Defenses of plants against insects The fact that plants and insects have responded to each other through time means that not only have insects gotten better at eating plants, but that plants have developed a variety of resistance factors to deter feeding and damage by insects. The physical factors include those plant structures that interfere with insect movement, feeding, or reproduction associated with that plant. This involves the proliferation of plants tissues or resins which tend to repel the feeding. A solid stem, hard stem, or thick cortex provides resistance. Trichomes are hairlike epidermal outgrowths which occur on leaves, shoots, and roots.
Effectiveness depends on density, erectness, length, and shape.
These represent a wide range of compounds. Also referred to as allomones . These are the most important deterrents that plants have against insect feeding. Terpenoids are nonnitrogenous and based on 5-carbon chains. These are compounds that prevent the successful digestion of proteins by herbivores, generally occur in seeds, tubers, and foliage.