Niche partitioning of rice planthoppers and impact of elevated CO2 on brown planthopper (BPH) and predation potential of wolf spider
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Date
2017
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Division of Entomology ICAR-Indian Agricultural Research Institute New Delhi
Abstract
Niche partitioning between brown planhopper (BPH), Nilaparavata lugens
(Stal.) and whitebacked planhopper (WBPH), Sogatella furcifera (Horvath) was
studied in relation to different abiotic and biotic factors in early and late transplanted
crop of Pusa Basmati 1121 during kharif 2015 and 2016. Peak populations of BPH were
observed between 27-29 °C and 75-80% relative humidity (RH) during 62-82 days after
transplanting (DAT), when there were 2-3 predators /hill, while highest WBPH
population was recorded between 29-31°C and 75-80% RH during 42-52DAT with 1-
2 predators /hill during kharif 2015 and 2016. The WBPH occupied broader niche with
respect to microhabitat temperature, microhabitat relative humidity and crop phenology
in early and late transplanted crop during both 2015 and 2016 compared to BPH that
occupied narrower niche. However, BPH occupied broader niche with respect to
occupation of stem space and association with predators compared to WBPH during
the same period. The WBPH thus proved to be a generalistic species compared to BPH,
which acted as more specialist species as it occurred in higher number on rice crop for
a shorter period of time towards September-October months.
Effect of elevated CO2 on BPH population was analyzed under open top
chamber (OTC) at elevated CO2 (570 ± 25 ppm) compared to ambient CO2 (400 ± 25
ppm) during two cropping seasons, kharif 2015 and 2016. Elevated CO2 exhibited
positive effect on BPH multiplication that resulted in about doubling of its population
at peak incidence (120.2±14.7 hoppers /hill) than ambient CO2 (61.8±13.55 hoppers
/hill) during 2015. Similarly during 2016, BPH peak population under elevated CO2
was observed to be higher (149.2±22.95 hoppers /hill) than ambient CO2 (93.2±8.55
hoppers /hill). This higher BPH population under elevated CO2 perhaps could be
ascribed to higher brachypterous female population during the two years.
Elevated CO2 exhibited nutritive effect on uninfested rice plants through
increase in number of tillers /hill (14-21%), number of reproductive tillers /hill (17-
31%) and number of seeds /panicles (13-14.5%) that resulted in 6-8% increase in grain
yield compared to rice plant grown under ambient CO2. However, despite the nutritive
effect of elevated CO2, rice plants under elevated CO2 condition suffered higher yield
loss (30.6-31.7%) due to higher BPH population compared to plants grown under
ambient CO2 that had 17.7-18.5% yield loss.
Study on functional response of wolf spider, Pardosa pseudoannulata (Boesenberg
and Strand) in relation to different prey densities of 3rd and 4th instar BPH nymphs was
undertaken in glass jar arena and in microcosm. In jar arena, under ambient CO2
predator feeding rate increased from 5.5±0.5 to 16.7±3.1 hoppers/ predator with
increase of prey density from 10 to 50 hoppers /predator compared to feeding rate in
microcosm, where it increased from 4.0±0.8 to 11.0±3.4 hoppers /predator. Similarly,
in jar under elevated CO2 feeding rate (5.7±0.9 to 18.5±3.6 hoppers/ predator) was
higher than microcosm (4.4±0.7 to 12.6±3.9 hoppers/ predator). The feeding rate of the
spider in microcosm as well as in jar arena under elevated CO2 was slightly higher than
under ambient CO2 condition.
Based on predation study, number of attacked prey (Ha) and prey density per unit
area over a period of time (HT) were determined. Regression of 1/Ha on 1/HT in
microcosm and jar arena under ambient CO2 as well as elevated CO2 revealed
functional type II response of wolf spider on BPH nymph. The attack rate (0.48±0.02),
maximum attack rate (2.89±0.67) and efficiency parameters (0.36±0.09) of the predator
were higher but handling time was lower (1.15±0.25) in jar arena compared to attack
rate (0.28±0.03), maximum attack rate (1.46±0.44), efficiency parameters (0.15±0.05)
and handling time (2.76±1.18) in microcosm under ambient CO2. Similar trend was
also observed for all parameters under elevated CO2. Attack rate, maximum attack rate
and efficiency parameters were higher and handling time was lower in both jar arena
and microcosm under elevated CO2 compared to ambient CO2.
The impact of elevated CO2 (570±25 ppm) on protein level, and activity of
protective enzymes viz., catalase and peroxidase in rice plant and BPH individuals was
analyzed. The results showed that protein content in uninfested plants under elevated
CO2 was significantly reduced compared to ambient CO2, but the activity of protective
enzymes, such as catalase and peroxidase was significantly enhanced compared to
ambient CO2. In BPH infested rice plants, protein content and catalase activity were
reduced significantly at both elevated and ambient CO2 conditions compared to
uninfested rice plant. Insect feeding reduced protein content and catalase activity in
plants, thereby further increasing plant stress posed by elevated CO2. However, the
activity of peroxidase in infested rice plant significantly increased at both elevated and
Description
t-9646
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