Researches on herbivory insect saliva in recent years have revealed that insect salivary components play important roles in relationships and coevolution between insects and plants. A variety of enzymes and organic components in saliva of herbivory insects can induce series of biochemical responses in damaged plants which could be very specific to species or even to larval instars of the feeding insects. It has been demonstrated that enzymes, such as  β-glucosidase, glucose oxidase, etc., and organic chemicals, such as volicitin, can trigger induced defense responses in plants. However, there have been no direct evidences that salivary components of piercing_sucking insects play roles in induced plant chemical defenses even though plants also responded to feeding by these insects. Salivary components of herbivory insects are variable with host plant species most likely due to biochemical or physiological adaptation of insects to nutrients and toxins in different plants. Insect protein analyses indicated that similar salivary components were found in insects with the same types of mouth parts and similar food resources. Researches in salivary components of herbivory insects may elucidate mechanisms in insect-plant coevolution, formation of insect biotypes, outbreaks and damage of insect pests， and may also have significance in guiding insect pest management.