Black fly larvae (Diptera:Simuliidae) offer many unique opportunities for use in water quality studies. However, they are underutilized due to their perceived ecological importance and sensitivity to aquatic pollutants in comparison to the invertebrate groups routinely used in biomonitoring and aquatic toxicity tests. In our current study, we are looking at the impacts of lawn care practices on aquatic ecosystems, especially impacts of insecticides entering suburban watersheds on macroinvertebrate populations. Three of the most common insecticides detected in the Flint River watershed near Peachtree City, Georgia, carbaryl, chlorpyrifos, and malathion, have been evaluated in the lab to determine their respective 48 hr LC50 value to Simuliium vittatum IS-7 larvae using an orbital shaker bioassay. Results of the 48 hr LC50 tests reported as the median with fiducial limits, have shown chlorpyrifos to be the most toxic to black fly larvae [LC50=0.43 mg/L (0.39-0.48)] followed by carbaryl [LC50=28.95mg/L (27.29-30.58)], and malathion [LC50=84.76 mg/L (68.94-105.94)]. These insecticides were also tested as binary and ternary mixtures using the toxic unit (TU) approach. Toxicity was shown to be greater than additive for the ternary mixture of chlorpyrifos/carbaryl/malathion [LC50=0.57TU (0.47-0.66)], and the binary mixtures of chlorpyrifos/malathion [LC50=0.72 TU (0.60-0.83)], and carbaryl/malathion [LC50=0.78 TU (0.70-0.85)]. The binary combination of chlorpyrifos and carbaryl was shown to be additive [LC50=0.98 TU (0.90 -1.05)]. These results indicate that increased toxicity may be elicited in streams where all three chemicals are present.
Species 1: Diptera Simuliidae Simulium vittatum IS-7 (black flies)
Keywords: Insecticides, Toxicity Evaluations
The ESA 2001 Annual Meeting - 2001: An Entomological Odyssey of ESA