The present invention relates to methods for reducing or eliminating the expression of a target gene in a filamentous fungal strain, comprising: (a) inserting into the genome of the filamentous fungal strain a double-stranded transcribable nucleic acid construct comprising a first nucleotide sequence comprising a promoter operably linked to a homologous coding region of the target gene and a second nucleotide sequence comprising the homologous coding region, or a portion thereof, of the target gene, wherein the first and second nucleotide sequences are complementary to each other and the second nucleotide sequence is in reverse orientation relative to the first nucleotide sequence; and (b) inducing production of an interfering RNA encoded by the double-stranded transcribable nucleic acid construct by cultivating the filamentous fungal strain under conditions conducive for production of the interfering RNA; wherein the interfering RNA interacts with RNA transcripts of the target gene to reduce or eliminate expression of the target gene. The present invention also relates to the filamentous fungal strains and to methods of producing a biological substance of interest in such filamentous fungal strains.