Aquatic bioassay of 11 pesticides using larvae of the mosquito, Wyeomyia smithii (Diptera: Culicidae).

One of the uses of aquatic bioassays is to determine the presence or absence of toxic contaminants in water from the field. Our Laboratory has developed a bioassay system for this purpose using larvae of the pitcher-plant mosquito, W eom ia smithii (Coquillett) (Strickman 1984). V The major app lcation of this system is the investigation of minor fish kills which may occur at any U.S. Air Force base. The system was developed around a number of requirements, including: (1) Simplicity so that it may be taught to technicians who rotate from their jobs frequently; (2) Economy of space and time; (3) Tolerance to uncontaminated water from a wide variety of sources; (4) Capability of testing small samples of water in order to reduce shipping costs; and (5) Capability of detecting toxicants at levels at or below the LC50 for common species of fish. The Wyeomyia bioassay proved to be a practical tool in the investigation of over 20 fish kills during 1983 and 1984. Toxicants detected by the bioassay were later identified as engine lubricating oil, copper, paint stripper, and high levels of free ammonia. Water from the sites of many of the fish kills produced no effect on larvae, indicating that the fish kills had not involved toxic contaminants or that contaminants had dissipated by the time of sampling or bioassay. Such negative results were important because they indicated that chemical analysis would probably not have been productive. Elimination of unnecessary analyses saved over $15,000 during a single year.