Brown planthopper (BPH) (Nilaparvata lugens Stål) is a significant insect pest of rice (Oryza sativa L.). We constructed a gene‐pyramided japonica line, in which two BPH resistance genes Bph1 and Bph2 on the long arm of chromosome 12 independently derived from two indica resistance lines were combined through the recombinant selection. The gene‐pyramiding was achieved based on the previously constructed high‐resolution linkage maps of the two genes. Two co‐dominant and four dominant PCR‐based markers flanking the loci were used to select for a homozygous recombinant line in a segregating population that was derived from a cross between the parental homozygous single‐gene introgression lines. BPH bioassay showed that the resistance level of the pyramided line was equivalent to that of the Bph1‐single introgression line, which showed a higher level of resistance than the Bph2‐single introgression line. The pyramid line should provide a useful experimental means for studying the fine structure of the chromosomal region covering these two major BPH resistance genes.

The brown planthopper, Nilaparvata lugens, is a serious pest of rice crops throughout Asia and exhibits wing dimorphism, with brachypterous adults having reduced wings and macropterous adults possessing fully developed wings. To understand the reproductive strategies in two wing-morphs of this insect, the transcript encoding the major yolk protein precursor, vitellogenin (Vg), was cloned. The complete mRNA transcript was 6314 bp, which encodes a protein of 2063 residues including an 18-residue putative signal peptide. Analysis of the mature protein revealed two vitellogenin-N (or lipoprotein amino-terminal) domains near the N-terminus and a von Willebrand factor type D domain near the C-terminus. In addition, a highly conserved motif GL/ICG, and a number of cysteine residues were identified near the C-terminus. Northern blot analysis identified a ∼6.8 kb Vg gene transcript that was expressed exclusively in the adult female fat body cells. The expression profile revealed that the Vg gene starts to be expressed earlier (on day 3) in brachypters as compared to macropters where the mRNA transcript was observed on day 4. However, in both morphs, the amount of Vg mRNA increased to reach high levels during vitellogenic periods [from day 4 (in brachypters) and day 5 (in macropters) and onwards]. Reflecting the RNA transcription pattern, the Vg signal was detected by immunoblotting on day 3 and day 4 in haemolymph of brachypterous and macropterous females, respectively, and that was increased every day and remained high during the vitellogenic periods. Furthermore, the topical application of juvenile hormone (JH) III had up-regulated the Vg gene expression suggesting that the Vg gene is regulated by JH in N. lugens. In addition, it was demonstrated by Southern blot analysis that there exists a single copy of the gene in the N. lugens genome. A delayed trend in expression (of both the transcript and the protein) demonstrated by macropterous females in the present studies supports the hypothesis of prereproductive long distance migration in this wing-dimorphic species.

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