Abstract: To develop a new microbial pesticide,a symbiotic fungi named as NJ-1 was isolated from the stem of Arctium lappa L.and the extracts from the mycelium and the fermentation broth were studied in terms of insecticidal activity.The fungus was isolated from stems of health A.lappa, and the crude extracts were obtained by purification and fermentation.Brine shrimp was used as a biological model to screen substance with the insecticidal activity. NJ-1 was identified to be Neurospora tetrasperma. The median lethal dose LD₅₀ of the extracts from the mycelium and the fermentation broth were 0.84 mg/mL and 0.27 mg/mL, respectively. The activity of the extract from NJ-1 fermentation broth was 1.3 times greater than DDVP when compared with three kinds of chemical pesticides (cypermethrin,DDVP and omethoate). NJ-1 had significant insecticidal activity to brine shrimp, which may provide a new biological resource to explore new microbial insecticide.

Key words: Arctium lappa L.;symbiotic fungi, Neurospora tetrasperma, brine shrimp;LD₅₀