MSc

Monitoring of the incidence of pests and their
natural enemies was carried out in the heavily insecticide
sprayed vegetable cowpea plots in farmers' fields in two
locations viz. Kalliyoor and Palappur in Thiruvananthapuram
District and in the unsprayed crop raised in the Instructional
Farm, College of Agriculture, Vellayani, during kharif and
rabi, 1996.
The results of the monitoring revealed that the pea
aphid, A. craccivora , the pod bugs R. pedestris and C. gibbosa
and the pod borers H. armigera, L. boeticus and M. testulalis
were the major pests that attacked vegetable cowpea both in the
insecticide sprayed as well as in the unsprayed plots. The pea
aphid was persistent in the insecticide sprayed fields where as
in the unsprayed fields, they were not seen upto 35 days after
sowing, in both kharif and rabi season. The pod bugs and pod
borers were seen throughout the cropping period with increase
in the post flowering period in both sprayed and unsprayed
crop. Attack of the american serpentine leaf miner L. trifolii
was observed only in the insecticide sprayed fields and was
present in rabi as well as in the kharif seasons



The


parasitoids that


were


encountered


were



A. nigrotibiali$, Charops sp., Salius sp. and T. subvirescens

and the predators were M. sexmaculatus, M. crocea, Scyanus sp.,
E. stali, S. geminate and X. scutellarae. The population of
the natural enemies was higher during the rabi season than
that during kharif season.
The population of the pests and natural enemies in
the insecticide sprayed and unsprayed plots were compared using
students ‘t' test and the results revealed that the pest were
more in the un sprayed plots but the population was higher only
for a shorter period and it was effectively checked by the
natural enemies, the population of which synchronized with that
of the pests. There was significantly higher population of
natural enemies in the unsprayed plots when compared
to unsprayed plots.
The role of the green lacewing C. carnea in the
management of the vegetable cowpea pests was studied through
replicated field trials conducted at College of Agriculture,
Vellayani during 1996. The impact of biorationals viz., neem
oil and tobacco decoction and insecticide, malathion on the
predator C. carnea and in their effectiveness in management of
cowpea pests was also studied in the field experiment.
C. carnea released @ 50 per plot at fortnightly
intervals effectively checked the aphid population. Among the
botanicals, tobacco decoction 2 per cent was found to be
effective in controlling the aphids, pod bugs and pod borers.

Neem oil emulsion 10 per cent when applied at fortnightly
intervals was also found to be significantly superior to the
untreated control. However the infestation by aphids and the
pod bugs was' less in all the treatments when compared to
control. Though the control plot did not show significant
reduction in yield, the quality of the produce was reduced due
to the pest infestation. C. carnea @ 100 per plot at
fortnightly and monthly intervals were effective against pod
bugs. The pod borers were effectively checked by C. carnea •
50 arid 100 per plot. In general the monthly release of C.
carnea was comparatively less effective in controlling the
pests. The botanicals did not show any deleterious effect on
C. carnea.
When the yield was assessed in terms of weight and
number of pods harvested, significantly higher yield was
recorded only in plots treated with tobacco decoction 2 per
cent when compared to untreated control.