PLANT MEDIATED SYNTHESIS OF SILVER NANOPARTICLES AND THEIR EFFICACY AGAINST CERTAIN SUCKING PESTS
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Date
2019-09
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Abstract
Experiments were carried out in the Department of Entomology and Plant Pathology, Assam Agricultural University, Jorhat during 2017-18 and 2018-19 to study the efficacy of plant mediated synthesized silver nanoparticles against certain sucking pests. The silver nanoparticles were successfully synthesized by using plant extracts such as Tulsi (Ocimum sanctum), Bakul (Mimusops elengi), Garlic (Allium sativum) and Posotia (Vitex negundo). The synthesized silver nanoparticles were characterized by UV-Vis spectrophotometer, Zeta sizer, Fourier Transform Infrared Spectroscopy (FTIR) and Transmission Electron Microscopy (TEM). The UV-Vis spectra recorded peak at 425 nm, 427nm, 420 nm and 430 nm for Tulsi, Bakul, Garlic and Posotia AgNPs, respectively. FT-IR analysis for Tulsi, Bakul, Garlic and Posotia AgNPs showed strong peaks at ranges of 400-4000 cm-1 which exhibited different types of functional groups viz., (O-H, C-H, N-H, H-H and C-C). Zeta potential was determined and recorded the charge of green synthesized silver nanoparticles as -24.2, -24.1, -16.7 and -33.0 mV for Tulsi, Bakul, Garlic and Posotia, respectively. TEM study revealed that the synthesized silver nanoparticles from different plant extracts were spherical and circular in morphology and the average size of 8 to 25 nm. The efficacy of plant mediated synthesized silver nanoparticles against mustard aphid (Lipaphis erysimi), papaya mealybug (Paracoccus marginatus), rugose spiralling whitefly (Aleurodicus rugioperculatus) and two spotted spider mite (Tetranychus urticae) was investigated in the dilutions of 100, 200, 300, 400 and 500 ppm. Nanoparticles obtained from Tulsi were found to be effective against L. erysimi and A. rugioperculatus for both the years 2017-18 and 2018-19 with nymphal mortality of L. erysimi (88.89% and 84.44%) and A. rugioperculatus (86.67% and 84.44%) after the fifth day of treatment. Nanoparticles extracted from Garlic were found to be effective against P. marginatus with 84.44% and 82.22% nymphal mortality for the year 2017-18 and 2018-19. Incase of T. urticae, nanoparticles extracted from Garlic showed the highest mortality of 73.33% and 77.78% for the year 2017-18 and 2018-19, respectively. The LC50 was estimated for all the tested sucking pests against all the synthesized AgNPs in 2017-18 and 2018-19. For L. erysimi the lowest value was calculated from Tulsi AgNPs after the fifth day of treatment for both the years 2017-18 and 2018-19, recorded 119.12 ppm and 109.76 ppm, respectively. For P. marginatus,
lowest LC50 of 109.21 ppm was recorded from Garlic AgNPs after the fifth day of the
treatment during 2017-18. In 2018-19 also the lowest LC50 value 116.33 ppm was
obtained from Garlic AgNPs. For A. rugioperculatus, the lowest LC50 from Tulsi
AgNPs was found to be 123.12 ppm during 2017-18 and in 2018-19 also Tulsi AgNPs
showed the lowest LC50 value of 139.27 ppm. For T. urticae the lowest value was
calculated from Garlic AgNPs after the fifth day of treatment for both the years 2017-18
and 2018-19, recorded 142.57 ppm and 130.39 ppm, respectively.
Behavioural changes in selected pests have also been noticed after
treating with synthesized silver nanoparticles for both the years 2017-18 and 2018-19.
For L. erysimi, the movement became slower, decreased feeding activity and colour
changed to brown-black, paralysed, body contents became dry and subsequently death.
After application of AgNPs on the eggs of P. marginatus, the colour changed to light
orange to dark brown and did not hatch. The neonate crawlers die within 2-3 days after
spray, survival was zero in some replicated plates, deformed and swelled body, sluggish
if touched brown liquid ooze out. The cream colour changed to dark brown which was
often died. For A. rugioperculatus the viability of eggs reduced and nymphs changed
their colour from light cream to dark brown and die soon. While incase of T. urticae,
legs became folded, move only when it disturbed, body contents come out and dry on
the 5th day of post spray.
In the pot experiments with biosynthesized AgNPs against L. erysimi
showed the highest per cent reduction by Tulsi AgNPs (79.40%) and the least per cent
reduction was observed with Posotia AgNPs (61.55%). For P. marginatus, Garlic
AgNPs was highly toxic as this caused 58.40% reduction at one day after spraying
which was increased to 75.17% after 5 days of spraying. Among different
biosynthesized AgNPs, Garlic AgNPs was found to be most effective against T. urticae
population which resulted in 69.33% reduction in 5 days after application in potted
plants.