MSc

The study entitled “Management of pests of grain cowpea, (Vigna unguiculata
(L.) Walp.) using cashew nut shell liquid based botanical pesticide” was conducted at
Department of Agricultural Entomology, College of Agriculture, Vellayani and Krishi
Vigyan Kendra, Sadanandapuram, Kerala Agricultural University during 2019-2022 to
evaluate the efficacy of cashew nut shell liquid (CNSL) for the management of pests of
grain cowpea.
Laboratory evaluation of CNSL against pests and natural enemies of grain cowpea
was conducted using the treatments viz., CNSL 20% EC at 0.3, 0.5 and 1%, CNSL 20%
EC at 0.3 % followed by the application of Beauveria bassiana 2%, B. bassiana 2%
alone, chemical check, dimethoate 30 EC 0.05% and untreated control. The test insects
viz., pod bug, Riptortus pedestris Fabricius (both nymphs and adults) and syrphid fly
larvae (Paragus sp.) were used in the study. The trial was conducted with topical
application of CNSL on test insects and fed with treated and untreated food. In both the
methods, CNSL 20 % EC at 1% recorded significantly higher percentage mortality
throughout the observation period attaining cent per cent mortality at 96 hours after
treatment (HAT). In topical application of CNSL with untreated food, the percentage
mortality was comparatively low during the initial hours of treatment in lower
concentrations of CNSL viz., 0.3% (no mortality observed till 96 HAT) and 0.5% (0.00,
20.00, 40.00 and 40.00 respectively at 24, 48, 72 and 96 HAT) than the topical
application method with treated food. The corresponding mortality at 0.3 and 0.5% of
CNSL 20% EC was 0.00, 20.00, 40.00 and 100.00 per cent respectively at 24, 48, 72 and
96 HAT.
In the case of R. pedestris adults, the higher concentrations of CNSL 20 % EC at
0.5 and 1% attained cent per cent mortality at 4 days after treatment (DAT). No
significant difference was observed in the percentage mortality of R. pedestris adults
among different concentrations of CNSL (0.3, 0.5 and 1%) up to 3 DAT. Laboratory
evaluation of different treatments on syrphid fly larvae indicated the safety of CNSL
based treatments.
During the field evaluation, higher concentrations of CNSL 20 % EC at 0.5 and
1% significantly reduced the population of aphids, Aphis craccivora Koch and pod bugs,
R. pedestris as compared to other botanicals and untreated control during the vegetative
stage of the crop. A gradual reduction in the mean population of aphids was observed in
CNSL 20 % EC at 0.5 and 1% from 1 DAT to 7 DAT, but a hike in the population was
observed at 14 DAT. The values being 133.33, 93.33, 73.33 and 50.00 plant-1 in the case
of CNSL 20 % EC 0.5 % and 53.33, 43.33, 35.00 and 18.33 plant-1 with CNSL 20 % EC
1% respectively at 1, 3, 5 and 7 DAT and the mean population reached 96.67 and 66.67
plant-1 respectively at 14 DAT. More than 85 per cent reduction over untreated control
was noticed in CNSL 20 % EC 1% among the botanicals at all intervals after spraying.
No adverse effect of treatments was observed on the natural enemy population in the
field.
During the reproductive stage, all the CNSL containing treatments recorded more
than 80 % population reduction over untreated control from 1 DAT to 7 DAT and the
observation on the mean population of aphids indicated the efficacy of CNSL 20 % EC at
1% with a significantly lower population of aphids(43.33 plant-1) at 14 DAT. Regarding
pod bugs, the mean population at the pod formation stage was significantly low in the
plants treated with CNSL 20 % EC at 0.5 and 1% in all the observations and the values
being 5.33 and 4.00 plant-1, 2.67 and 2.00 plant-1, 1.00 and 0.33 plant-1 and 0.33 and 0.00
plant-1 at 1, 3, 5 and 7 DAT respectively. But at 14 DAT, though all the treatments
showed a slight increase in the population, CNSL containing treatments recorded
significantly lower population comparable to that of chemical check, dimethoate 30 EC
0.05% and resulted in a percentage reduction of more than 80.00 from 3 DAT onwards.
Application of CNSL 20 % EC at 1 and 0.5 % attained a higher yield of 29.17
and 26.77 g plant-1 and was on par with the chemical check, dimethoate 30 EC 0.05%
(30.00 g plant-1).
A laboratory trial was carried out to study the effect of CNSL on the storage pest,
Callosobruchus chinensis L. using cowpea seeds. Crushed cashew nut shell at 40 g/kg
seed showed very good repellency of C. chinensis and was seemed to be on par with
chemical check. At 24 HAT, cent percentage mortality of C. chinensis was recorded in
crude CNSL at 6 mL kg-1 seed and was significantly superior to chemical check. Crude
CNSL (2, 4 and 6 mL kg-1) as well as CNSL 20 % EC formulation (4 and 6 mL kg-1 seed)
recorded significantly higher mortality of C. chinensis when released to treated seeds at
48, 72 and 96 HAT. Oviposition, progeny emergence and grain damage was not observed
in any of the treatments except in seeds treated with crushed cashew nut shell at 20 g kg-1
seed with 46.67 eggs, 30.67 adults and 38.33 grains damaged. None of the treatments
adversely affected the germination of seeds, since cent percentage germination was
noticed in all the treatments except in chemical check (92.00 per cent) by 7 DAT.
However, the germination parameters viz., seedling length, seed vigour index and speed
of germination differed slightly among the treatments.
The efficacy of CNSL 20 % EC at 0.5 and 1% against A. craccivora and R.
pedestris were proved. Since crude CNSL and CNSL EC formulation were found equally
effective in managing C. chinensis when used as seed treatment, considering the
germination parameters, crude CNSL at 2 and 4 mL kg-1 seed as well as CNSL 20 % EC
at 4 and 6 mL kg-1 seed were found promising for seed treatment against bruchids.