PhD

Twenty locally available plants were screened for their antifeedant
activity against three important crop pests of Kerala using water,
acetone, benzene and petroleum other as extractants. Benzene was, in
general, the best extractant and as a test insect H. vigintioctopunctata
was more sensitive than S. litura or P. ricini. Among the twenty plants
screened all the extracts of C. infortunatum, A.indica, T.neriifolia and
E.odoratum and benzene and ether extracts of N.oleander gave high
leaf protection against H.vigintioctopunctata. Against S.litura benzene
and ether extracts of C.infortunatum, A.indica, T.neriifolia and
N.oleander were effective. Water extract of E.odoratum and acetone
extract of C.infortunaturm, A.indica and T.neriifolia also had high
antifeedant activity against S.litura. All extracts of A.indica and water,
benzene and acetone extract of N.oleander had antifeedant effect on
P.ricini.
High larval starvation was caused by most of the plant extracts which
showed antifeedant action. But some extracts ineffective as antifeedant
also caused high larval starvation.
Eight essential oils obtained from the country were screened for
feeding deterrency against P.ricini. Citronella oil, geranium oil and
camphor oil gave significant protection, but the dosages required were
too high to indicate possibilities of practical exploitation of essential
oils as antifeedants for pest control. Based on PC 95 values worked out
through bioassay studies using H.vigintioctopunctat as test insect
N.oleander ranked first as antifeedant. It was followed by
C.infortunatum, A.indica, T.neriifolia and N.odoratum. Based on
larval starvation these plants had different ranking.
Antifeedant activity of the extracts of T.neriifolia and N.oleander
persisted up to 22 days on brinjal on field while that of
C.infortunatum, E.odoratum and A.indica persisted up to 18 days. On
the basis of PT indices the treatments were ranked as water extract of
T.neriifolia > benzene extracts of N.oleander > C.infortunatum >
E.odoratum > A.indica.
The insecticidal effects of the plant extracts on D.cingulatus,
H.vigintioctopunctata and S.litura were low. However, extracts of
A.indica, T. neriifolia, P.odoratissimus and C.gigantea showed
significant toxicity to A.craccivora. But their LC 50 values ranged
from 34 to 93 per cent. Benzene extracts of C.infortunatum, A.indica,
T.neriifolia and E.odoratum had high systemic action on different
nymphal instars of D.cingulatus. Fourth instar nymphs were more
tolerant to the insecticidal action of the extracts.
The essential oils included in the experiment did not show insecticidal
activity on D.cingulatus and S.litura while some caused significant
mortality of A.craccivora at high doses.
Sixteen out of twenty plants tested had significant juvenomimetic
effect on D.cingulatus in one or more than one of the extracts tested.
When the different extracts were ranked on the basis of percentage of
normal adults and their sterility (an index of the possible build up of
the post treatment populations of the test insect) benzene was found to
be the best and it was followed by water while acetone and ether were
on par and far less effective. T.neriifolia, A.indica and E.odoratum
caused 100 per cent sterility of D.cingulatus in
water and benzene extracts and above 90 per cent sterility in other two
extracts. C.infortunatum and N.oleander caused 100 per cent sterility
in acetone, benzene and water extracts.
The juvenomimetic effect of S.litura was much lower than that on
D.cingulatus. All the extracts of A.indica and N.oleander, water and
acetone extracts of T.neriifolia and V.negundo, benzene and acetone
extracts of A.vesica, acetone extract of E.odoratum, ether extract of
M.esculenta and C.variegatum caused 100 per cent sterility to the
insect and hence the treatment would limit the contribution from the
treated insects to the next generation to zero level.
Bioassay studies showed that acetone extracts of C.infortunatum had
highest juvenilising effect on D.cingulatus. It was closely followed by
A.indica. T.neriifolia, N. oleander and E.odoratum were much less
effective than A.indica and C.infortunatum. Benzene extracts were
more active than acetone extracts and were ranked as A.indica >
C.infortunatum
>
N.oleander
>
E.odoratum
>
T.neriifolia.
Considering both the extracts C.infortunatum came on par with
A.indica. N.oleander and E.odoratum were also found promising.
The essential oils caused morphogenetic abnormalities in the
developing numphs of D.cingulatus. The dosage at which high sterility
could be obtained were too high to ensure economic viability of its use
in field. Lower effective dosages, cheaper and comparably effective oils
may have to be found out for wide use of essential oils for pest control.
Benzene
extracts
of
A.indica,
E.odoratum,
C.infortunatum,
T.neriifolia and N.oleander and water extracts of T.neriifolia as 2%
emulsions
reduced
the
populations
of
H.vigintioctopunctata,
C.insolitus and A.gossypii on brinjal and H.vigintioctopunctata on
bitterground significantly in the field experiments. All the treatments
(except T.neriifolia againist A.gossypii) came on par with the
insecticide check, carbaryl 0.2 per cent suspension, in reducing the
population. The studies have thus established that the antifeedant and
juvenoid effects of five plants screened out from the local flora were as
promising as those of A.indica, the well recognized plant source for
such activity and the extracts of these plants can be exploited
effectively in the integrated control of crop pests.