AimsWe report the first occurrence of an epizootic of the ascomycete fungus, Isaria tenuipes (teleomorph Cordyceps takaomontana), on the ocola skipper Panoquina ocola (Lepidoptera: Hesperiidae), an insect pest affecting rice in Brazil. Methods and ResultsField surveys in flooded rice fields in the state of Goias in Brazil were conducted, and a fungal pathogen of a caterpillar pest (P. ocola) was serendipitously found. This fungus inflicted high infection levels (average 862%) mainly to the pupal stage during warm, humid growing conditions. Typically, mycosed pupal cadavers produced milky-white to pale yellow synnemata bearing an average of 1102x10(9) conidia per cadaver. Based on phylogenetic analysis using beta-tubulin gene sequences, we confirmed that all 12 isolates obtained from field-mummified pupae were identifiable as I. tenuipes. ConclusionsOur data expand our knowledge on the host and geographical ranges of this mycopathogen and underscore its epizootic potential to affect a lepidopterous insect pest on rice in Brazil. This finding may facilitate the exploitation of this fungus as a mycoinsecticide. Significance and Impact of the StudyIsaria tenuipes may be used as an effective and environmentally friendly bioinsecticide against agricultural caterpillar pests due to its epizootic potential, as well as explored for medicinal purposes by pharmaceutical industry.