Temperature Impacts the Development and Survival of Common Cutworm (Spodoptera litura): Simulation and Visualization of Potential Population Growth in India under Warmer Temperatures through Life Cycle Modelling and Spatial Mapping.

The common cutworm, Spodoptera litura, has become a major pest of soybean (Glycine max) throughout its Indian range. With a changing climate, there is the potential for this insect to become an increasingly severe pest in certain regions due to increased habitat suitability. To examine this possibility, we developed temperature-based phenology model for S. litura, by constructing thermal reaction norms for cohorts of single life stages, at both constant and fluctuating temperatures within the ecologically relevant range (15-38°C) for its development. Life table parameters were estimated stochastically using cohort updating and rate summation approach. The model was implemented in the geographic information system to examine the potential future pest status of S. litura using temperature change projections from SRES A1B climate change scenario for the year 2050. The changes were visualized by means of three spatial indices demonstrating the risks for establishment, number of generations per year and pest abundance according to the temperature conditions. The results revealed that the development rate as a function of temperature increased linearly for all the immature stages of S. litura until approximately 34-36°C, after which it became non-linear. The extreme temperature of 38°C was found lethal to larval and pupal stages of S. litura wherein no development to the next stage occurred. Females could lay no eggs at the extreme low (15°C) and high (> 35°C) test temperatures, demonstrating the importance of optimum temperature in determining the suitability of climate for the mating and reproduction in S. litura. The risk mapping predicts that due to temperature increase under future climate change, much of the soybean areas in Indian states like Madhya Pradesh, Maharashtra and Rajasthan, will become suitable for S. litura establishment and increased pest activity, indicating the expansion of the suitable and favourable areas over time. This has serious implication in terms of soybean production since these areas produce approximately 95% of the total soybeans in India. As the present model results are based on temperature only, and the effects of other abiotic and biotic factors determining the pest population dynamics were excluded, it presents only the potential population growth parameters for S. litura. However, if combined with the field observations, the model results could certainly contribute to gaining insight into the field dynamics of S. litura

Assessing Impact of Projected Climate Change on Sali Rice in a Representative District of Upper Brahmaputra Valley Zone of Assam

Three years of field trial along with DSSAT v4.6 CERES-Rice model-based simulation experiment was carried out to study the impact of climate change on Sali rice yield under various Representative Concentration Pathways (RCPs) in the agro-climatic conditions of Jorhat, Assam. Field experiments were conducted during kharif, 2017, 2018 and 2019 at the Instructional-Cum-Research (ICR) farm of Assam Agricultural University, Jorhat with three varieties viz., Mahsuri (150 days), Swarna Sub-1 (140-145 days) and TTB-404 (140-145 days); transplanted under three different micro-climatic regimes created by manipulating date of transplanting i.e., 26th June (early), 11th July (mid) and 26th July (late) under split plot experimental design with four replications. The validated model showed a good agreement for estimation of days required to attain different phenological stages with RMSE value 3.5, 2.9 and 2.9 days for Swarna sub-1; 2.4, 3.3 and 4.1 days for Mahsuri and 3.7, 2.6 and 2.4 days for TTB-404, respectively for panicle initiation, anthesis and physiological maturity. The overall d-stat value varied within 0.53 to 0.85 for phenology and 0.68 to 0.79 for grain yield. The ensemble weather data under four RCPs revealed an increase in mean maximum (0.3 to 3.0°C) and minimum (0.8 to 3.5°C) temperatures along with rainfall (11.8 to 43.4%) during the crop growing period compared to experimentation period (i.e. 2017-19) in three projected years. The grain yield of Sali rice showed positive deviation in all four RCPs and projected years under successive transplanting dates. The overall results reveal an increase in mean temperature up to 3°C during the crop growing period has no substantial adverse impact on grain yield of Sali rice under the agro-climatic condition of Jorhat, Assam

NIASM Annual Report 2011-12

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Temperature-dependent reproduction of <i>S</i>. <i>litura</i>.

<p>Total egg production curve, fitted function: exponential polynomial model (a); and Age-related oviposition rate, fitted curve: Gamma distribution function (b). The upper and lower 95% confidence intervals of the model are indicated. The dots are observed data points.</p

Life table parameters of <i>S</i>. <i>litura</i> estimated at six constant temperatures.

<p>Intrinsic rate of natural increase (a), Net reproduction rate (b), Gross reproductive rate (c), Mean generation time (d), Finite rate of increase (e), and Doubling time (f).</p

Temperature-dependent senescence rates (1/ day) for adults of <i>S</i>. <i>litura</i>.

<p>Female(a) and Male (b). Fitted curves: Modified Sharpe and DeMichele model for both sexes. The upper and lower 95% confidence intervals of the model are indicated. Bars represent standard deviation of the mean.</p

Temperature-dependent mortality rates of immature life stages S. litura.

<p>Egg (a), Larva (b) and Pupa (c). Fitted curves: Wang model for all immature stages. The upper and lower 95% confidence intervals of the model are indicated. Markers are observed means, bars represent standard deviation.</p

Change in number of generations per year of <i>S</i>. <i>litura</i> in soybean growing areas of India based on generation index (GI).

<p>Current climatic conditions (a), Future climatic conditions (b), and Absolute change in GI (c). Economic damage is most likely to occur in the regions with generation index values > 7.0.</p

Scheme of model implementation for estimating temperature-dependent <i>S</i>. <i>litura</i> population growth.

<p>Scheme of model implementation for estimating temperature-dependent <i>S</i>. <i>litura</i> population growth.</p

Comparisons between the developmental effects of diurnal temperature fluctuations predicted from models based on thermal reaction norms designed for constant temperatures with those observed in fluctuating temperatures.

<p>Comparisons between the developmental effects of diurnal temperature fluctuations predicted from models based on thermal reaction norms designed for constant temperatures with those observed in fluctuating temperatures.</p