BIOTYPE COMPARISONS OF THE BROWN PLANTHOPPER, NILAPARVATA-LUGENS (HOMOPTERA, DELPHACIDAE) COLLECTED IN JAPAN AND THE INDO-CHINA PENINSULA

We compared biotypes of the brown planthopper (BPH) populations collected in Japan and Indochina Peninsula in 1992 to investigate possible source areas of the planthoppers that invade Japan. We quantified the honeydew excreted by the insects on six standard rice varieties to determine their biotypes. Eight populations used were roughly classified into two groups according to virulence to ASD7 rice with a bph2 resistant gene. Low proportions (10-30%) of planthoppers in Japanese and Red River Delta populations were capable of feeding on ASD7, unlike most planthoppers (80-93%) from the tropical Indochina Peninsula. On IR26, which has a Bph1 resistant gene, Japanese and Red River Delta planthoppers excreted ca. 30-50% of the quantity of honeydew excreted by BPH feeding on TN1 (no resistant gene), indicating the moderate susceptibility of the former to these planthoppers. Tropical populations collected from Mekong Delta and Thailand had slightly higher virulence to IR26. Rath Heenati and Babawee with Bph3 and bph4 resistant genes, respectively, remained highly resistant to all populations except those of the Mekong Delta. As a result, the biotype of Japanese populations bore a close resemblance to that of Red River Delta populations.