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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.

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.

Spiroplasma-mediated late male killing was found in the small brown planthopper, Laodelphax striatellus. Female-biased colonies (maternal lines, N = 4) were established from planthoppers collected in Taiwan and Japan. This sex ratio distortion was maternally inherited (sex ratio of total number of progenies [female:male]: 488:0 in F1, 198:7 in F2, 407:0 in F3; likelihood ratio test of all generations, P < 0.0001) and caused by male death during nymphal stages. The female-biased colonies were doubly infected with Spiroplasma and Wolbachia, and the non-biased colonies were infected solely with Wolbachia. Antibiotic treatment resulted in a normal sex ratio, strongly suggesting that bacteria are manipulating host reproduction. Spiroplasma-singly-infected planthopper colonies created by the antibiotic treatment produced progeny with strongly female-biased sex ratios (181:2; likelihood ratio test, χ(2) = 231.6, P < 0.0001). This is the first report of Spiroplasma-mediated male killing in hemimetabolous insects.

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