Abstract:  Herbivorous insects and host plants have developed complicated defense and counter defense mechanisms through co-evolution. In this article, we systematically reviewed the roles of insect saliva effectors and elicitors in the interactions between insects and plants and their mechanisms. The salivary elicitors secreted by insects during feeding can be recognized by plants to trigger early plant immunity, while insect effectors released from oral secretion can inhibit plant immune defenses. Resistant plants further evolved R proteins to recognize insect avirulence effectors and initiate effector-triggered immunity. Phytophagous insects can avoid the recognition by plant R proteins through different strategies. Therefore, in this arms race, insect saliva determines whether insects can succeed to feed on plants. During feeding process, chewing insects secrete a large number of enzymes into plants, and piercing-sucking insects secrete sheath saliva and water saliva into plants, but both of them utilize effectors and elicitors to manipulate plant immune responses. By analyzing the reported insect effectors, it was found that the molecular mechanisms of insect effectors are different. They affect plant early defense signals, regulate plant hormone pathways or others, or target small RNA pathways. Recent advances in insect elicitors were also reviewed in this article, revealing that elicitors can induce the release of plant secondary metabolites, and regulate hormone levels, Ca²⁺ influx and reactive oxygen species (ROS) burst to enhance plant resistance. Finally, we analyzed the secretory characteristics, host specificity and multifunctionality of insect effectors, and discussed research prospects on avirulence effectors and their plant R genes as well as pattern recognition receptors of elicitors. 

Key words: Insect effectors, insect elicitors, plant immune defense responses, piercing-sucking insects, chewing insects