The present invention relates to mutants of a parent Trichoderma strain, comprising a polynucleotide encoding a polypeptide and one or more genes selected from the group consisting of a peptaibol synthetase gene, a paracelsin synthetase gene, a first terpene cyclase gene, a second terpene cyclase gene, and a third terpene cyclase gene, wherein one or more of the genes are modified rendering the mutant strain deficient in the production of one or more of the enzymes selected from the group consisting of a peptaibol synthetase, a paracelsin synthetase, a first terpene cyclase, a second terpene cyclase, and a third terpene cyclase compared to the parent Trichoderma strain when cultivated under identical conditions. The present invention also relates to methods of producing a polypeptide in such mutants and methods for producing such mutants.