Study On Density-dependent Larval Body-color Morphs Differentiation And Mechanism Of Spodoptera Exigua

Body-color morph differentiation exists in many insects have,among which population density plays an important role in the regulation of insect body-color morph differentiation.At present,many studies have been conducted on the density-dependent phases differentiation of locusts.However,there are controversies on whether insects closely related to agroforestry production have similar regulatory mechanisms,and how the density regulates insect body color change through upstream signals is still unclear.This study was conducted on beet armyworm larvae with four aspects: the phenomenon and regular pattern of body-color morph differentiation,density regulation of body-color morph differentiation,regulation signal pathway of density-dependent body-color morph differentiation,and density-dependent body-color morph differentiation and immune defense.The main results are as follows:1.Phenomenon and regular pattern of body-color morph differentiation of beet armyworm larvaeTheresults of body-color morph differentiation survey of beet armyworm larvae in field and indoor body-color morph differentiation observation of beet armyworm larvae showed that there was body-color morph differentiation among beet armyworm larvae,which occurred in the 4th and 5th instar larvae,and was most obvious in the 5th instar larvae,It’s melanized type of 5th instar larvae had obvious darkening on dorsomeson and the upper spiracle line,with a darker dorsal color.2.Density regulation of body-color morph differentiation of beet armyworm larvaeThe results of processing different rearing densities of beet armyworm larvae and screening of key signals show that the body-color morph differentiation of beet armyworm larvae is density-dependent,and the 3rd instar larvae are most sensitive to rearing density,which is density-sensitive stage;tactile stimulation is the key signal for the densitydependent body-color morph differentiation in larvae.3.Regulatory signaling pathways for density-dependent body-color morph differentiation in beet armyworm larvaeThe results of the RAN-seq analysis of the beet armyworm larvae showed that bodycolor morph differentiation of larvae induced by tactile stimulation and high-density rearing have great similarity in gene expression level.Signaling pathways such as "ECM-receptor interaction" may be key signaling pathways involved in density-dependent body-color morph differentiation of beet armyworm larvae.4.Density-dependent body-color morph differentiation and immune defense of beet armyworm larvaeThe results of a comparative analysis of the immune defense of beet armyworm larvae showed that melanized individuals caused by tactile stimulation had similar level of immune defenses to those melanized individuals caused by high density,and that the melanized type of beet armyworm larvae may have higher immune defense level than the green type of larvae.In summary,this study clarified the phenomenon and the regular pattern of body-color morph differentiation in beet armyworm larvae.It was found that larval body-color morph differentiation was density-dependent,and tactile stimulus signals were involved in this process.The molecular mechanism of density regulating body-color morph differentiation and effect of density on larval immune response were explored.This study revealed the role of tactile stimulus signals in density-dependent body-color morph differentiation in insects,and layed a foundation for exploring the regulatory mechanism of insect body-color morph differentiation and analyzing the link between insect body-color morph differentiation and immune response.