Insect immunity has gradually attracted broad attention in recent years because of its important physiological functions in the process of insect resistance to harmful exogenous stimuli.Although both internal and external immunity are parts of the insect immune defense system,it is generally believed that the internal immunity is an immediate and primary immune response of insects while the external immune defense is only considered as a kind of secondary immune response.Nevertheless,the external immunity using defensive secretions as the core component constitutes the first barrier to foreign substances which invade insects.Accordingly,external immunity and internal immunity are two kinds of immune defense strategies for insects.When insects suffer exotic organism infection or adverse environmental factors,the external immunity is often the priority to be employed to fight against the invasion of natural enemies or adversity.However,the internal immunity and external immunity are both synchronized in the whole process of defense,which will cause a dilemma on energy allocation between the two defense strategies.Moreover,it is essential for insects to employ a series of immune reactions to prevent potential threats,which will seriously impair the effectiveness of pest biological control.This review focuses on insect external immunity and summarizes the current understandings on defensive secretions in insects,as well as the two immune defense strategies and their trade-offs,aiming to provide a synthesis of important updates,potential applications,and novel ideas and technologies for further research in this area.Also,the related research will not only contribute to further analysis about the immune interaction and diversified immunization strategies between insects and exogenous factors to improve the control effect in the field,but also pave the way for the development of novel insecticides targeting the insect immune system.%昆虫免疫在昆虫抵御有害外源刺激的过程中具有重要的生理调控作用,因而近年来受到了广泛关注.虽然体内免疫和体外免疫皆为昆虫免疫防御系统的组成部分,但是传统观点普遍认为,体内免疫是昆虫迅速和主要的免疫反应,而体外免疫防御仅仅被认为是一种次要的免疫响应.然而,以分泌防御物为核心的体外免疫却构成了外源异物入侵昆虫的第一道防线.因此,体外免疫和体内免疫是昆虫的两种免疫防御策略.当昆虫遭受外来生物入侵或外界不良环境因子影响时,为了抵御天敌或抵抗逆境,它们将优先选择体外免疫防御策略.但是,昆虫在整个防卫过程中,体内免疫和体外免疫却是同步进行的,这将涉及到两种免疫防御策略之间的能量分配问题.同时,当昆虫受到外源物入侵时,必然启动一系列的免疫响应来阻止潜在的威胁,这将严重影响到害虫生物控制的效果.本文以昆虫体外免疫为焦点,就昆虫防御分泌物、两种免疫防御策略及其权衡进行综述,旨在了解昆虫防御分泌物及体内体外免疫权衡的研究现状和重要作用,深入剖析昆虫和外源因子的免疫互作效应和多样化的免疫防御策略,为促进该领域的发展和开发以昆虫免疫系统为靶标的新型杀虫剂提供新的思路和方法.
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