Objective To observe the larvicidal action of transgenic cyanobacterium with the CryIVD gene of Bacillus thuringiensis sub.israelensis.Methods Transgenic cyanobacterium was cultured in large quantities and counted under a light microscope.Its larvicidal action was evaluated in the field in the City of Jining,Shandong Province.Results The transgenic cyanobacterium was highly toxic to the larvae of Culex pipiens.When the concentration of the engineered cyanobacterium was 106 cells/ml,it killed more than 99% o...