Demographic Parameters of Long-term Laboratory Strains of the Brown Planthopper, Nilaparvata lugens Stål, (Homoptera: Delphacidae) on Resistance Genes, bph20(t) and Bph21(t) in Rice

The demographic parameters of four laboratory strains of the brown planthopper (BPH), Nilaparvata lugens (Stål) collected in Japan between 1966 and 2005, were evaluated using near-isogenic lines (NILs) and pyramided line (PYL) of rice carrying recently identified genes, bph20(t) and Bph21(t) conferring resistance to BPH. Six traits: adult survivorship, development of female abdomen, nymph survivorship, nymphal developmental period, adult body weight, and oviposition were examined. Based on the adult survivorship and development of female abdomen, the BPH strains of Hatano-66 and Chikugo-89 were avirulent to bph20(t)-NIL and Bph21(t)-NIL as well as their PYL carrying both bph20(t) and Bph21(t). On the other hand, the BPH strains of Isahaya-99 and Nishigoshi-05 were virulent to bph20(t)-NIL and Bph21(t)-NIL but still avirulent to their PYL. Four other demographic parameters of the avirulent strains of BPH showed low nymph survivorship, prolonged nymphal developmental period, light body weight of adults and small number of eggs laid on the resistant lines to BPH. These results suggest that a resistance mechanism such as feeding inhibition caused by the two major genes resistance to BPH, similarly affect both on nymphal and adult stages. The PYL with both bph20(t) and Bph21(t) had an epistatic effect of resistance to the BPH strains migrated into Japan since 1999.