Assalam

This is a extensive discussion.

Insects are beneficial for plants as pollination, But herbivorous insect caused damage on plant, so plant try for defense against Herbivorous. for example "Indirect Defense" cause attract of natural enemies(Predators and Parasitoids) of Herbivorous Insect by Production of more nectar flowers.

The Best Regards

S.Mahmoudvand

There is a primary and secondary metabolic compounds

Soit directement par exemple un pin lorsqu'il est attaqué par un insecte il excrete la résine poyr noyer ce dernier.

Indirectement un arbre feuillus par rapport un insecte défoliateur ce n'est que l'année prochaine qu'il va produire des feuilles de moindre qualité avec beaucoup de fibre.

Assalam

This is a extensive discussion.

Insects are beneficial for plants as pollination, But herbivorous insect caused damage on plant, so plant try for defense against Herbivorous. for example "Indirect Defense" cause attract of natural enemies(Predators and Parasitoids) of Herbivorous Insect by Production of more nectar flowers.

The Best Regards

S.Mahmoudvand

May be through production of inset replant materials to keep it away from plant parts.

Interesting! Following answers.

Hi Md. Nur Alam Miah

The papers attached adds more information. Check them out.

Thanks all of you for nice answer, suggestions and link. Best wishes for all.

Some species of plants have thorns, others have poisons that are produced as a secondary metabolites while others folds off their leaves.

Plants can defend themselves from insect pests by several approaches .Of these morphological aspects by having setae which render crawling of insects on the surface of the plant or the can make good barrier between the insect and the plant . Plant can produce some materials such as gum.In addition,plants are able to defend themselves by using secondary substances such as alkaloids ,steroids and flavelinoids. Salam and best wishes .

Thank you Mr. Tawfiq for your nice and informative response.

Thank you and you are always welcome Dr Miah .

This question may raise extensive discussion. Here are some information that may help the understanding of plant defense against herbivory:

Plants are evolutionary armed against herbivores. They produce a large array of chemical compounds (e.g., Eugenol in clove plants) which may have strong insecticidal activities (killing or repelling) against insect pests. Furthermore, plants have other strategies as the production of physical barriers (e.g., trichomes) or the recruitment of biological control agents via the emission of volatile compounds mediated by herbivory.

Physical Defenses: Plants possess a variety of adaptations to overcome insect attack, and some of these are physical characteristics that reduce a plants attractiveness or nutritive value. Physical defensive adaptations are associated with plant color, surface waxes, pubescence, trichomes, specialized glands and anatomical adaptations involving plant shape and form.

Chemical Defense: Many species of green plants possess secondary metabolic products, chemicals that are not involved in primary metabolism. In some case plant reproduction increases in response to herbivory, while in other instances reproduction decreases under pressure from herbivores. Plant chemical defenses are generally categorized as quantitative or qualitative.

Quantitative defense: Tannins, resins and essential oils are effective against nearly all herbivores.

Qualitative defenses: Cyanogenic glycosides, glucosinolates, various nonprotein amino acids, and peptides are effective against a more limited variety of herbivores.

In plant resistance to insects there are two important terms that you should know:

Non-preference (anti-xenosis)

Host plants that express non-preference affect the way an insect pest perceives the desirability of the host plant. Non-preference plants either provide stimuli that are unattractive to the pest (color, odor, texture such as downy hairs) or fail to provide stimuli that are attractive to the pest. In this way, non-preference plants affect the behavior of pests.

Antibiosis resistance affects the biology of the insect so pest abundance and subsequent damage is reduced compared to that which would have occurred if the insect was on a susceptible crop variety. Antibiosis resistance often results in increased mortality or reduced longevity and reproduction of the insect.

Nice and fruitful scientific discussion

Please look at the following link, it is useful:

https://www.apsnet.org/edcenter/disimpactmngmnt/topc/Pages/OverviewOfPlantDiseases.aspx

The mechanisms of defense of plants against insect are: Presence of secondary metabolite toxic for insects; induction of specific enzymes, lectines and others directed against the insects; secretion of toxic substances from broken trichomas at the surface of leaves; emission of series of volatile chemicals attracting the parasitoids; synthesis of repellent substances; physical barriers…

To defend themselves against herbivory, plants are thought to have developed a broad arsenal of morphological and chemical adaptations. These adaptations can be divided into direct and indirect defenses. Direct defenses, by definition, have a direct negative impact on herbivores and include thorns, spines (urticating), hairs and trichomes, sclerotizations, waxes, canal secretions (latex, resins), and a great diversity of secondary plant metabolites. Indirect defenses, on the other hand, refer to plant characteristics which attract and support the natural enemies of herbivores, whose predatory and parasitic potential can provide indirect protection to plants. Plant attributes which have been interpreted to represent such indirect defenses include nutritional rewards, such as extrafloral nectar and food bodies, domatia (morphological adaptations which serve ants or other predators as shelter and nesting sites) and herbivory induced plant volatiles (used by predators and parasitoids to locate feeding herbivores). See also https://www.researchgate.net/publication/33682661_Recruitment_of_predators_and_parasitoids_by_herbivore-injured_plants

Please go through the following RG link.

Article Mechanisms of Plant Defense against Insect Herbivores

The plant can defend itself in several by: 1) physical ways, such as the formation of tissues or structures that impede the insect. 2) chemical methods by a signaling system that stimulates the production of insect repellent terpentenes, non-desirable chemical compounds of the insect such as the production of some glycosidic or phenolic compounds or the production of toxic compounds such as alkaloids compounds.

Plants can defend themselves from insect pests by several approaches .Of these morphological aspects by having setae which render crawling of insects on the surface of the plant or the can make good barrier between the insect and the plant . Plant can produce some materials such as gum.In addition,plants are able to defend themselves by using secondary substances such as alkaloids ,steroids and flavelinoids

Primary barriers - Dark and waxy cuticles, or adaptations, such as thorns and spines, to protect them from pathogens.

In case of failure of primary barriers, secondary metabolites (toxic compounds) such as glycol cyanide, harm the pathogen.

Plants also produce antimicrobial chemicals, antimicrobial proteins, and antimicrobial enzymes to fight the pathogens.

Morphologically and physiologically .For more details see above .

I full agree with Luis Miguel Constantino .

Crop plants show three types of resistance mechanism against insect-pests attack in the context of their functional relationship:

1. Non-preference or Antixenosis: Non-preference is an insect response when the host plant is unattractive for insect feeding, oviposition and shelter. As 'non-preference' seems more of an insect character, it was later named as 'Antixenosis' which means 'against the guest'. Here, some plants are unattractive to insect either due to absence of desirable characters or the presence of undesirable characters. Eg: Hairy varieties in cotton are not preferred by leafhoppers for

oviposition, Open panicle of sorghum supports less Helicoverpa armigera.

2. Antibiosis: This is the adverse effect of host plant on the insect due to the presence of some toxic substances or deficiencies of required nutritional components. The adverse effects may be reduced fecundity, reduced sizesize, long life cycle, failure to pupate or failure of adult emergence, and increased mortality. Indirectly, antibiosis may result in increased exposure of the insect to its natural enemies.

Eg: The most classical example of host plant resistance is DIMBOA content in maize which imparts chemical defence against the European corn borer Ostrinia nubilalis. Some nutritionally deficient varieties (less in aspargine content) of rice in India results in under-developed ovaries in the brown planthopper, Nilaparvata lugens female 3.Tolerance: Plant can also withstand the damage done by insect-pests by promoting its growth. for ex: producing more number of tillers, roots, leaves etc in the place of damaged plant parts. Tolerance usually results from general vigour of the plant, regrowth of the damaged tissues, production of additive branches, efficient utilization of non-vital plant parts by the insect and compensation by the growth of neighbouring plants

Eg: Early attack by shoot fly in sorghum induced the production of a few synchronous tillers that grow rapidly and survive to produce the harvestable product.

Md. Nur Alam Miah

My response was mostly covered by Gaurav Singh. However, in addition to examples of non-preference, plants may produce thick cortex that makes it difficult for the larvae to penetrate or tunnel. Example in sweetpotato varieties providing resistance against sweetpotato weevils.