Insect Growth Regulators for Control of Chironomid Midges in Residential-Recreational Lakes1

Abstract

Application of 2 insect growth regulators (IGRs) to 2 residential-recreational lakes produced excellent control of most aquatic nuisance midges. Methoprene at the rate of 0.25 lb/acre-surface to a shallow lake (Lake Calabasas, 6 ft deep) yielded excellent inhibition of emergence 3–4 days after treatment, and the duration of desired inhibition of emergence (IE) ranged from 1–3 wk, the duration of (IE) becoming shorter on successive treatments. Larval populations were not markedly suppressed by methoprene treatments. Dimilin® [1-(4-chlorophenyl)-3(2,6-difluorobenzoyl)-urea] at 0.1 and 0.25 lb/acre-surface produced excellent IE of midges in Lake Calabasas; however, after elimination of the prevailing midge fauna, the midge Labrundinia maculata (Roback) absent from Lake Calabasas heretofore appeared in the lake. Two additional treatments with Dimilin, including one at 0.25 lb/acre-surface did not effectively control L. maculata . All Dimilin treatments reduced larval populations except that of the new invader. Spring Valley Lake, covering 200 acres area and 12 ft deep, was treated with 0.1 and 0.21 lb/acre-surface of Dimilin. Due to the greater depth of this lake and the resultant low concentration of the IGR, high level of inhibition of emergence was obtained for only 4 wk or so with lower rate and 6–8 wk with the higher rate.