priciples of insecticide use in rice ipm

Insecticides in Rice IPM (DRR)
MANAGEMENT OF GREEN LEAFHOPPER, VECTOR
OF RICE TUNGRO DISEASE WITH INSECTICIDES
In India, two species of green leafhoppers viz., Nephoteitix virescens and Nephottetix nigropictus act as
vectors of the most important viral disease of rice namely rice tungro disease (RTD). The main host plant
for Nephotettix virescens is rice, although, it can also survive on many grassy weed hosts. For Nephotettix
nigropictus, the grass, Leersia hexandra is the main host and rice is only an alternate host although it can
feed and multiply on rice.
RTD is caused by two types of viral particles viz., rice tungro bacilliform virus (RTBV) and rice tungro
spherical virus (RTSV) particles. The presence of both the particles in the host plant, rice causes the full
expression of the symptoms of RTD. The presence of only RTSV cannot express any symptom, while the
presence of only RTBV may produce mild symptoms. However, the presence of RTSV is very much essential
for acquisition and transmission of the disease from one plant to another.
TRANSMISSION OF THE RTD BY VECTOR
The viral particles causing RTD are stylet-born in nature and are present only in the stylet of GLH. When
a viruliferous insect starts feeding on the healthy host, the RTBV and RTSV are transmitted to the plant.
The virus particles do not multiply in the body of the vector. Both the nymphs and adults of GLH are
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GLH Adults RTD Infected field
capable of transmitting RTD but in nymphs the virus particles are lost along with the exuvae at the time of
moulting. Hence, the acquisition of the virus is essential after moulting for the vector to become viruliferous.
In case of adults, the virus is transmitted until the inoculum gets exhausted in the stylet of GLH. The
acquisition period i.e. the minimum period of feeding required for the vector to acquire the virus from
diseased plant, in case of RTD, is approximately 6 hours. The transmission period i.e. the minimum time
of feeding required for the viruliferous vector to transmit the viral particles into a healthy host is only 1-
2 minutes in case of RTD. The viruliferous vector after acquiring the virus can transmit the disease upto
about 3 days without further acquisition.