12-epi-Hapalindole J isonitrile (1) and three previously described hapalindoles, 12-epi-hapalindole C isonitrile (2), hapalindole L (3) and 12-epi-hapalindole E isonitrile (4) were isolated and identified as insecticidal alkaloids of the biofilm-forming freshwater cyanobacterium Fischerella ATCC 43239 (Stigonematales). The structures of the purified compounds were elucidated by ESI-FTICR-MS, GC-EI-NIS and various 2D NMR experiments. At 26 mu M hapalindole 1 killed 100% of the larvae of the dipteran Chironomus riparius within 48 h. Insecticidal activities were also found at similar concentration for the hapalindoles 2-4. The bioactivity of hapalindoles demonstrates that cyanobacterial biofilms can be considered as promising sources of insecticidal metabolites which might be useful for the biocontrol of dipterans. (C) 2007 Elsevier Ltd. All rights reserved.