Control of Chironomid Midges in Recreational Lakes13

Abstract

Several commonly available and experimental insecticides were evaluated for control of chironomid midge larvae, Chironomus spp., Proclaideus spp., and Tanytarsus spp. in 2 recreational lakes. In Lake Calabasas, where the bottom has a thin layer of mud on a surface of cement, standard midge larvicides such as Abate® ( O, O -dimethyl phosphorothioate O, O -diester with 4,4′-thiodiphenol) and fenthion proved highly effective. Fenthion at 0.5 Ib per surface acre controlled the larvae for more than 7 weeks. At this rate of application very slight mortality of the mosquito fish Gambusia affinis (Baird & Girard) was observed. Abate at 0.75 pounds per acre controlled the midges for about 4–5 weeks and caused slight mortality of the fish. Dursban® ( O, O -diethyl O -(3,5,6-trichloro-2-pyridyl) phosphorothioate) at the rate of 0.2 Ib/acre yielded long-lasting control of midge larvae, the suppression lasting for almost 5 months. In Westlake (about 10 miles from Lake Calabasas), with a natural bottom, where small portions were treated, fenthion at 0.5 lb/acre yielded little or no control of the midge larvae. Abate at 0.5 pounds per acre produced similar results. Carbaryl at 0.5 and 1.0 pounds per acre yielded good control, but its longevity was for only 2-3 weeks. Dursban insecticide applied as granules or sprays at 0.2 pounds per acre yielded excellent control of midge larvae. The granular formulations produced better and longer-lasting larval control than an emulsifiable concentrate formulation. The latter formulation at 0.2 lb/acre or higher rate caused slight kill of blugill, Lepomis macrochirus Rafinesque; largemouth bass, Micropterus salmoides Lacepede; and black crappie, Pornoxis nigromaculatus (Le Sueur) in the lake. No mortality of fish was observed in plots treated with a granular formulation of Dursban at the same rate.