The Effects of Three Herbicides on Larvae of the Phantom Midge, 'Chaoborus punctipennis' (SAY).

摘要

The third and fourth instar larvae of Chaoborus punctipennis,planktonic dipterans important both as predators and prey in lakes and reservoirs,were subjected to static tests of various concentrations of three commercial herbicides: Chipmans 2,4-D Amine No. 4;Ortho Brush Killer A,and Amino Triazole Weedkiller. Larvae and dilution water were collected from Lake Loudoun Reservoir,Knox County,Tennessee. Observations of larval response (immobilization) were conducted every six hours for the first 48hours of each test and every 12hours for at least the next 48hours. A toxicity curve was constructed for each test by plotting time to 50percent response against concentration. The 96hour (100hour) IC50values for 2,4-D and ammonium sulfamate herbicides at 15C were 890ppm and 3430ppm,respectively--concentrations far higher than likely to be encountered in the natural environment. The toxicity of ammonium sulfamate appeared to interact significantly with temperature,however,as IC50values at 20C generally ran about half those at 15C. Although computer analysis of data from amitrole tests produced no significant regressions of response on concentration,this herbicide is considered potentially the most hazardous of the three herbicides to Chaoborus populations.