Toxicity of culture filtrate and fungal mat from sixty five strains of fungi to silkworm larvae, Bombyx mori L., has been evaluated by feeding test. The 3 rd instar of the larvae were fed on an artificial diet containing each sample to be tested at 25°C for 6 days.
Twenty four strains in test fungi showed oral toxicity. A toxic component isolated from Arthrinium spp., Penicillium cyclopium and Penicillium puberulum was identified as β-nitropropionic acid.