Brown planthopper (BPH), a monophagous phloem feeder, consumes a large amount of photoassimilates in rice and causes wilting. A near-isogenic line ‘TNG71-Bph45’ was developed from the Oryza sativa japonica variety ‘Tainung 71 (TNG71) carrying a dominant BPH-resistance locus derived from Oryza nivara (IRGC 102165) near the centromere of chromosome 4. We compared the NIL (TNG71-Bph45) and the recurrent parent to explore how the Bph45 gene confers BPH resistance. We found that TNG71-Bph45 is less attractive to BPH at least partially because it produces less limonene. Chiral analysis revealed that the major form of limonene in both rice lines was the L-form. However, both L- and D-limonene attracted BPH when applied exogenously to TNG71-Bph45 rice. The transcript amounts of limonene synthase were significantly higher in TNG71 than in TNG71-Bph45 and were induced by BPH infestation only in the former. Introgression of the Bph45 gene into another japonica variety, Tainan 11, also resulted in a low limonene content. Moreover, several dominantly acting BPH resistance genes introduced into the BPH-sensitive IR24 line compromised its limonene-producing ability and concurrently decreased its attractiveness to BPH. These observations suggest that reducing limonene production may be a common resistance strategy against BPH in rice.

Rice planthoppers are common insect pests in Taiwan, and they have caused significant damage in the past. The majority of rice planthoppers have seen a drastic decline in their population since the mid-2000s, a trend that has anecdotally attributed to widespread and better pest control, as well as improved rice cultivation management. By analyzing 40 years of the airborne net trap data of rice planthoppers collected in Southwest Taiwan, it was found that the pests’ yearly population, computed with a logarithmic transformation, resembles a signature climate pattern in the global oceans with a robust multi-decadal variability. An ocean temperature-based index derived from the patterns of multi-decadal variability shows a marked resemblance with the population change of common rice planthoppers, with overlapping peaks during the 1990–2010 period. The climate dynamics associated with the regional weather pattern in the vicinity of Taiwan are discussed. Phase reversal of this multi-decadal climate variability in the future may produce favorable climatic conditions for the rice planthopper population to increase back to its historical levels.

The brown planthopper (BPH, Nilaparvata lugens) and white-backed planthopper (WBPH, Sogatella furcifera) are major rice pests, yet WBPH resistance and its overlap with BPH resistance remain poorly defined. Using the Rice Diversity Panel 1 (RDP1), screened against laboratory colonies, we mapped resistance to both pests across three panels and three models (MLM, FarmCPU, BLINK), examined leading loci with the High-Density Rice Array, and mined 3000-genome candidate-gene haplotypes. Resistance correlated weakly between pests (r = 0.26). We identified six BPH and five WBPH candidate loci, all ≥2.38 Mb from cloned Bph genes; correspondence with uncloned QTL cannot be excluded, and the WBPH chromosome 9 locus is the strongest novel candidate. Top signals did not co-locate and candidates shared most defense modules, but neither pattern exceeded chance in permutation testing, and the cross-trait genomic correlation was non-significant (r_g = 0.38, SE ≈ 0.33). These loci sit on a background of low genomic heritability; we can neither demonstrate pest-specificity nor exclude a shared polygenic background. Resistance-allele sources were subspecies-differentiated but locus-specific. This is the first parallel diversity-panel genome-wide association study of the two planthoppers and the first for WBPH host resistance. It provides positional candidates and candidate donor haplotypes as a validation-pending breeding resource.