Effects of asplanchnin allelochemical on the toxicity of triasulphuron herbicide to rotifer Brachionus patulus (Rotifera: Brachionidae)

We evaluated the effects of 4 concentrations (15, 30, 60 and 120 mu g L-1) of triasulphuron on the population growth of rotifer Brachionus patulus. The rotifers were cultured at an algal density of 0.25 x 10(6) cells mL(-1) of Chlorella vulgaris for 15 days and with and without the presence of asplanchnin allelochemical obtained from the predator Asplanchna sieboldi. Regardless of the presence of asplanchnin, the population density of B. patulus decreased with increasing concentration of triasulphuron and its populations drastically reduced when grown with triasulphuron herbicide at 120 mu g mL(-1). At any given triasulphuron concentration, B. patulus + asplanchnin showed significantly higher peak abundances and higher growth rates than populations cultured without asplanchnin. The population growth rates varied from +0.23 to -0.13 per day, depending on the presence or absence of asplanchnin and the concentration of the herbicide. Our results suggest that infochemicals from Asplanchna may influence the population abundances of the prey brachionids in ponds and takes that receive effluents containing herbicides.