The brown planthopper (Nilaparvata lugens Stål; BPH) is a specialist herbivore on rice (Oryza sativa) that ingests phloem sap from the plant through its stylet mouthparts. Electronic penetration graphs revealed that BPH insects spent more time wandering over plants carrying the resistance genes Bph14 and Bph15, but less time ingesting phloem than they did on susceptible plants. They also showed that their feeding was frequently interrupted. Tests with [ 14 C]sucrose showed that insects ingested much less phloem sap from the resistant than the susceptible plants. BPH feeding up-regulated callose synthase genes and induced callose deposition in the sieve tubes at the point where the stylet was inserted. The compact callose remained intact in the resistant plants, but genes encoding b-1,3-glucanases were activated, causing unplugging of the sieve tube occlusions in susceptible plants. Continuing ingestion led to a remarkable reduction in the susceptible plants' sucrose content and activation of the RAmy3D gene, leading to starch hydrolysis and ultimately carbohydrate deprivation in the plants. Our results demonstrate that BPH feeding induces the deposition of callose on sieve plates in rice and that this is an important defense mechanism that prevents insects from ingesting phloem sap. In response, however, the BPH can unplug sieve tube occlusions by activating b-1,3-glucanase genes in rice plants.

The fine structure of the salivary sheaths in plant tissues can provide important information on homopteran probing and ingestion behaviors. Salivary sheaths secreted by the brown planthopper (BPH), Nilaparvata lugens (Stål) (Homoptera: Delphacidae), and their tissue pathway were investigated using light, scanning electron, and transmission electron microscopy. About half of the salivary flanges on the surface of the food substrate were connected with internal salivary sheaths. Only 43% of the salivary sheaths showed side branches. Many sculpture-like protuberances and small cavities had been formed on the outer surface of the salivary sheath, but the sheath lumen circumferences were sealed. Brown planthoppers showed a preference for probing and leaving salivary sheaths in the susceptible rice variety TN1 rather than in the resistant variety B5 during the first 2 days of the experiments. The salivary sheaths in rice tissues reached the inner tissue layer of the leaf sheaths and stems, but were mostly observed to end in the first and second layer of the leaf sheaths. Brown planthoppers also preferred to probe into the thick segment of the outer leaf sheath. After ingestion by the insect, the cytoplasm in both phloem and companion cells degraded and the main organelles were lost. Numerous small vesicles were found in most of the phloem cells, but cell walls remained intact. Large numbers of symbiont-like structures were observed inside the salivary sheath lumen. These results indicated that BPH has complicated feeding behaviors, which warrants further investigation.

To determine the species of the yeast-like symbionts (YLS) in the brown planthoppers (BPH), Nilaparvata lugens, YLS were first isolated and purified by ultracentrifugation from the fat bodies of BPH, and then 18S rDNA and internal transcribed spacer (ITS)-5.8S rDNA sequences of YLS were amplified with the different general primers for fungi. The results showed that the two different 18S and ITS-5.8S rDNA sequences of YLS were obtained. One 2291-bp DNA sequence, which contained 18S and ITS-5.8S rDNA, showed the high similarity to Cryptococcus and was named Cryp-Like symbiotes. Another 1248-bp DNA sequence, which contained a part of 18S and ITS-5.8S rDNA, showed the high similarity to Pichia guilliermondii and was named Pichia-Like symbiotes. It was further proved that Cryp- and Pichia-Like symbiotes existed in BPH through nested PCR with specific primers for two symbiotes and in situ hybridization analysis using digoxigenin-labeled probes. Our results showed that BPH harbored more than one species of eukaryotic YLS, which suggested that diversity of fungal endosymbiotes may be occurred in planthoppers, just like bacterial endosymbiotes.

Brown planthopper (BPH) Nilaparvata lugens Stål is a serious insect pest of rice in Asian countries. Active compounds have close relationship with rice resistance against BPH. In this study, HPLC, MS/MS, and NMR techniques were used to identify active compounds in total flavonoids of rice. As a result, a BPH resistance-associated compound, Peak 1 in HPLC chromatogram of rice flavonoids, was isolated and identified as schaftoside. Feeding experiment with artificial diet indicated that schaftoside played its role in a dose dependent manner, under the concentration of 0.10 and 0.15 mg mL-1, schaftoside showed a significant inhibitory effect on BPH survival (p < 0.05), in comparison with the control. The fluorescent spectra showed that schaftoside has a strong ability to bind with NlCDK1, a CDK1 kinase of BPH. The apparent association constant KA for NlCDK1 binding with schaftoside is 6.436 × 103 L/mol. Docking model suggested that binding of schaftoside might affect the activation of NlCDK1 as a protein kinase, mainly through interacting with amino acid residues Glu12, Thr14 and Val17 in the ATP binding element GXGXXGXV (Gly11 to Val18). Western blot using anti-phospho-CDK1 (pThr14) antibody confirmed that schaftoside treatment suppressed the phosphorylation on Thr-14 site of NlCDK1, thus inhibited its activation as a kinase. Therefore, this study revealed the schaftoside-NlCDK1 interaction mode, and unraveled a novel mechanism of rice resistance against BPH.

The white-backed planthopper (WBPH) Sogatella furcifera is one of the most harmful pests of rice in Southeast Asia. The fat body of WBPH harbors intracellular yeast-like symbionts (YLS). YLS are vertically transmitted to WBPH offspring by transovarial infection. YLS play an important role in the WBPH life cycle. YLS diversity and function have been extensively studied in the brown planthopper (BPH) and small brown planthopper but not in WBPH, even though a novel strategy for controlling the BPH based on suppressing YLS has been proposed. Here, using denaturing gradient gel electrophoresis, we identified 12 unique fungal sequences among YLS of WBPH, and five of them represented uncultured fungi. We then fed WBPH with rice plants treated with different fungicides [70% propineb wettable powder (WP) (PR), 70% propamocarb hydrochloride aqueous solution (AS) (PH), 25% trifloxystrobin and 50% tebuconazole water-dispersible granules (WG) (TT), 40% pyrimethanil suspension concentrate (SC) (PY), and 50% iprodione SC (IP)] and evaluated their effects on YLS abundance and WBPH survival rate. Both YLS abundance and adult WBPH survival rate were significantly decreased upon feeding fungicide-treated rice plants, and exposure to 50% IP resulted in the strongest reduction. The abundance of two Sf-YLS species (Ascomycetes symbiotes and Cla-like symbiotes) was significantly reduced upon exposure to 50% IP. The counts of Ascomycetes symbiotes, the most abundant YLS species, were also suppressed by the other fungicides tested. In conclusion, 50% IP was the most effective fungicide, reducing YLS abundance and WBPH survival rate under controlled conditions, suggesting its potential use to control WBPH.