118 M. Chandrashekharaiah et al.
above compounds on eggs, larvae, and adults
was evaluated under laboratory conditions.
The potential effect of CdS, Nano-Ag, and
Nano-TiO2 nanoparticles was evaluated on S.
litura. The preparation of the nanoparticles was
as per Chakravarthy et al. (2012b). Serial dilu-
tions from 150 to 2400 ppm were prepared in
the geometric order. The nanoparticle suspen-
sions were then subjected to ultrasonication.
Ten, second instar larvae were released on the
castor leaf discs (4 × 4 cm) treated with desired
concentrations of the solutions of nanoparticles
(leaf dip method bioassay technique). Each leaf
disc served as replicate, 3 per treatment and
leaf discs treated with water served as control.
The larvae after release on the castor leaf discs
were incubated at 25 ± 1 ̊C with a specific 70 %
relative humidity (RH) in a BOD incubator. The
numbers of larvae killed were recorded at 24 h
intervals up to 9 days and the percent larval mor-
tality was computed.
An attempt was also made to evaluate the
effect of tebufenozide (RH-5992) against fruit
borer, H. armigera. A stock solution of tebufe-
nozide (RH-5992) in acetone was first made,
from which the different test concentrations were
prepared and dispensed with the synthetic diet.
Neonate larvae were fed on diet treated with
tebufenozide at 0.01, 0.25, 0.50, 1.00, 2.50, and
5.00 ppm for 96 h. The fourth instar larvae were
fed on diet treated with 1.00, 2.50, 5.00, 10.00,
and 20.00 ppm of tebufenozide for 96 h. Tebufe-
nozide was dissolved in acetone and thoroughly
mixed with the diet and control diet treated with
acetone alone was kept for allowing it to evapo-
rate. The synthetic diet was prepared according
to Nagarkatti and Prakask ( 1974 ). Each experi-
ment was replicated five times with 50 larvae per
replicate. All data recorded from the experiments
were analyzed using software package R. version
2.10.0 (R development Core Team 2008 ) for sta-
tistical analysis.
Observations on developmental processes,
behavior and mortality were recorded on the lar-
vae till adults emerged. Histopathological obser-
vations: newly born and fourth instar larvae of H.
armigera reared in laboratory were utilized for
histopathological study. Treated and untreated
group of larvae were fixed in Bovin’s solution
overnight and rinsed in 70 % ethanol four times
prior to dehydration. The newly and fourth in-
star larvae were embedded in paraffin and cross
sections (4–6 μm thickness) were stained with
haematoxvlin-eosi. Cross sections of midgut of
untreated (control) larvae were also examined
under the microscope.Results
Effect of DNA-Tagged Nanogold Against
Spodoptera litura Fab.
As the concentration and days after treatment
increased, the larval mortality of second in-
star S. litura larvae also increased significantly
( p < 0.05). The maximum mortality of 30.0,
57.5, and 75.0 was observed at 500 ppm on
3rd, 4th, and 5th day, respectively (Table 1 ).
DNA-tagged gold nanoparticle has a devastat-
ing effect on the larval tissue of S. litura. These
metal nanoparticles were the better alternative
to synthetic insecticides, in addition to being a
toxicant that inhibits the biological and physi-
ological systems of insects (Biju 2007 ). The
high binding affinity of noble metals (e.g., gold)
for proteins is well documented (Joshi et al.Table 1 Effect of different concentrations of DNA-
tagged gold nanoparticle on second instar S. litura 3, 4,
and 5 days after treatment
Treatment
(ppm)
Percentage of larval mortality days after
treatmenta
3rd 4th 5th
200 10.0 (16.0)b 27.5 (31.4)c 35.0 (36.0)b
300 22.5 (28.2)a 42.5 (40.7)b 62.5 (52.3)a
400 25.0 (29.7)a 55.0 (47.9)ab 72.5 (58.6)a
500 30.0 (33.2)a 57.5 (49.6)a 75.0 (60.5)a
Control 0.0 (0.6)c 0.0 (0.6)d 0.0 (0.6)c
SEM ± 2.92 2.87 3.05
CD at 5 % 8.81 8.66 9.20
a Mean of 30 larvae/replication/treatment; figures in the
parentheses are angular transformed values; means fol-
lowed by same letters in each column are not signifi-
cantly different by LSD at 5 %