A change in biotype property of brown planthopper populations immigrating into Japan and their probable source areas

Abstract

A gradual but significant change in biotype property of the yearly immigrants of the brown planthopper (BPH) was observed during the period from 1987 to 1991 in Japan. Saikai-184, a breeding line of rice with the Bphl gene, was resistant to BPH immigrants in 1987, but became susceptible in 1990. Honeydew measurements with BCG-filter paper and parafilm sachet revealed that the BPH females immigrating in 1990 and 1991 excreted as much honeydew on Saikai-184 as on the susceptible variety Reihou. Also, the 1987 immigrants excreted little honeydew on IR26 with the Bphl gene, but the 1990-immigrants excreted considerable amounts of honeydew on it. The percentage of individual females which excreted more than 10 mg of honeydew per day was only 10% in the 1987-immigrants, whereas it was increased up to 30-40% in the 1990-immigrants. Both the 1987- and 1990-immigrants had little ability to feed on IR42 with the bph2 gene. These findings indicate that the BPH immigrants into Japan are changing from biotype 1 to biotype 2. Similar biotype shifts have been reported correspondingly in south China and north Vietnam. This may indicate that south China and north Vietnam are the possible source areas for the overseas immigrants of BPH into Japan.