Development of virulence to resistant rice varieties in the brown planthopper, Nilaparvata lugens (Homoptera: Delphacidae), immigrating into Japan

Abstract

Virulence of the brown planthopper Nilaparvata lugens strains, which immigrated into Japan between 1997 and 1999, was examined on five rice varieties, Mudgo (carrying a resistance gene Bph 1), IR26 (Bph 1), ASD7 (bph 2), Norin PL10 (Bph 3), and Babawee (bph 4). Newly emerging brachypterous females of N. lugens were released on test rice plants at the tillering stage, and we defined the females that became heavily swollen or survived for five days as virulent. Between 45 and 87% of the females were virulent to ASD7, although such high virulence had not been detected before 1997. Between 49 and 98% of the females were virulent to Mudgo and IR26. Virulence to rice varieties carrying Bph 1 in the N. lugens population has continued to become stronger since the 1988-1990 period in which changes in virulence were first found. In contrast, virulence of the N. lugens strains to Norin PL10 and Babawee was still at a low level, with 5 to 27% of the females being virulent. The results indicate that the resistance of Bph 1 has probably broken down and the resistance of bph 2 may be becoming ineffective for the N. lugens populations immigrating into Japan.