae of Plutella xylostella had non-preference

for leaf wax characteristics in glossy-leaved resistant Brassica oleracea L. (Eigenbrode and Shelton, 1990).

In sorghum, epicuticular wax from younger plants was found more deterrent to Locusta migratoria migratoroides (Reiche and Fairmaire) (Atkin and Hamilton, 1982).

o Wax bloom on leaves of crucifers deter feeding by diamond back moth.

o In onion glossy foliage provide more resistance to thrips.

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COLOUR Genetic manipulation of plant colour usually has an

effect on some fundamental physical plant processes. Certain colors are less attractive to certain insects.

For example, Imported cabbage worm is less attracted to red colored while,

purple foliage and apetalous flowers were resistant to development of Lipaphis erysimi in Brassica species (cabbages, broccoli, and related species).

Cucumber beetles do less damage on reddish colored varieties of leaf lettuce and are attracted to certain hues of yellow.

Harris and Miller (1983) reported that onion fly, Delia antiqua preferred to lay eggs around yellow onion stems.

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THICKENING OF CELL WALLS AND CUTICAL

Toughness and thickness of various plant parts adversely affected penetration and feeding by insects.

For example, In chickpea resistance to bruchid, Callosobruchus maculates is

associated with roughness and toughness of the seed coat (Singal and Singh, 1985).

In sugarcane, varieties with very strong hard mid-ribs in their leaves were found resistant to sugarcane top borer, Scirpophaga nivella as compared to those with weak mid-ribs (Isaac, 1939; Adlakha, 1964).

Thick cortex in the stem of wild tomato, L. hirsutum prevented aphid, M. euphorbiae from reaching vascular tissue - (Quiros et al., 1977).

Rice varieties containing thicker hypodermal layers offer resistance to stem borer.

Stem density of pith and node tissues in wheat resists damage by the wheat stem fly.

Sorgham varieties resistant to shootfly due to the thickness of the cell walls.

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SHAPE AND SIZE Plant shape and size is also known to bring

some behavioural changes in insects while, it is impossible to generalize what shapes resist predation better, shape does play a role in avoiding predation.

For example, Thick rooted turnips were less damaged by turnip

maggots. Another example is in onion with leaves having narrowed angles of contact are more attractive to thrips than onion varieties with looser leaves.

Pod damage due to Helicoverpa armigera was positively correlated with pod circumference, pod length, pod weight and seed weight in chickpea (Gururaj et al., 1993).

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Variations in plant structures also contribute toward insect resistance.

For example, Corn with very tight husks is somewhat resistant

to corn ear worm. Corn varieties with tough, resilient stalks can tolerate burrowing by corn borers with breaking and causing yield loss.

A variety of wheat with a solid stem does not allow sawfly larvae to bore through the stems and reach their feeding sites.

In sugarcane, low number of stomata per unit area has been associated with the resistance characters of varieties to sugarcane scale, Melanaspis glomerata (Agarwal, 1969).

B. ANATOMICAL ADAPTATION

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The biochemical bases of resistance can be divided into two broad categories,

Behavioral responses Physiological responses of insects.

Insect behaviour modifying chemicals are further divided into attractants, arrestants, stimulants, repellents and deterrents,

While plant chemicals affecting the physiological processes of insects may be classified as nutrients, physiological inhibitors and toxicants (Hsiao, 1969).

C. BIOCHEMICAL BASIS

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The types of chemical responsible for insect resistance are numerous but the major classes include the terpenoids, flavonoids, quinones, alkaloids and the glucosinolates.

These are all secondary metabolites, chemicals that are not required for the general growth and maintenance of the plant but which serve as plant defence products.

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The organic isothiocyanates (mustard oils) are the main biologically active catabolites from the glucosinolate components of crucifers, which like other glucosinolates defend plants against generalized insects including aphids and grasshoppers (Panda and Khush, 1995) but can also act as phagostimulants and as kairomonos, crucifer specific hosts (e.g. Dawson et al., 1993).

Some primary and intermediate metabolites such as citric acid and cysteine can also act in plant defence chemistry (Jager et al., 1996).

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There are a number of examples of plant chemicals that have been used in promoting resistance to insects.

Oxygenated tetracyclic triterpenes commonly called cucurbitacins, have been shown to provide antixenotic resistance against Luperini beetles in cucurbits.

Gossypol is a polyphenolic yellow pig ment of cotton plants that has been shown to confer antibiotic resistance to H. zea and H. virescens (Kumar. 1984). o Experiment has shown that the gossypol content of cotton

buds can be increased genetically from a normal 0.5% to 1.5%, and a larval mortality of 50% can be expected when cotton square gossypol content is increased above 1.2% (Schuster, 1980).

o The combination of a high bud gossypol with glabrous cotton strains can result in as much as a 60-80% reduction in Helicoverpa zea and Heliothis virescens larval populations (Lukefahr et al., 1975; Niles, 1980).

ASSEMBLY OF PLANT SPECIES THROUGH

GENE POOL

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Gene Pool: is the set of all genes or genetic information, in any population, usually of a particular species.

Genetic manipulation of crop plants and the introduction of novel genes for resistances (e.g. from bacteria, viruses or unrelated plants) could markedly improve levels of resistance obtained and in some cases reduce the time and cost of more con ventional methods.Germplasm collections consists of,

• Wild species• Weed races• Landraces• Unimproved or purified cultivars no longer in

cultivation• Improve modern cultivars under cultivation • Breeding stocks developed by breeders but not

released for cultivation• Mutants developed by mutagenic treatments as

well as those of spontaneous origin.

Genetic resources can be classified into three gene pool categories :

PrimarySecondary Tertiary

On the basis of difficulty or ease of hybridization and gene introgression (Harlan and De Wet, 1971).

o The primary gene pool consists of improved and unimproved varieties, land and weed races and wild species that readily hybridize with the cultivated germplasm, produce viable hybrids and have chromosomes that pair and recombine allowing genetic exchange. Breeders generally works with the primary gene pool as gene transfer from one background to another can readily be made.

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o The secondary gene pool consists of wild species that are difficult to cross with cultivated forms because of ploidy differences or other barriers (Stebbins, 1958). They have homologous chromosomes that pair poorly with the chromosomes of cultivated species and thus show extremely limited recombination. Thus gene transfer from the secondary gene pools is difficult and time consuming and breeders shy away from using them.

o The tertiary gene pool consists of even more distantly related species belonging to a different subgenus or related genera and even more difficult to hybridize, fertile progenies are rarely obtained. Thus, gene transfer to cultivated species is almost impossible.

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1. Oviposition behaviour Biophysical traits and Biochemical traits

2. Feeding behaviour Visual response Biophysical response Protection response Chemical response Feeding stimulants

BEHVIOUR IN RELATION TO HOST PLANT FACTORS

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Oviposition behaviour Resistance to oviposition may come from plant

characteristics that either fall to provide appropriate oviposition-inducing stimuli or provide ovipositional inhibiting stimuli.

Oviposition preference is discussed on two

bases of the plant’s 1. Biophysical traits

o Plant pubescenceo Frego bracto Visual factors

2. Biochemical traits

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PLANT PUBESCENCE Insects with piercing and sucking mouth parts are

deterred from feeding on hairy plants or vascular bundles.

Breeding of hairy cottons in Africa and Asia to combat the Jassids Empoasca spp. constitutes the foremost host plant resistance (HPR).

Pargell et al., (1949) demonstrated that greater hairiness to both upland cotton (Gossypium hirsutum) and Egyptian cotton (G. barbadense) mm related to jassid resistance.

Soybean varieties with a dense hairiness of foliage can manifest both antixenosis to oviposition and feeding deterrence against leafhoppers, The simple trichomes deter oviposition and feeding by preventing; the insect’s ovipositor or proboscis from reaching the plant epidermis(Lee 1983)

Pubescent wheat cultivar Vel exhibits antixenosis to adults and larvae of the Hessian fly Mayetiola destructor (Roberts et al., 1979).

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FREGO BRACT Other morphological features of plants, such as frego bract

in cotton, help reduce the number of eggs laid and subsequent damage by boll weevils Anthonomus grandis (Jenkins and Parrot 1971).

In field experiments, frego-bract cotton showed 50% less damage from oviposition than normal cottons did. The role of the frego bract in reducing damage by the boll weevil appears to be due to some adverse effect on insect behavior.

Frego bract is associated with hypersensitivity to the plant bugs Lygus spp. and cotton fleahopper Pseudatomoscelis seriatus (Jenkins et al 1973).

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VISUAL FACTORS The colour and shape of plants remotely affect host

selection behaviour of phytophagous insects and have been associated with some resistance.

Ex: Specific color-related resistance, For example, the red and glossy nature of Cruciferae plants was a major factor conferring antixenosis resistance against the cabbage aphid Brevicoryne brassicae (Singh and Bills 1993).

Yellow colour is preferred by aphids.

Green and blue green is preferred by cabbage butterfly.

Dark green preferred by rice leaf folder.

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BIOCHEMICAL FACTORS

Chemical cues are involved in all the three phases of host selection behavior; orientation, oviposition and feeding. Many factors play a role in the process of opposition by different insects, but long-range orientation of many insects to their host plants is known to be guided by volatile, compounds emanating from plants. Volatile hydrocarbons and other secondary compounds act as oviposition deterrents.

Onion volatile diallyl disulfide is antagonistic to onion fly Delia antiqua..

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Feeding behaviour

• Plant resistance to feeding involves nutritional aspects may be expressed by

1. Lack of nutritional support2. The presence of feeding deterrents in host

plants.

Resistance mechanisms directed against insect feeding is usually classified as:

Visual response Biophysical response Protection response Chemical response Feeding stimulants

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Visual response

Colour of host may cause the insect to discriminate between preferred and non preferred host. Resistance due to colour it might be due to different two parameters like wave length and the intensity.

For example, Phytophagous insects may show preference for a specific

fint (colour shade) or specific intensity of colour in their preferred host. Mealy plum aphid after leaving the plum during summer may a light. On the Phramitis communis in response to unsaturated green colour of leaves than on beet plants which bear a saturated green colour.

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Biophysical Response Morphological and anatomical characteristics definitely affect the

utilizability of a plant as host as well as act with other factors. For example,

Long tight husk of corn varieties relatively resistance to the Heliothis and was not increased the larval cannibalism due to prolong entrapping in the husk. Anatomical characters like hard wood stems with closely packed tough vascular bundles making larval entry and feeding difficult conflict resistance.

In sorghum, all resistant varieties were characterized by a distinct lignifcation and thickness of cell wall enclosing the vascular bundle sheaths within the central whorl of young leaves. The resistant varieties of sorghum passes much greater density of silica at the base of first, second and third leaf sheath . The density increased from first to third leaf sheath.

Brinjal shoot borer resistant varieties consist compact vascular bundle in thick layer and low pith area.

Rice resistant varieties- sheath tightly wrapped around the stem.

The leaf minor in brinjal, the tissue surrounding the wound (mines) dry off quickly.

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Protection Response Many thrips species show peculiar behaviour of

seeking protection in narrow crevices on their hosts and remain there securely sheltered for most of the time.

Flowers and grasses with dense inflorescence provide protection from exposure and desiccation as well as supply nutrients to these interstitial dwellers, particularly the larvae.

Dense inflorescence of composites is preferred by many species and a single head of field thistle have over 100 thrips.

Umbeliferae are heavy infested by many thrips. Here quality of food is less important to these thrips than safe housing offered by the dense inflorescence.

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Chemical response

Several chemical constituents of plants sever as olfactory (smell) and gustatory (taste) stimuli.

They may be nutrients e.g. sugars, amino acids etc. or non – nutritive e.g. glucosides, alkaloids, terpenoids etc. These are regarded as preference – non preference response of insects to plants.

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Feeding stimulants

Biting cause maintenance of feeding process once feeding start. e.g. In European corn borer – sugars (sucrose and fructose) act as feeding stimulant.

Some amino acids viz., L-alanine, L-serine, L-arginine act as a stimulant.

Both sugar and amino acids have additive effects on maintainace of feeding in insects like corn borer and grass hoppers.

Kalode and Pant (1967) reported that the most susceptible sorghum variety to Chilo partellus was “Babush” had additional spots of aspertic acid and histidine / argenine as compared to amino acid present in less susceptible “Sundhia” variety.

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