Abstract:

Insect oral secretion (OS), also known as vomit, is a mixture of saliva secreted by salivary glands and secretions secreted by guts in insects. During insect feeding on host plants, OS is secreted into plants and affects plant defense responses. RNA interference (RNAi) is a valuable reverse genetics tool to study insect gene function and also a new technology to be used in pest control. In this article, we mainly reviewed the effects of insect OS on host plant defense, the identification of insect OS effectors and the feasibility and application of OS effectors based on RNAi technology in pest control. Insect OS affects host plant defense mainly by interfering with jasmonic acid signalingpathway, sieve tube obstruction, and  Ca²⁺ pathway and other defense responses in host plants, and then promotes insects to ingest food. At present, the main methods of identification of insect OS effectors are based on the transcriptomic analysis of insect salivary glands and proteomic analysis of OS. Most of the OS effectors have been identified from insects with sucking mouthparts, and less reported in insects with chewing mouthparts. The functional studies revealed that the expression of insect OS effectors in host plants can affect the survival rate, fecundity, and feeding ability of insects and other important physiological indexes of both insects and plants. By identifying the interaction between OS effectors and plant defense mechanisms, the roles of OS effectors in the relationship between insects and host plants have been further demonstrated. Based on RNAi technology, the expression levels of OS effector genes are downregulated, and the growth and development are affected in many insects by microinjection-, feeding-, and plant-mediated RNAi using OS effector genes as targets, suggesting that OS effector genes could be used as RNAi targets. Although the studies are still in the laboratory stage, their application in pest control has been proven to be feasible in certain degree. Insect oral secretions are a new direction to study the interaction mechanism between insects and host plants. Finally, the future research directions of OS have been prospected, hoping toprovide some theoretical guidance for studies of pest control in China.

Key words: Insect, oral secretion, host plant, effector, RNA interference, pest control