Insecticide Susceptibilities in Populations of Two Rice Planthoppers, Nilaparvata Lugens and Sogatella Furcifera, Immigrating into Japan in the Period 2005-2012

Background: The brown planthopper Nilaparvata lugens and the whitebacked planthopper Sogatella furcifera are both important pests on rice throughout Asia. The major cause of recent outbreaks is thought to be the development of insecticide resistance. Thus, the authors monitored insecticide susceptibilities in populations of these two insects immigrating into Japan in the period 2005-2012. Ten insecticides were tested, including members of the organophosphate, carbamate, pyrethroid, neonicotinoid and phenylpyrazole groups.

Results: The LD50 values of N. lugens against imidacloprid increased from 2005 (0.7 µg g(-1)) to 2012 (98.5 µg g(-1)). The resistance ratio (LD50 value in 2012/baseline LD50 value in 1992) was 615.5. In contrast, LD50 values of N. lugens against fipronil were <1.0 µg g(-1) up to 2012, suggesting that N. lugens had developed no insecticide resistance to this insecticide. However, S. furcifera exhibited resistance against fipronil up to 2012. Except for the case of malathion, the resistances of N. lugens against members of the organophosphate and carbamate groups were closely similar in the period 2005-2012 to earlier determinations in 1984 and 1985.

Conclusion: 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.