Abstract: Objective  To study biological safety of the molluscicidal ingredient（MI， a kind of diketopiperazines） in the exocellular broth of Aspergillus fumigatus SL-30’ which was isolated from the rhizosphere of Phytolacca acinosa.   Methods  The MI was prepared in concentrations ranging from 0.01 to 0.60 mg/L, at the same time molluscicidal activity against Oncomelannia hupensis was tested by using immersion method, and the LC₅₀ in the case of immersion time for 24, 48 and 72 h was calculated. Acute toxicity of the MI with concentration ranging from 0.5 to 4.0 mg/L on Brachydanio rerio, Macrobrachium nippoensis and Rana limnochris was performed by standard laboratory procedure, and mortality rate of the tested animals with treated time of 24, 48 and 72 h was recorded. Effect of the MI on Eisenia fetida was tested using natural soil procedure with the dose of 1 and 10 mg/kg, and the poisoning performance and mortality in the 7th day and 14th day were recorded. Inhibition of the MI at 10 mg/kg on respiration of soil microorganisms was determined by sealed alkaline direct absorption method, and the released amount of CO₂（mg/100 g） in the 2nd, 5th, 7th, 10th, 12th and 15th day was determined.  Results  Molluscicidal activity of the MI against Oncomelania hupensis was shown with LC₅₀ 0.101，0.062, and 0.022 mg/L in 24, 48 and 72 h, respectively. Mortality rate of Brachydanio rerio, Macrobrachium nippoensis and Rana limnochris all increased with the increase of MI concentration, and the LC₅₀ of each kind of tested animals was recorded as follows: 1.941, 1.755 and 1.219 mg/L for Brachydanio rerio, 3.170, 2.720 and 2.419 mg/L for Macrobrachium nippoensis, 2.109, 1.751  and 1.288 mg/L for Rana limnochris in 24 , 48 and 72 h, respectively. The LC₅₀ of MI on Eisenia fetida was >10.0 mg/kg. The inhibition rate of MI was less than 50% with a concentration of 10 mg/kg in 15 days.  Conclusion  The MI shows molluscicidal activity on Oncomelania hupensis with much lower toxicity on Brachydanio rerio,  Macrobrachium nippoensis and Rana limnochrisn. The MI is safe to non-target aquatic organisms, and to both Eisenia fetida and soil microorganisms under the effective mollussicidal concentration.

Key words: Diketopiperazines, Oncomelania hupensis, Non-target organisms