Molecular immune responses of male locusts Locusta migratoria to an Aspergillus oryzae XJ1 infection

Background Many fungal pathogens infect and kill host insects successfully through the suppression of host immune systems, making them potential biological control agents. Aspergillus oryzae is a new fungal pathogen of locust Locusta migratoria , which is an important insect pest worldwide; consequently, information on the molecular mechanisms that it uses to suppress the host's immune system is limited. Here, transcriptomic analyses of male locusts during an A. oryzae infection were used to characterize the temporal variations in the host's molecular immune responses. Results Two key immune tissues, fat body cells and hemocytes, exhibited distinct functional roles in the locust's defense against Aspergillus infection, with their contributions varying over time. Following A. oryzae infection, the expression of pattern recognition receptors ( PRRs ) increased in fat body cells but decreased in hemocytes. In fat body cells, the expression of serine protease inhibitors ( SERPINs ) showed a significant increase at 48 h and 72 h postinfection (hpi) with A. oryzae . In hemocytes, SERPINs exhibited an initial upregulation at 24 hpi, followed by a downregulation by 72 hpi, suggesting that serine proteinase activity is suppressed, which in turn hinders the activation of downstream pathways such as prophenoloxidase (PPO), peroxidase (POD) and Toll pathways. Most effectors, such as lysozymes, defensins and peroxiredoxin, were upregulated in fat body cells by 48 hpi. PPOs were down‐regulated both in fat body cells and hemocytes. Conclusions The findings revealed that A. oryzae infection markedly weakened the locust's immune defenses within 72 hpi, resulting in a reduced host's Toll pathway in response to the fungal pathogen infection. These results offer critical information that can be utilized to design highly efficient biocontrol in integrated locust management programs with microbial agents.