16
Rice Brown Planthopper
areas of A.P., Karnataka, Tamil Nadu, Kerala, Orissa and West Bengal. WBPH,
however, continued to be important in Punjab, Haryana and Western Uttar Pradesh.
This situation continued up to the year2002-03. From 2005-06, there were sporadic
but large-scale occurrences of BPH in Bihar, Jharkhand, Uttar Pradesh, Haryana and
Punjab. From 2007-08onwards, BPH attained number one pest status in the entire Indo-
Gangetic belt stretching from West Bengal, Bihar, Jharkhand, Uttar Pradesh, Haryana
and Punjab, although, WBPH was present in low numbers (DRR, 2010).
Possible Reasons for Distinctness of South Asian BPH Biotype:
BPH existed in Indian subcontinent ever since rice cultivation was present in
this area, i.e. more than thousands of years ago. But BPH became notorious
only after green revolution with the cultivation of short statured, high N
responsive, high tillering varieties providing suitable microclimate. Therefore,
the distinctness of Indian BPH must have its genetic origin much before green
revolution era.
BPH in India might have undergone parallel evolution along with tropical
indica rice in hot humid tropical climate present in South India and Sri Lanka
the region to which most of the rice cultivation was confined. During these few
thousand years, the insect might not have had any genetic interchange with
the BPH present in East Asia and South East Asia. Therefore, it preserved its
genetically controlled virulence to some resistant genes in rice.
Many of the tall Indicas cultivated in India appeared to have possessed genes
with moderate level of resistance to BPH. These resistant cultivars might have
possibly exerted pressure on the insect to preserve its unique virulence.
The main southwest monsoon prevalent in Indian subcontinent, can never cross
Himalayas and move further north to China. Therefore, Himalayas appeared
to have acted as a natural barrier for preventing Indian BPH populations from
moving to China. During North-East monsoon from northern India BPH can
move up to Sri Lanka only. This might have prevented the insect moving
further south.
Only for the last 5-10 years, there appears to be long distance migration of BPH
