21
Rice Brown Planthopper
speed of 5-20 m/sec. In this manner, BPH can move for about 25-45 hours to reach a
destination, which is about 800 to 2000 km away. What environmental, physiological
and behavioral factors determine the exact landing of the migrating insects is not very
clearly understood even today. The physiological factors like exhaustion of reserve
body energy or behavioral factors like oriented downward movement due to some
environmental stimulus like humidity gradient or light source on the surface of the
earth might be playing a role (Kisimoto, 1976, 1984).
Consequence of BPH Migration on its management:
In Indian sub-continent, BPH populations present in Sri Lanka and southern states of
India, viz. Kerala, Karnataka, Tamil Nadu and Andhra Pradesh and those present in
eastern states like Orissa, Chhattisgarh and West Bengal might be migrating to Uttar
Pradesh, Punjab and Haryana. Consequently, there is every likely-hood for genetic mixing
of BPH populations present throughout the Indian sub-continent including Sri Lanka,
Bangladesh and Pakistan. Similarly in case of East Asian biotype moving from China
to Japan and Korea also, genetic mixing exists. This has tremendous implications on the
management of BPH both in the origin and destination areas of long range migration.
For varied and obvious reasons, insecticides are extensively used for BPH management
throughout Asian countries where this pest is a major menace. When an effective
insecticide is extensively used in any area and the population develops high level
of resistance against that particular insecticide, then that insecticide or the other
insecticides with similar mode of action will be partially or completely ineffective in
almost all the areas where that particular biotype migrates. This type of situation has
already arisen with regard to resistance to imidacloprid a neonicotinoid in regions of
south Asian and east Asian biotypes. Similar can be the case with regard to resistant
varieties. When a resistant variety is released and extensively cultivated in one or
two areas and BPH develops virulence against that particular variety rendering it
susceptible. This can be extended to other varieties with similar genetic make-up with
regard to BPH resistance in the entire region, where that biotype occupies through long
range migration. This may not be evident in a short period like one or two seasons
but can be clearly seen after few years. This type of situation has already come to the
surface in case of IR26 with BPH-1 resistance gene in East Asian and south-east Asian
biotype existing regions.
