THE EFFECT OF TEMPERATURE ON THE TOXICITY OF TEMEPHOS TO BLACK FLY (DIPTERA: SIMULIIDAE) LARVAE

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Abstract
Different formulations of temephos were tested against Simulium venustum and S. vittatum larvae at water temperatures of 7 °to 20 °C under simulated stream conditions in the laboratory and the results indicated a significant positive correlation between water temperature and temephos efficacy. Temephos application of up to 5 mg/L/10 min had very little effect on Simulium larvae at 7 ° to 8 °C. Data from the tests indicated that both emulsifiable concentrate and wettable powder formulations have positive temperature coefficients. The WP formulation was 11 times and two EC formulations were 32 times more toxic at 20 °C than at 10 °C. The rate of larval detachment was faster at the higher temperatures but even at 20 °C detachment was not immediate as is common with larvae treated with methoxychlor. Detached larvae did not survive. On the basis of the present laboratory experiments on temperature–efficacy relationships, there are very strong indications that these formulations could be used effectively against black fly larvae only in streams that have water temperatures not less than 18 °to 20 °C.