LABORATORY EVALUATION OF THE INSECT GROWTH REGULATOR DIFLUBENZURON AGAINST BLACK FLY (DIPTERA: SIMULIIDAE) LARVAE AND ITS EFFECTS ON NONTARGET STREAM INVERTEBRATES

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Abstract
In laboratory tests conducted under simulated stream conditions treatment with the insect growth regulator diflubenzuron at 1.0 mg/L/30 min at 15°C resulted in 100% mortality of Simulium larvae after 10 days. At 0.5 mg/L/15 min there was 97.6% mortality of S. vittatum larvae after 18 days in water at 10.5°C. Diflubenzuron was less effective when the growth rate of simuliid larvae during the test was slow due to inadequate nutrition, and it was more effective at 25 than at 20°C, but there was no difference in efficacy between 10 and 20°C. Efficacy against simuliid larvae varied inversely with their instar. Diflubenzuron at 1.0 mg/L/30 min was tested in the laboratory against selected nontarget invertebrates. Among the Ephemeroptera tested at 15°C, Baetis pygmaeus, Leptophlebia sp., and Isonychia sp. proved susceptible but not Stenonema fuscum and Ephemerella subvaria. Similarly diflubenzuron had little effect on the perlid stonefly Paragnetina media at 15°C and on the filter-feeding caddisfly Hydropsyche betteni at 20°C. Chironomid larvae (Phaenopsectra sp.) tested at 20°C were affected and the amphipods Gammarus pseudolimnaeus and Hyalella azteca were particularly susceptible at 25 but not at 15°C.