Diversity and Management of Insect pests in Bt and non-Bt cotton
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Date
2018
Authors
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Journal ISSN
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Publisher
MPUAT, Udaipur
Abstract
Diversity and management of insect pests in Bt and non-Bt cotton
Anusha Surakasula* Dr. R.
Swaminathan* Investigations on “Diversity and management of insect pests in Bt and non-Bt
cotton” were carried out in the Department of Entomology, Rajasthan College of
Agriculture, MPUAT, Udaipur, during the kharif seasons 2015 and 2016 with a view
to record the comparative seasonal incidence of major insect pests; estimate the
occurrence and diversity of associated natural enemies; and evaluate insecticide
schedules to manage the insect pests in Bt and non-Bt cotton. The major insect pests
comprised the sap feeding guild: aphids, jassids/ leaf hoppers, thrips and whiteflies as
major, while mealy bugs, the red and dusky cotton bugs as minor pests. Infestation by
aphids, leaf hoppers, thrips and whiteflies initiated from third week of June to first
week of July. The aphid population reached a peak in the last week of September
during kharif 2015 and 2016; whereas, leafhopper, thrips and whiteflies attained the
peak population in the third to last week of August. The mealy bug, red and dusky
* Ph. D. Scholar, Department of Entomology, Rajasthan College of Agriculture, MPUAT, Udaipur.
** Professor , Department of Entomology, Rajasthan College of Agriculture, MPUAT, Udaipur
cotton bugs appeared in the later part of the crop growth period in both years. The leaf
hopper population evinced a significant positive correlation with relative humidity in
Bt and non-Bt cotton; likewise, the population of thrips (in Bt and non-Bt cotton) and
whiteflies (Bt and non-Bt cotton) showed a significant positive correlation with
relative humidity. The populations of leaf hopper (Bt and non-Bt cotton) and thrips (Bt
cotton) had a significant positive correlation with the mean atmospheric temperature
during kharif 2016. Leaf hopper population had a significant negative correlation with
the hours of sunshine in both Bt and non-Bt cotton.
The more common natural enemies included coccinellids, spiders and syrphid
larvae that were relatively more in the month of September (Bt and non-Bt cotton)
during both the crop seasons. Mantid population was high during September (kharif
2015) and October (kharif 2016) in Bt and non-Bt cotton. The coccinellid population
showed a significant positive correlation with relative humidity in non-Bt cotton
during 2015. During kharif 2016, the syrphid larval population exhibited a significant
positive correlation with the mean atmospheric temperature in Bt and non-Bt cotton.
The aphidiphagous coccinellids and syrphid larval population showed a
significant positive correlation with the aphid population during both seasons in Bt
(r=0.830 and 0.796 during kharif 2015; r=0.781 and 0.911 during kharif 2016) and
non-Bt cotton (r=0.697 and 0.725 during kharif 2015; r=0.807 and 0.937 during kharif
2016) depicting a density-dependent predator-prey activity.
During both the crop seasons (kharif 2015 and 2016), among the insect pests
the relative density was the maximum for aphids (48.26 and 35.58 % in Bt cotton &
39.28 and 12.48 % in non-Bt cotton); among the natural enemies it was the maximum
for coccinellids (54.99 and 59.36 % in Bt cotton & 59.64 and 62.11 % in non-Bt
cotton). The indices of diversity, Shannon and Simpson, were relatively more for
insect pests in non-Bt cotton; whereas, for the natural enemies in Bt cotton.
In Bt cotton, imidacloprid 17.8 SL (200 ml/ha) significantly reduced the
populations of aphids (up to 85.61% in 2015 & 86.25% in 2016) and whiteflies (up to
73.18% in 2015 & 73.38% in 2016) after first spray; whereas, fipronil 70 WG (100
g/ha) was significantly effective in reducing the populations of leafhoppers (up to
76.98% in 2015 & 80.59% in 2016) and thrips (up to 81.28% in 2015 & 80.14% in
2016); however, after the second spray, imidacloprid 17.8 SL (200 ml/ha) showed a
significant reduction in the population of aphids (up to 76.52% in 2015 & 73.43% in
2016), leaf hoppers (up to 75.35% in 2015 & 80.33% in 2016), thrips (up to 71.06% in
2015 & 73.31% in 2016) and whiteflies (up to 72.66% in 2015 & 76.44% in 2016). In
non-Bt cotton, after the first and second spray, imidacloprid 17.8 SL (200 ml/ha) was
effective in reducing aphids (first spray: up to 80.89% in 2015 & 82.09% in 2016;
second spray: up to 76.21% in 2015 & 74.40% in 2016), leafhoppers (first spray: up to
83.63% in 2015 & 80.39% in 2016; second spray: up to 78.01% in 2015 & 77.51% in
2016), thrips (first spray: up to 75.92% in 2015 & 78.58% in 2016; second spray: up to
75.36% in 2015 & 72.90% in 2016) and whiteflies (first spray: up to 78.42% in 2015
& 77.22% in 2016; second spray: up to 71.61% in 2015 & 75.56% in 2016). In Bt
cotton, the spray schedule comprising imidacloprid 17.8 SL (200 ml/ ha) followed by
neem oil (3%) gave the maximum mean kapas yield of 2885 & 3048 kg/ha in 2015 &
2016, respectively; whereas in non-Bt cotton, imidacloprid 17.8 SL (200 ml/ ha)
followed by imidacloprid 17.8 SL (200 ml/ ha) recorded the corresponding maximum
mean kapas yield of 2300 & 2381 kg/ ha and C: B ratio of 1: 1.35 & 1: 1.36. However,
the C: B ratio of Bt cotton was maximum for neem leaf extract (5%) followed by
thiamethoxam 25 WG (100 g/ha) i.e., 1: 1.24 in 2015, and fipronil 70 WG (100 g/ha)
followed by neem leaf extract (5%) i.e., 1: 1.23 in 2016.
Description
Diversity Management Insect pests Bt non-Bt cotton
Keywords
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Citation
Surakasula. A, and Swaminathan. R.