Fungal family Entomophthoraceae that are obligate pathogens of insects have massive genomes, some exceeding 1 Gb. They are largely expanded by transposable elements (TEs), but the reason and impact of TE driven genome expansion remains poorly understood. This study investigates TE - mediated genome expansion, active TE families, and the mechanisms of TE silencing in these early diverging fungi. I used Extensive de-novo TE Annotator (EDTA) for de novo TE discovery and characterization in this study. I identified LTR/Ty3 retrotransposons as the primary contributors to genome expansion, with the largest TE families proliferating after species diversification. While Entomophthora muscae exhibits a compartmentalized genome distinct from the classic "two-speed genome" model, no evidence of a RIP-like mutation system for TE silencing was detected for Entomophthoraceae genomes. Notably, two active MITE families and their associated autonomous elements were identified in Entomophaga maimaiga, with insertion preferences near genes consistent with other MITE families. This study provides critical insights into TE-driven genome expansion in Entomophthoraceae, advances our understanding of their evolutionary history, and establishes a framework for characterizing active TEs in early diverging fungi
