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Unique CFP (cysteine-free protein; 120 aa) has been identified as an extraordinary virulence factor in <i>Beauveria bassiana</i> (Cordycipitaceae), a main source of wide-spectrum fungal insecticides. Its homologs exclusively exist in wide-spectrum insect pathogens of Hypocreales, suggesting their importance for a fungal insect-pathogenic lifestyle. In this study, all three CFP homologs (CFP1–3, 128–145 aa) were proven essential virulence factors in <i>Metarhizium robertsii</i> (Clavicipitaceae). Despite limited effects on asexual cycles in vitro, knockout mutants of <i>cfp1,</i><i>cfp2</i> and <i>cfp3</i> were severely compromised in their capability for normal cuticle infection, in which most tested <i>Galleria mellonella</i> larvae survived. The blocked cuticle infection concurred with reduced secretion of extracellular enzymes, including Pr1 proteases required cuticle penetration. Cuticle-bypassing infection by intrahemocoel injection of ~250 conidia per larva resulted in a greater reduction in virulence in the mutant of <i>cfp1</i> (82%) than of <i>cfp2</i> (21%) or <i>cfp3</i> (25%) versus the parental wild-type. Transcriptomic analysis revealed dysregulation of 604 genes (up/down ratio: 251:353) in the Δ<i>cfp1</i> mutant. Many of them were involved in virulence-related cellular processes and events aside from 154 functionally unknown genes (up/down ratio: 56:98). These results reinforce the essential roles of small CFP homologs in hypocrealean fungal adaptation to insect-pathogenic lifestyle and their exploitability for the genetic improvement of fungal insecticidal activity.