MSc

The magnitude and intensity of leaf roller complex and natural
enemies at different growth stages of the rice crop were assessed in a
survey conducted during Mundakan season of 2002, adopting random
sampling technique in Kalliyoor panchayat of Thiruvananthapuram
district.
The survey revealed the occurrence of two different species of leaf
roller viz., Cnaphalocrocis medinalis (Guenee) and Marasmia patnafis
(Bradley). The distribution pattern of these two species in the n ce
ecosystem varied. C. medinalis had a population peak during the
vegetative stage and showed a gradual decline as the crop growth
progressed, whereas, M. patnalis had a population peak during the early
reproductive stage compared to vegetative and late reproductive stage.
The natural enemies recorded from the rice ecosystem incl ude three
parasites and ten predators. The distribution of natural enemies in the rice
ecosystem revealed that the population of parasites and predators showed
a gradual increase from vegetative to reproductive phase.
From the field experiment, it was evident that the synthetic
insecticides alone and botanicals + half dose synthetic insecticides were
efficient in suppressing the pbpulation of rice leaf roller. The treatments
with botanicals alone did not show any significant reduction in the
population of leaf roller compared to control.
G. tr iangulifer, a specific larval parasite of rice leaf roller, was
unaffected by the botanicals, synthetic insecticides and their combinations
at 30 OAT. In the case of X flavolineata and Cot esia sp., only an initial
suppression was noticed in insecticide included treatments. Later it was
found to be safe. All these treatments were found to be relatively safe to
predatory beetles. But Agriocnemis sp., spiders, predatory bugs and

Conocephalus sp. was adversely affected by the insecticide included
treatments. Botanicals were safe to all the natural enemies observed but
they were ineffective against rice leaf roller. The yield obtained was also
the highest in synthetic insecticides alone and botanicals + half dose of
synthetic insecticide treatments and were on par.
Overall assessment of the results obtained revealed that synthetic
insecticides alone and botanicals + half dose of synthetic insecticides were
equally effective in controlling rice leaf roller and safe to its specific
parasites and predators. For other natural enemies, it showed a varying
trend. In some cases there was an initial suppression and then
recolonization occurred. From this result, it was clear that botanicals +
half dose synthetic insecticides were as equally effective as full dose of
synthetic insecticides in suppressing the pest and in protecting natural
enemies. Hence we can substitute the full dose of synthetic insecticides
with combination of botanicals (either NSO three per cent or azadirachtin
0.004 per cent) and half dose of synthetic insecticides (either quinalphos
0.0025 per cent or imidacloprid 0.0025 per cent) for an ecofriendly
management of rice leaf roller.