The three rice planthoppers: the brown planthopper (BPH), Nilaparvata lugens, the whitebacked
planthopper (WBPH), Sogatella furcifera, and the small brown planthopper (SBPH), Laodelphax
striatellus, are serious pests of rice throughout Asia. The northern limit of continuously breeding
populations of BPH and WBPH is located around the Red River Delta in Vietnam and Hainan Island in
China, where rice, their only host plant, is cultivated all year round. Neither of the two species is able to
overwinter successfully in temperate areas (Japan, Korea, and most areas of China), and colonization
occurs annually following long-distance migration from the overwintering areas. Thus, occurrence of
these two species of rice planthoppers in temperate areas is highly dependent on populations in the
overwintering areas. In contrast, SBPH is able to overwinter in the temperate zone of East Asia, including
Japan and China. SBPH transmits the Rice stripe virus to rice plants, which causes rice stripe disease.
To achieve high-precision migration prediction for BPH and WBPH, a real-time prediction system was
developed (Otuka et al., 2005, 2006; Furuno et al., 2005). In this system, the latest meteorological data are
supplied online to an advanced numerical weather prediction model, MM5. The model forecasts
3-dimensional atmospheric fields at one-hour intervals. In these fields, a planthopper migration simulation
model, GEARN, calculates movement of a number of modeled planthoppers and predicts their relative
aerial density at three-hour intervals. The results are converted to maps and are available on the web
(http://agri.narc.affrc.go.jp/) since 2004. The maps of relative aerial density provide information about the
timing and area of migrations over the next two days.
SBPH were believed to be largely indigenous, unlike migratory rice planthoppers such as BPH and
WBPH. However, recent shift of rice cultivars from hybrid rice to japonica varieties those were susceptible
to SBPH in eastern China caused outbreaks of this species and its density peaked in 2005. Consequently,
overseas migrations in early June started to appear in East Asia (Otuka et al., 2010; Syobu et al., 2011).
To estimate possible immigrations in advance, a new prediction method for the overseas migration of
SBPH from eastern China to Japan and Korea has been developed (Otuka et al., 2012). The method
consists of two techniques: estimation of emigration period in the source region and migration simulation.
The emigration period was estimated with the calculation of effective accumulated temperature for the
insect using real-time daily surface temperatures in the source areas. During the emigration period,
migration simulations were performed two times a day, or at every dawn and dusk. The prediction method
was evaluated with a cross-validation technique against four-year events from 2008 to 2011. The result
showed that the emigration periods included the mass migration events in 2008, 09 and 11 as well as an
emigration peak in the source in 2010. The method was successfully predicted those events.
Since 2005, outbreaks of BPH and WBPH have occurred in East Asian countries such as Vietnam,
China, and Japan. Outbreaks of SBPH have also occurred in eastern China and western Japan since mid-
2000s. These outbreaks are closely related to the development of insecticide resistance in the populations
in these regions. Thus, insecticide susceptibilities in BPH, WBPH, and SBPH collected from East and
Southeast Asian countries were determined and compared.
Insecticide susceptibility in BPH and WBPH was evaluated by a topical application method on insects
collected from East Asia (Japan, China, and Taiwan), Vietnam, and Philippines (Matsumura et al., 2008).
Species-specific changes in insecticide susceptibility were identified: imidacloprid resistance in BPH and
fipronil resistance in WBPH. Topical LD50 values for imidacloprid in the BPH populations collected from
East Asia and Vietnam were significantly higher than those from the Philippines, suggesting that resistance
to imidacloprid has developed in BPH in East Asia and Vietnam, but not in the Philippines. In contrast,
almost all the WBPH populations had extremely large LD50 values for fipronil, suggesting that resistance
to this insecticide is widespread in WBPH populations across East and Southeast Asia. Insecticide resistance of southern Vietnam against imidacloprid is higher than those of northern Vietnam and east
Asian, and is increasing from 2006 to 2010 (Matsumura et al., 2008; Matsumura & Sanada-Morimura,
2010; Matsumura et al., unpublished).
The insecticide susceptibility of SBPH was also evaluated using insects collected in East Asia and
Vietnam from 2006 to 2008. The SBPH populations in Jiangsu Province, China showed resistance only to
imidacloprid, whereas populations collected from western Japan showed resistance only to fipronil. In
contrast, the populations in China (Fujian Province), Taiwan, and Vietnam were highly susceptible to both
imidacloprid and fipronil. These results suggest that area-specific insecticide resistance has developed in
East Asian SBPH.
SBPH populations were believed to be largely indigenous, unlike migratory rice planthoppers such as
BPH and WBPH. However, traps in western Kyushu, Japan recorded large catches of SBPH in early June,
2008. A backward trajectory analysis indicated that the migration source was probably Jiangsu Province,
China (Otuka et al., 2010). The insecticide susceptibilities of populations collected in rice fields of western
Kyushu before and after the trapping period, and the presumed migration source region (Jiangsu) were
determined and compared. Both the Chinese and migrant populations showed resistance only to
imidacloprid, whereas the Japanese local populations collected before the trap catch showed resistance
only to fipronil. Because SBPH is able to overwinter successfully in Japan, it is feasible that intercrossing
between immigrant and domestic populations produces different characteristics in insecticide resistance
in local populations in Japan. Indeed, some SBPH populations in western Japan developed insecticide
resistance to both imidacloprid and fipronil after 2009 (Sanada-Morimura et al., 2011). This may be a
typical example of insect migration from an overseas population altering the insecticide resistance of local
(domestic) populations of SBPH.