MSc

The magnitude and intensity of insect pest and their defenders at different growth
stages of rice were assessed in a survey during the virippu season of 1998, adopting
random sampling technique, in three taluks of Thiruvananthapuram district.
The survey revealed that the occurrence and distribution of the population of pests
and defenders were same in the various locations, where the tolerant variety Jyothi was
cultivated. The total population of pests and defenders observed at different growth stages
of the crop followed a definite pattern in the three locations.
Different concentrations of the leaf extracts of A. indica, and C. infortunatum and
nimbecidine were evaluated in the laboratory for their antifeedant and deterrent activity
and contact toxicity against important pests of rice and their defenders. Based on the
percentage of leaf protection, the plant products tested were superior to control against
C. medinalis. The same effect was noticed with N. depunctalis, only with the highest dose
of leaf extracts of A. indica and nimbecidine. Seventy five per cent deterrent effect was
observed to N. lugens at the highest dose of the plant products. None of the plant products
showed any deterrent action against L. acuta or exhibited contact toxicity to L. acuta,
C. medinalis. N. depunctalis andN. lugens. Both the defenders tested CL. pseudoannulata
and O. nigrofasciatay; were safe with the plant products.

2
Replicated experiment was conducted on rice to evaluate the efficacy of plant
products in suppressing the pests as well as in augmenting the defenders under field
conditions. The leaf extract of C. infortunatum was found to be efficient in suppressing
the population of C. medinalis. The effect was same as that with insecticides. The
population of N. depunctalis was reduced by the leaf extracts of A. indica and
C. infortunatum as observed in treatment with carbaryl. The suppressing effect
observed on N. lugens was same with both the leaf extracts and insecticides, whereas,
none of the treatments showed reduction in the population of L. acuta.
The total population of the pests in general, showed a varying effect of plant products
at different growth stages of the crop. Leaf extracts of C. infortunatum resulted in an
immediate suppression of the total population of the pest at 20 DAT, whereas, A. indica
gave significant reduction at 40 DAT. The treatments didnot show any effect on the total
pest population at 60 DAT.
The effect of plant products on spider population revealed that they were found to be
safe. The leaf extract of A. indica increased the spider population at 20 DAT and
C. infortunatum at 60 DAT, whereas, insecticides showed harmful effect up to three days
after application. Adverse effect with plant products on the population of 0. nigrofasciata
was not observed in any of the treatments. An increase in the population of the predator
was observed with leaf extracts of A. indica at 20 DAT and with C. infortunatum at 40 and
60 DAT. Significant reduction in the population of Agriocnemis spp. was recorded in
treatment with leaf extract of C. infortunatum, whereas, significantly higher population
was observed in treatment with leaf extract of A. indica. The population of M crocea was
reduced due to the application of plant products and the effect was retained up to three
days after application.




3
The influence of plant products on the total population of defenders has clearly
indicated that the leaf extracts of A. indica and C. infortunatum were safe to the defenders.
Based on the P:D ratio, these products were found to have the best effect in augmenting
the population of defenders and suppressing the population of pests. Significant differences
in the grain and straw yield was not recorded either in treatments with plant products or
with insecticides when compared with control.
Overall assessment of the results obtained revealed that A. indica and C. infortunatum
can be effectively and safely used for the management of important pests of rice with out
much adverse effect on non target organisms in the rice ecosystem. Just like A. indica,
C. infortunatum could also be utilised for developing effective plant protection chemicals
for replacing undesirable synthetic insecticides in integrated pest management.