miR-8 modulates immune defense and growth in Arma chinensis Fallou: Implications for pathogen resistance and...

Arma chinensis Fallou is a critical biocontrol agent for agricultural pests; nevertheless, its effectiveness is limited by susceptibility to pathogens. The development of artificial diets is anticipated to address this challenge, necessitating a systematic investigation into the physiological and molecular regulatory mechanisms underlying immunity and developmental processes in A. chinensis. This approach further requires the identification of genes and regulatory molecules critical for maintaining immune homeostasis and developmental progression in this species. Using RNAi technology, paraffin sectioning, HE staining, and metabolomic sequencing, the regulatory mechanisms of miR-8 on the immunity and growth of the natural enemy insect A. chinensis were revealed at multiple levels, including individual, cellular, molecular, and metabolic levels. A. chinensis resistance to viral infection by activating innate immunity pathways while enhancing antimicrobial peptide AchDefensin production. Meanwhile, host miR-8 can inhibit the proliferation of AcMNPV. Metabolomic profiling revealed miR-8's systemic influence on bile acid biosynthesis, actin cytoskeleton dynamics, and insulin secretion, which coordinate nutrient utilisation and growth via mTOR and IIS signalling. Overexpression of miR-8 significantly increased host body size, shortened developmental time, and promoted fat body expansion. This study reveals miR-8 as a pivotal regulator of A. chinensis immunity and development, presenting innovative options to improve the cost-effectiveness of biological control. These findings enhance the comprehension of miRNA-mediated pathogen resistance in beneficial insects, with ramifications for sustainable pest management and invertebrate disease control.