RESPONSE OF Spodoptera exigua HUBNER (NOCTUIDAE : LEPIDOPTERA) ON CHICKPEA UNDER ELEVATED CO2 AND CONSTANT TEMPERATURES
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Date
2018
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Acharya N.G. Ranga Agricultural University
Abstract
Studies on ‘Response of Spodoptera exigua Hubner. (Noctuidae :
Lepidoptera) on chickpea under elevated CO2 and constant temperatures’ were
conducted during 2015-2017 at ICAR - Central Research Institute for Dryland
Agriculture (CRIDA), Hyderabad, Telangana. The growth and development of
four successive generations of S. exigua on chickpea grown under ambient CO2
(aCO2; 380 ± 25 ppm) and elevated CO2 (eCO2; 550 ± 25 ppm) conditions was
studied. Under elevated CO2 conditions the concentrations of nitrogen (9.16-22.35
%), amino acids (7.69-14.08 %) and proteins (5.73-13.22 %) were lower
compared to ambient CO2 conditions. But the concentrations of carbon (6.76-
12.22 %), C: N (17.53-44.58 %), tannins (23.77-35.00 %), total soluble sugars
(TSS) (19.23-29.75 %), starch (31.91-44.29 %) and carbohydrates (19.90-30.16
%) were higher under elevated CO2 conditions compared to that under ambient
CO2 conditions. As a result, S. exigua experienced a significant impact on its
growth and development resulting in more consumption of chickpea foliage
(25.21-32.10%), increased larval weight (4.75-8.37 %), decreased pupal weight
(2.59-6.52 %), extended larval duration (1-2 days) and reduced fecundity (5.68 -
13.30 %) in all the four successive generations compared to that under aCO2
conditions. Further, elevated CO2 conditions significantly altered the quality of the
chickpea foliage resulting in increased relative consumption rate (RCR, 5.60-6.75
%) and approximate digestibility (AD, 4.48-6.45 %) but decreased efficiency of
conversion of ingested food (ECI, 16.27-20.14 %), efficiency of conversion of
digested food (ECD, 19.92-24.12 %) and relative growth rate (RGR, 11.19-12.15
%) of S. exigua compared to those at aCO2 conditions across the four generations.
The potential number of larval individuals and total eggs laid by all
females under eCO2 conditions reduced by 11.33 per cent and 8.48 per cent in the
second generation, 26.39 per cent and 23.57 per cent in the third generation and
34.89 per cent and 41.71 per cent in the fourth generation, respectively. The
combined effect of higher larval mortality and lower fecundity under eCO2
conditions resulted in potential population consumption of S. exigua decreased by
7.45 per cent in the third generation and 26.47 per cent in the fourth generations,
respectively compared to aCO2 conditions. Potential population increase index
were reduced by 16.77 per cent in the second generation, 12.39 per cent in the
third generation and 13.03 per cent in the fourth generations under eCO2
compared to aCO2 conditions, respectively.
The durations of different growth stages and life table parameters of
S. exigua were studied at 20, 25, 27, 30, 33 and 35 °C temperatures under two
CO2 conditions. Developmental time of S. exigua (egg to adult) declined with
increase in temperature and was more evident under eCO2 conditions. Under
eCO2 conditions, the durations of egg (5.20 to 2.00 days), larva (24.60 to 9.45
days), pupa (15.45 to 5.60 days), adult (11.50 to 5.40 days) and total
developmental periods (56.75 to 22.45 days) decreased from 20 to 35 °C
temperature compared to aCO2 conditions. Intrinsic rate of increase (rm), finite
rate of increase (λ), net reproductive rate (Ro), gross reproductive rate (GRR) and
mean generation time (T) of S. exigua increased significantly with temperature
range of 27 - 33 °C and declined further with increase in temperature and showed
a non-linear relationship with temperature. Reduction of ‘T’ was observed from a
maximum of 49.52 days at 20 °C to a minimum 21.90 days at 35°C. The thermal
requirement of S. exigua from egg to adult (total development period) was 588.24
degree days under eCO2 as against 555.56 degree days under aCO2 conditions.
Under elevated CO2 conditions, chickpea plants exhibited lower nitrogen
levels due to increased photosynthesis resulted in poorer food quality for
S. exigua larvae leading to prolonged larval duration, lower pupal weight and
lower fecundity, increased food consumption and assimilation with reduced food
conversion efficiency by larvae and ultimately resulted in slow growth across four
generations.
Description
D5631
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