Spodoptera frugiperda (Lepidoptera: Noctuidae) is a major pest of cereal cultures and has become a severe threat in the last few years due to its fast word-wide invasion from its natural range in the Americas. Since then, a major effort is made to control this pest infestation in corn fields, preferably by limiting the usage of chemical pesticides that can promote the emergence of resistant strains. Biological control could be a more sustainable solution, by the use of entomopathogenic agents such as insect specific viruses, parasitoids or entomopathogenic nematodes. However, the targeted caterpillars can mount a powerful and specific immune response against these agents. Understanding the mechanistic details of the insect immune system can provide insight into th ecological parameters of its success. To this effect, we assembled a reference genome for this pest and thoroughly annotated the immunome of S. frugiperda. This allowed us to investigate the transcriptional response, at different time-points and immune tissues of S. frugiperda caterpillars infested with different biological agents. We described that, in the case of the nemato-bacterial complexe Steinernema carpocapsae/Xenorhabdus nematophila, the caterpillar can mount a rapid response against each member of the complex, even though ultimately succumbing to the pathogen. In the process, we identified new actors of immunity that are specific of noctuidae and have been acquired by horizontal gene transfer from bacteria and we are investigating whether they are new antmicrobial effectors or if they participate in the specifity of the response. Finally, we are also investigating the molecular basis of immune priming against nematodes bactérial symbionts.