Abstract: The innate immunity of insects includes cellular immunity and hurmoral immunity. Recent studies have shown that 20-hydroxyecdysone (20E), one of the key hormones in the regulation of insect growth and development, is involved in the regulation of insect innate immunity. In this article we focus on the molecular mechanisms of 20E regulating the innate immunity in insects and the influence of microorganisms on 20E titer based on the mechanisms of insect immunity. 20E can activate cellular and humoral immunity against invasive microorganisms, and the stimulation of exogenous microorganisms can promote the increase of 20E titer by 3-dehydroecdysteroid-3β-reductase (3DE-3β-reductase). 20E has a significant effect on the immune system of insects, and the increase of its titer can activate cellular immunity, including phagocytosis, encapsulation and nodulation, while the effect on humoral immunity is more complex. Besides accelerating melanization, whether 20E promotes or inhibits the expression of antimicrobial peptides is not clear yet. Researchers identified a number of key genes through which 20E regulates humoral immunity, and they can be grouped into three categories according to the pathways they are involved in: the first is dependent on innate immune pathways such as Toll and IMD, the second is dependent on insulin signaling pathways, and the third is the direct regulation by 20E signaling pathway via such transcription factors as BR-C. However, the way these pathway factors interact with each other and their molecular regulatory mechanisms are still unclear and deserve further study.

Key words: Insect, -hydroxyecdysone')">20-hydroxyecdysone, innate immunity, cellular immunity, hormoral immunity, molecular mechanisms