Swarms of non-biting midges (Diptera:Chironomidae) became a serious nuisance in central Israel beginning in the spring of 1998. The source of these midges was 200 hectares of ponds in the Dan Region Waste Stabilization Ponds (DRWSP) plant. DRWSP is the central waste treatment and water recycling facility for 1.5 million residents in Israel’s largest urban center, Tel-Aviv, and vicinity. Recently, a mechanical-biological treatment plant facility was built to replace the oxidation ponds. In 1998, only 5% of raw sewage was treated in oxidation ponds, changing the water quality to that conducive for midge population outbreaks of a magnitude not previously observed at this site (Broza etal., 2000). Midges became a severe nuisance in the adjacent town, mainly during the spring and midsummer. Adult midges are most active during the evening and they may enter the mouth, eyes and ears, thus limiting evening activities outdoors and indoors. Evening breezes carried large adult swarms, estimated between 40-50 billion individuals/night (Van Poppelen internal report,1998), toward populated areas. Similar phenomena have been documented in various countries including Italy, Sudan and USA (reviewed by Ali 1996). Recently, Broza and Halpern (2001) showed that chironomid egg masses
might serve as the natural reservoir of the cholera bacterium, raising the chironomid problem from a nuisance level to a life-threatening hazard. This gives a new impetus to developing methods of monitoring and control of chironomid numbers. In this report we focus on the development of an efficient sampling technique suggesting and facilitating the establishment of an action threshold.