Botanical pesticides as potential rotifer-control agents in microalgal mass culture

With the aim of identifying an effective and safe technique for reducing rotifer contamination in microalgal mass cultivation, the toxic effects of four botanical pesticides on the rotifer Brachionus plicatilis were studied. Acute toxicity tests showed that celangulin, matrine and toosendanin are highly toxic to B. plicatilis, with 24 h LC50 values of 0.175 mg L− 1, 0.061 mg L− 1 and 2.132 × 10− 3 mg L− 1, respectively. Azadirachtin was the least toxic, with a 24 h LC50 value of 18.386 mg L− 1. Chronic toxicity tests showed that life history parameters (Ro, T, rm and λ) and population density of rotifers decreased significantly when exposed to 0.110 mg L− 1 celangulin, ≥ 0.050 mg L− 1 matrine or 0.380 × 10− 3 mg L− 1 toosendanin. In addition, the rotifer-control effects of toosendanin and its safety in Chlorella and Nannochloropsis sp. cultivation were evaluated. Results demonstrated that 1.755 − 2.132 × 10− 3 mg L− 1 toosendanin had no obvious toxic influence on final cell density and photosynthesis of Chlorella and Nannochloropsis sp., but effectively reduced the rotifer density and its fecundity. Based on the high toxicity to rotifers and the relative safety to microalgae, together with their low commercial price and ecological acceptability, celangulin, matrine and toosendanin are considered to be good potential botanical pesticides for controlling rotifers in microalgal mass culture.