AbstractThreeBacillus thuringiensisflagellar (H) serogroups were newly detected in the populations associated with sericultural and natural environments of Japan. A total of 44B. thuringiensisstrains, derived from seven prefectures in Honshu, Shikoku, and Kyushu, were assigned to the H serotypes 34 (serovarkonkukian), 35 (serovarseoulensis), and 43 (serovarguiyangiensis). Of the 44 strains, three of the serovarkonkukianand one strain of the serovar guiyangiensis exhibited moderate larvicidal activity specific for the mosquito,Aedes aegypti. None of the strains showed toxicity against larvae of the silkworm,Bombyx mori.