MSc

Spodoptera litura Fab. (Lepidoptera: Noctuidae) is a polyphagous pest with
cosmopolitan distribution, causing severe defoliation in economically important
crops. The current management strategy for this pest relies heavily on blanket
spraying of insecticides which may not reach the target. Indiscriminate use of
pesticides indirectly affects various non-target organisms and also will lead to the
problems like resurgence, resistance and secondary pest outbreaks.
Baiting technique comprises an attractive food along with an insecticide to
lure insect pests and kill. The amount of insecticide active ingredient applied per
unit area with the use of bait is much lower than that of blanket insecticide sprays.
Hence, the present study was undertaken to identify a potential insecticidal bait for
the management of S. litura.
The study was conducted during 2017-2018 at the Department of Agricultural
Entomology, College of Horticulture Vellanikkara, Kerala Agricultural University,
Thrissur. In order to identify a base material preferred by S. litura, baits were
prepared by using different substrate, viz., rice bran, maize bran and wheat bran
along with jaggery and water. Mean consumption of bait by the S.litura larvae after
48h were recorded and results revealed superiority of bait containing wheat bran
and jaggery in 8:2 ratio, followed by maize bran. Spodoptera litura larvae
consumed 0.1980 g of wheat bran based bait in a period of 48 hours.
After screening the base material for bait the standardisation of
phagostimulants, such as yeast (1%), starch (0.2%), and coconut oil (1%) as an
additive to the bait to increase the attractiveness of bait was done. Bait containing
starch (0.2%) was found to be very attractive and resulted in doubling of the
consumption of bait (0.3842 g) in comparison to the control. Hence, wheat bran
based diet with starch (0.2%) was chosen for further studies.
Insecticides, viz., chlorpyriphos (20% EC), thiodicarb (75% WP), lambda
cyhalothrin (5% EC), fipronil (5% SC), spinosad (45% SC), emamectin benzoate
(5% SG), flubendiamide (39.35% SC) and chlorantraniliprole (18.5% SC) were
evaluated along with two microbials, NPV of S. litura (0.5% AS), and Bacillus
thuringiensis (5% WP). All the pesticides were evaluated at the doses viz., 25 per
cent, 50 per cent and 75 per cent of recommended dose. The results showed that
emamectin benzoate (5% SG), thiodicarb (75% WP) and chlorpyriphos (20% EC)
as superior poison baits which showed 100 per cent mortality at 25 % concentration
of recommended dose within 12 h. Fipronil 5% SC in 24 h (75% recommended
dose) and spinosad 45% SC in 48 h (75% recommended dose) also lead to cent per
cent mortality in the shortest time. The above five insecticides were chosen for the
evaluation of poison baits in field.
Poison baits were evaluated in field planted with cowpea (var. Anaswara).
The experiment was laid out in randomized block design and replicated thrice with
an absolute control (without bait) and a control plot (with unpoisoned bait). In order
to prevent the movement of larvae from one plot to another plot were separated by
polythene sheets. In each plot 5 plants were tagged, which were equally distributed
from the centre of the plot. Twenty five six day old larvae were released at the
centre of each plot. After 10 days defoliation was measured using leaf area meter.
Two regression equations were worked out for central leaf and side leaves of the
trifoliate leaf of cowpea. Initial leaf area was assessed by measuring the length and
breadth of the leaf and substituting the breadth of the leaf in the regression equation.
Observation on leaf defoliation revealed that in emamectin benzoate baited plots
consumption was very low (2.95 cm2/5 plants/plot) after 10 days of treatment
followed by thiodicarb (8.44 cm2/5 plants/plot), chlorpyriphos (12.38 cm2/5
plants/plot), fipronil (12.69 cm2/5 plants/plot) and spinosad (30.61 cm2/5
plants/plot). Poison baiting with insecticides was found to be beneficial in reducing
the damage caused by S. litura at levels lower than the recommended dose with
minimum disturbance to non-target organisms.