Treatment potential of a synergistic botanical pesticide combination for rotifer extermination during outdoor mass cultivation of Spirulina platensis

Rotifer-control effects of a synergistic celangulin/toosendanin (CA/TSN) combination at a 1:9 ratio, and its safety for Spirulina platensis growth, were studied. Two additions of 0.003-0.006 mg/L of the combination inhibited rotifer reproduction within 3 days, and showed no toxicity toward algal biomass and phycocyanin levels. A comparison between the CA/TSN and NH4HCO3 treatments indicated that 200 mg/L NH4HCO3 produced more acute toxicity based on ammonia intoxication, while 0.003 mg/L CA/TSN showed lasting effects by sterilizing rotifers. In the NH4HCO3 treatment, rotifers still had slow reproduction, partially owing to ammonia volatilization. Neither the NH4HCO3 nor CA/TSN treatment changed algal filament morphology; however, the NH4HCO3 treatment initially inhibited algal growth more significantly. S. platensis treated by the CA/TSN combination reached higher biomass in the same time frame. Given its effectiveness, together with projected farm-earnings increase, the CA/TSN combination showed excellent potential and economic feasibility for rotifer extermination in outdoor mass cultures of S. platensis.