Comparison of morning and evening larvicide applications on black fly (Diptera: Simuliidae) mortality

The downstream movement, or drift, of larval black flies as well as many other aquatic insects has been well documented. This phenomenon has most often been associated with the dusk-to-overnight time frame. Operationally, larvicide applications targeting black flies are typically initiated early in the day and can extend until near sunset. To determine if larvicide applications conducted late in the day would be affected by the drift behavior of larval black flies, 6 larvicide applications were conducted. Three applications were conducted at midmorning and 3 during the evening. Larvicidal applications of Bacillus thuringiensis subsp. israelensis insecticidal proteins targeting Simulium appalachiense demonstrated no difference in larval mortality between morning and evening applications. These findings indicate that the larvae responded in a similar manner to the larvicide during the late morning to early afternoon and evening to night. The drift behavior of larval black flies does not appear to be an impediment to black fly suppression activities.