Field Evaluation of Simulium Larvicides: Effects on Target and Nontarget Insects

Abstract

The effectiveness of three blackfly larvicides, FMC-45497 (10% EC) [(-)-cyano )-3-3 phenoxybenzyl-(±) cis -3-(2,2-dichlorovinyl)-2,2-dimethyl cyclopropane-1-carboxylate], Abate® (50% EC) [ 0,0,0',0' -tetramethyl-0-0'-thiodi- p -phenylene phosphorothioate], and the insect growth regulator (IGR) Dimilin® (25% WP) [1-(4-chlorophenyl)-3-(2,6-difluorobenzyl) urea], was studied in the field against target Simulium , and their impact on selected aquatic nontarget insects was determined. Effectiveness and impact were assessed by three sampling techniques: drift net, Surber sampler, and polyethylene strips. Interval drift samples gave rapid evaluation of the effectiveness of the fast-acting larvicides FMC-45497 and Abate®. For Dimilin®, which is slow-acting, Surber sampler and polyethylene strips were more suitable because drift among aquatic organisms was not induced when Dimilin® was applied at 0.1 ppm/15 min. After the application of FMC-45497 at the rate of 0.01 ppm/15 min, catastrophic drift was noted in some components of the aquatic fauna, Baetis , Chironomidae, Hydropsyche , and Odonata. Baetis naiads constituted over 85% of the drifting organisms in number. Abate® applied at 0.1 ppm/15 min was selective, producing drift in Simulium larvae only, and Dimilin® at 0.1 ppm/15 min caused moderate decline in Simulium larvae and Baetis and Hydropsyche .