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.

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

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.

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.

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.

I full agree with Luis Miguel Constantino .

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.

Plants can defend themselves, morphigically and biochemicals inside plants.

By means of plant conditioning. Sprays such as Bordeaux mixture induce poisoning of plant sap that is toxic to insects, which might be due to induced physiological change of the plant caused by the chemical substance.

By bringing some morphological and biochemical changes, plants defend themselves from insects.

Excellent research work. I wish to be further informed about such bio active compounds from succulent plants

Plants defend themselves from insects by the phyto-chemicals present in their body may be phenols, alkaloids, or toxic organic chemicals .These chemicals tact as insect repellents due to toxic characters.Lot of information available on insect plant interactions.

Md. Nur Alam Miah

Certain chemicals produced by plants are able to keep insects and pests away from them. Please have a look at this book.

https://www.sciencedirect.com/book/9780128193044/natural-remedies-for-pest-disease-and-weed-control