Susceptibility of black fly larvae (Diptera: Simuliidae) to lawn-care insecticides individually and as mixtures

• Published in: Environmental toxicology and chemistry 2003-07, Vol.22 (7), p.1582-1588
• Main Authors: Overmyer, Jay P., Armbrust, Kevin L., Noblet, Ray
• Format: Article
• Language: English
• Subjects: Animal, plant and microbial ecology; Animals; Applied ecology; Biological and medical sciences; Carbaryl - toxicity; Chlorpyrifos - toxicity; Drug Interactions; Ecotoxicology, biological effects of pollution; Effects of pollution and side effects of pesticides on protozoa and invertebrates; Environmental pollutants toxicology; Fresh water environment; Fundamental and applied biological sciences. Psychology; General aspects; Insecticide mixtures; Insecticides; Insecticides - toxicity; Larva; Lethal Dose 50; Malathion - toxicity; Medical sciences; Simuliidae; Simulium vittatum; Suburban watersheds; Toxicity; Toxicology; Water Pollutants, Chemical - toxicity
• ISSN: 0730-7268; 1552-8618
• DOI: 10.1002/etc.5620220722

Urban and suburban watersheds have the potential to be highly impacted by chemicals, especially insecticides to control insect pests on lawns, ornamental plants, and home gardens. Three of the most common lawn‐care insecticides detected in urban watersheds, carbaryl, chlorpyrifos, and malathion, have been evaluated using an acute orbital shaker toxicity test to determine their respective concentrations that produce 50% mortality (LC50) in Simulium vittatum Zetterstedt cytospecies IS‐7 larvae. Results of the 48‐h LC50 tests show chlorpyrifos to be the most toxic to black fly larvae (LC50 = 0.28 μg/L) followed by carbaryl (LC50 = 23.72 μg/L) and malathion (LC50 = 54.20 μg/L). 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 = 0.56 TU) and the binary mixtures of chlorpyrifos—malathion (LC50 = 0.72 TU) and carbaryl‐malathion (LC50 = 0.78 TU). The binary combination of chlorpyrifos and carbaryl was shown to be additive (LC50 = 0.98 TU). These results indicate that aquatic invertebrate populations in urban and suburban streams may experience a higher‐than‐expected increase in toxicity‐related effects when all three chemicals are present in the waterway.