Abstract: Recent researches of piercing-sucking insect saliva have revealed that salivary components play important roles in relationships between piercing-sucking insects and plants. For most piercing-sucking insects, they will secrete gell saliva and watery saliva when they feed on plants. The gell saliva will be secreted at the early stage of feeding to form salivary sheath, which is supposed to surround and protect the stylet. This saliva can help piercing-sucking insects to feed on plants directly and indirectly. Meanwhile, the watery saliva contain s many components like pectnase, cellulose, polyphenol oxidase, peroxidase, alkaline phosphatase, sucrase, etc .These components can help piercing-sucking insects in plant tissue penetration, food digestion, detoxification of plant secondary substances and break down of plant defence reaction. Paradoxically, salivary components can also trigger defence reaction of plants. They can either elicit pl ant wounding messengers to trigger the direct defence reaction or elicit the production of plant volatiles to attract carnivorous natural enemies. Many piercing-sucking insects can cause plant pathological reaction differentially and some researches assumed that piercing-sucking insect salivary enzymes, such as polygalacturonase, alkaline phosphatase, sucrase, polyphenol oxidase, etc ., might be responsible for that. However, there have been no direct evidences for these hypot heses. Moreover, the amino acids and proteinase in piercing-sucking insect saliva are responsible for gall-forming of plants. It has been demonstrated that piercing-sucking insects can change salivary components to adapt different host plant species and meet different physiological requirements. Researches in salivary components of piercing-sucking insects may elucidate mechanisms in outbreaks, damages and virus transmission of piercing-sucking insect pests and piercing-sucking  insect-plant coevolution, and may also have significance in guiding insect pest management.

Key words: Piercing-sucking insects, salivary components, plant induced reaction, coevolution, host plants, effective pest management