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This study examines the utility of resistant varieties and their associated resistance genes against brown planthopper, Nilaparvata lugens (Stål), populations from South and South East Asia. A collection of 39 rice accessions that included resistant, tolerant and susceptible varieties and breeding lines were examined for performance against populations of N. lugens from India (4), Bangladesh (1), Myanmar (1), Vietnam (1), Indonesia (1), China (1), Taiwan (1), and the Philippines (2). Planthopper virulence varied between regions; however only 6 varieties were generally less damaged than the susceptible check Taichung Native 1 (TN1) among ≥50% of the test populations. Each of these 6 varieties contained multiple resistance genes. One further variety, also with multiple resistance genes, and a modern cultivar (possibly with the Bph3 gene) were moderately effective against the South Asian populations, whereas a traditional variety with the Bph6 gene was effective against South East Asian populations. Bph1, bph2, bph5, bph7, bph8, Bph9, Bph10 and Bph18 were ineffective against most planthopper populations. Bph20, Bph21, and Bph17 have potential to be used in resistance breeding in both South and South East Asia, whereas BPH25 and BPH26 have potential for use in South Asia. The results indicate that only a few of the currently available resistance genes will be effective in monogenic rice lines; but that pyramiding of two or more genes with strong to weak resistance could improve resistance strength and durability as apparent with the most resistant, traditional varieties. Strategies to avoid planthopper adaptation to resistant rice varieties are discussed.

We investigated the mechanism of brown planthopper, Nilaparvata lugens (Stål), resistance in the popular rice cultivar IR64, and the current level of resistance of IR64 to N. lugens in a large rice growing area with low brown planthopper populations (Central Luzon, Philippines). In greenhouse experiments with N. lugens populations collected from Central Luzon, IR64 showed slight to moderate levels of antibiosis, antixenosis, and tolerance relative to the cultivars IR22 and Azucena, which contain no major genes for N. lugens resistance. IR64 was also more resistant than IR26 in most experiments, despite the fact that both varieties have the same major gene for N. lugens resistance, Bph1. This confirms that IR64 contains one or more additional, apparently minor, genes for brown planthopper resistance. Our findings also demonstrate that, in an area with low insecticide use, it is not necessary to have high levels of N. lugens resistance, even in a rice cultivar grown by the majority of farmers, to maintain low and stable N. lugens populations.

Five transgenic rice lines, each containing an insecticidal toxin gene from Bacillus thuringiensis (Bt) under control of a different promoter, were tested for effects on two non‐target insects: the brown planthopper, Nilaparvata lugens (Stål) (Homoptera: Delphacidae), and its predator Cyrtorhinus lividipennis (Hemiptera: Miridae). Bt toxin was detected by ELISA in the honeydew of N. lugens that fed on rice lines with the CaMV 35S and actin promoters. Nilaparvata lugens produced greater volumes of acidic honeydew (derived from xylem feeding) on all five Bt rice lines than on non‐transgenic control lines. The amount of honeydew derived from phloem feeding did not differ between Bt and control lines. There were no differences between N. lugens reared on Bt and control lines in any of the five fitness parameters measured (survival to the adult stage, male and female weight, and male and female developmental time). There were no differences between C. lividipennis reared on N. lugens nymphs from Bt and control lines, in any of the three fitness parameters examined (survival to the adult stage and male and female developmental time). Our results indicate that N. lugens and its natural enemies will be exposed to Bt toxins from rice lines transformed with some Bt gene constructs, but that this exposure might not affect N. lugens and C. lividipennis fitness.

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