Computational Tools and Lessons Learned from Annotating Transposable Elements in Insect Genomes

Transposable elements (TEs) are mobile, repeated DNA sequences whose evolutionary relationships with host genomes span the full spectrum from parasitism to mutualism. Within Insecta, one of the most species-rich animal groups, TE content and family richness vary dramatically, yet annotation efforts have historically concentrated on Drosophila, leaving roughly half of non-drosophilid insect TEs classified as unknown. Insect genomes thus represent a vast, largely untapped reservoir of TE diversity. This review guides newcomers through the annotation of TEs in insect genomes, clarifying what can and cannot be achieved with automatic versus manually curated TE libraries. We outline the two core stages of modern annotation: de novo discovery of a representative repeat library, comparing the strategies of popular and emerging tools, followed by genome-wide annotation. We critically examine TE classification, including the promise and current limitations of machine-learning classifiers, and detail best practices for quality control and redundancy reduction. We argue that annotation depth should be dictated by the biological question rather than pursued exhaustively, and we survey both manual curation tools and recent automated curation pipelines. Finally, we address the shift toward pangenomic approaches and the evolving TE database landscape, along with the importance of depositing libraries in versioned, open repositories.