No abstract

Species-specific changes in insecticide susceptibility were found in Asian rice planthoppers (i.e. BPH for imidacloprid and WBPH for fipronil). Insecticide resistance in BPH against imidacloprid occurred in East Asia and Indochina, but not in the Philippines. In contrast, insecticide resistance in WBPH against fipronil occurred widely in East and South-east Asia.

Ecological stoichiometry provides a novel context for elucidating the occurrence of intraguild predation. Recent data show that predators on average have a higher nitrogen content and lower C:N ratio than potential herbivorous prey. Thus, many predators may be nitrogen limited, and intraguild predation may allow them to increase their nitrogen intake and growth by supplementing a diet of herbivores with more nitrogen-rich intraguild prey. We tested this hypothesis using an assemblage of salt-marsh-inhabiting arthropods. First, we determined the nitrogen content and C:N ratio of taxa in four trophic groups (plants, herbivores, omnivores, and predators). Second, we fed an intraguild predator, the wolf spider Pardosa, one of three diets (herbivores, intraguild prey, or an alternating mix of the two) and measured spider survival, growth, capture rate, and biomass and nitrogen intake.In general, body nitrogen content increased and C:N ratio decreased from lower to higher trophic levels for marsh-inhabiting species, with predators having a higher nitrogen content and lower C:N ratio than herbivores. Performance experiments showed that in one case Pardosa ingested more biomass and nitrogen and grew faster on a diet of intraguild prey (the planthopper egg predator Tytthus) than on a diet of herbivores (the planthopper Prokelisia dolus). This occurred because Pardosa captured more Tytthus than Prokelisia and not because Tytthus (a stoichiometric exception) was higher in nitrogen content. In another case, Pardosa grew slower on a diet of intraguild prey (the web-building spider Grammonota) than on a planthopper diet even though Grammonota was more nitrogen rich, a result we attribute to prey behavior and risk of predation. Mass gain and nitrogen intake in Pardosa were highly correlated with the biomass of prey consumed. However, after accounting for the biomass of prey consumed across all diet treatments, we found little evidence that either the nitrogen content or C:N stoichiometry of prey contributed to Pardosa's growth. Thus, there was little support for the hypothesis that the nitrogen stoichiometry of prey directly confers a performance advantage to Pardosa and in itself promotes intraguild predation. In this system, characteristics other than the nitrogen stoichiometry of prey play a significant role in prey capture and predator performance. Nonetheless, by supplementing their diet with readily captured intraguild prey, predators such as Pardosa can increase their nitrogen intake and performance.

Species-specific insecticide resistance (imidacloprid resistance in N. lugens and fipronil resistance in S. furcifera) is ongoing in populations of the two planthoppers immigrating into Japan.

The virulence of laboratory strains of the brown planthopper (BPH), Nilaparvata lugens (Stål), and the whitebacked planthopper (WBPH), Sogatella furcifera (Horváth), collected in Japan between 1966 and 2005, was evaluated using rice differential varieties carrying different planthopper resistance genes. The BPH strain collected in 1966 was avirulent to all the rice varieties tested. In contrast, the 1989, 1999 and 2005 strains were virulent to Mudgo, which carries Bph1. The 1999 and 2005 strains were virulent to ASD7 (bph2). Thus, the virulence status of the laboratory BPH strains was the same as in previous reports. The 1989The , 1999The , and 2005 WBPH strains were virulent to N22 (Wbph1), Mudgo, ASD7, Babawee (bph4) and Chin Saba (bph8); the 1999 and 2005 WBPH strains were also virulent to ARC10239 (Wbph2). Although the virulence status of WBPH in Japan has not previously been studied, the present results suggest that the effectiveness of the Wbph1 resistance gene broke down before 1989, while that of Wbph2 broke down between 1989 and 1999. The present study showed that long-term mass rearing in the laboratory has not affected virulence status. Thus, these strains will be useful to analyze resistance genes against BPH and WBPH.

SUMMARYA pre-infestation of the white-backed planthopper (WBPH), Sogatella furcifera Horvá th, conferred resistance to bacterial blight caused by Xanthomonas oryzae pv. oryzae (Xoo) in rice (Oryza sativa L.) under both laboratory and field conditions. The infestation of another planthopper species, the brown planthopper (BPH) Nilaparvata lugens Stå l, did not significantly reduce the incidence of bacterial blight symptoms. A large-scale screening using a rice DNA microarray and quantitative RT-PCR revealed that WBPH infestation caused the upregulation of more defence-related genes than did BPH infestation. Hydroperoxide lyase 2 (OsHPL2), an enzyme for producing C 6 volatiles, was upregulated by WBPH infestation, but not by BPH infestation. One C 6 volatile, (E)-2-hexenal, accumulated in rice after WBPH infestation, but not after BPH infestation. A direct application of (E)-2-hexenal to a liquid culture of Xoo inhibited the growth of the bacterium. Furthermore, a vapour treatment of rice plants with (E)-2-hexenal induced resistance to bacterial blight. OsHPL2-overexpressing transgenic rice plants exhibited increased resistance to bacterial blight. Based on these data, we conclude that OsHPL2 and its derived (E)-2-hexenal play some role in WBPH-induced resistance in rice.

The brown planthopper (BPH), Nilaparvata lugens (Stål), is one of the most serious and destructive pests of rice, and can be found throughout the rice-growing areas of Asia. To date, more than 24 major BPH-resistance genes have been reported in several Oryza sativa ssp. indica cultivars and wild relatives. Here, we report the genetic basis of the high level of BPH resistance derived from an Indian rice cultivar, ADR52, which was previously identified as resistant to the whitebacked planthopper (Sogatella furcifera [Horváth]). An F2 population derived from a cross between ADR52 and a susceptible cultivar, Taichung 65 (T65), was used for quantitative trait locus (QTL) analysis. Antibiosis testing showed that multiple loci controlled the high level of BPH resistance in this F2 population. Further linkage analysis using backcross populations resulted in the identification of BPH-resistance (antibiosis) gene loci from ADR52. BPH25 co-segregated with marker S00310 on the distal end of the short arm of chromosome 6, and BPH26 co-segregated with marker RM5479 on the long arm of chromosome 12. To characterize the virulence of the most recently migrated BPH strain in Japan, preliminary near-isogenic lines (pre-NILs) and a preliminary pyramided line (pre-PYL) carrying BPH25 and BPH26 were evaluated. Although both pre-NILs were susceptible to the virulent BPH strain, the pre-PYL exhibited a high level of resistance. The pyramiding of resistance genes is therefore likely to be effective for increasing the durability of resistance against the new virulent BPH strain in Japan.

A novel viral disease of rice caused by Southern rice black-streaked dwarf virus (SRBSDV) has spread throughout East and Southeast Asia since the mid-2000s. Outbreaks of this viral disease occur yearly in southern parts of Japan concurrently with overseas migration of the planthopper vector Sogatella furcifera from southern China during the rainy season (from late June to early July). We examined the dynamics (changes in titer and localization) of SRBSDV on rice using reverse-transcription real-time polymerase chain reaction and determined the relationship between virus titer in plants and virus acquisition by S. furcifera. Under a constant temperature of 27°C, a substantial increase of SRBSDV titer in the leaf sheath together with typical symptoms (stunted growth and twisting of leaf tips) was observed at 20 days after the end of a 7-day exposure of viruliferous S. furcifera. Approximately 40% of S. furcifera acquired SRBSDV through feeding for 5 days on rice plants that were infected following exposure to viruliferous vectors for 10 to 15 days. These results suggest that rice infected by S. furcifera can be a source of SRBSDV before the next generation of S. furcifera emerges.