20
Rice Brown Planthopper
Australia, towards Indonesia, Malaysia, and Indo-China region of Thailand, Laos,
Vietnam, Cambodia and probably Myanmar. During October to February monsoon
winds move in just reverse direction along the heating maxima which moves entirely
in southern hemisphere from indo-China region to southern tip of Indonesia. BPH is
likely to migrate in both the directions. As rice is cultivated throughout the year in the
entire region and due to lack of studies on long range migration of BPH in this region,
all this information is still hypothetical.
Process of BPH Long Distance Migration:
BPH can usually move few meters in the same field when disturbed. The insects can
fly few hundreds of meters to few kilometers from one rice crop area nearing harvest to
another area where young rice crop is available. This small distance movement or short
range migration or trivial migration involves the following steps (Kisimoto, 1976; 1984).
1. Movement of BPH (macropterous males and females) from plant base to the tip
of crop canopy either at dawn or at dusk when the wind speed is low (< 5m/
second)
2. Taking off into the blowing wind up to a few metres height (usually 5-15m)
3. Movement along the wind direction at this height for few meters to few
kilometers
4. Landing to the fresh sites by downward movement.
5. Establishing the population at the new site.
However, long-range migration of BPH, which involves the movement of insects for
few hundreds of kilometers up to even 2000kilometers, is entirely different. In this case
there will be mass movement of BPH usually in groups ranging from few thousands to
few lakhs at a time during unfavorable conditions. The insects move to the tip of crop
canopy either during dawn or dusk (Ohkubo & Kisimoto, 1971). From there, the insects
make a slow upward movement until they reach up to a height of 750 to 2000 meters
aboveground level (Riley et al., 1991). Then, BPH will be above the cloud-forming
zone of atmosphere. At this height, the insects are carried by forward movement of
frontal-zones of hot humid winds of the monsoon. The movement will occur at a wind
