Visva-Bharati University

Rice yellow stem borer (YSB), Scirpophaga incertulas (Walker), is one of the most destructive insect pests of rice across diverse rice ecosystems. The pest damages the rice crop at both the seedling and maturity stages, resulting in severe yield losses. Host Plant Resistance (HPR) is the economical, sustainable, and eco-friendly component of integrated pest management (IPM). A comprehensive understanding of population genetics and the genetic diversity of YSB is essential for identifying tolerant donors and strengthening the resistance breeding programmes. In the present study, the genetic diversity of YSB populations collected from different locations of India was analysed using the mitochondrial Cytochrome c oxidase subunit I (COX1) gene, and compared with global YSB populations. Phylogenetic analysis revealed the presence of two major clades among the global YSB populations. Nucleotide sequence analysis detected 60 mutations and 56 variable sites (polymorphic sites) in the COX1 sequences, with Indian populations exhibiting a comparatively higher number of variable sites. Haplotype analysis identified 38 haplotypes, among which three are major haplotypes (haplotype 24, 32, and 34). The overall haplotype diversity (Hd) and the nucleotide diversity (π) were 0.964 and 0.02182, respectively, while Indian populations exhibited Hd of 0.952 and π of 0.01235, indicating high haplotype diversity with moderate nucleotide divergence. Neutrality tests for Indian populations yielded significantly negative values of Tajima’s D (-2.21303), Fu and Li’s D (-4.40753), and Fu and Li’s F (-4.05701), suggesting an excess of low-frequency polymorphisms and/or localized mutational events. Overall, mitochondrial COX1 gene-based analysis revealed considerable genetic variation among YSB populations in India and across global regions. This study represents one of the first comprehensive reports summarising the genetic variation of YSB populations using the mitochondrial COX1 gene sequences, providing valuable insights for resistance breeding and long-term YSB pest management.

The present work reveals a direct correspondence between modified theories of gravity (cosmology) and entropic cosmology based on the thermodynamics of apparent horizon. It turns out that due to the total differentiable property of entropy, the usual thermodynamic law (used for Einstein gravity) needs to be generalized for modified gravity theories having more than one thermodynamic degree of freedom (d.o.f.). For the modified theories having n number of thermodynamic d.o.f., the corresponding horizon entropy is given by Sh similar to SBH+ terms containing the time derivatives of SBH up to (n-1)-th order, and moreover, the coefficient(s) of the derivative term(s) are proportional to the modification parameter of the gravity theory (compared to the Einstein gravity; SBH is the Bekenstein-Hawking entropy). By identifying the independent thermodynamic variables from the first law of thermodynamics, we show that the equivalent thermodynamic description of modified gravity naturally allows the time derivative of the Bekenstein-Hawking entropy in the horizon entropy.

We investigate the influence of large-scale cosmic web environments on galaxy quenching using a volume-limited, stellar mass-matched galaxy sample from Data Release 18 from the Sloan Digital Sky Survey. Galaxies are classified as residing in sheets, filaments, or clusters based on the eigenvalues of the tidal tensor derived from the smoothed density field. The quenched fraction increases with stellar mass and is highest in clusters, intermediate in filaments, and lowest in sheets, reflecting the increasing efficiency of environmental quenching with density. A flattening of the quenched fraction beyond log10(M star/M circle dot)similar to 10.6 across all environments signals a transition from environment-driven to mass-driven quenching. In contrast, the bulge fraction continues to rise beyond this threshold, indicating a decoupling between the suppression of star formation and morphological transformation. At the high-mass end ( log10(M star/M circle dot)greater than or similar to 11.5 ), both quenched and bulge fractions bifurcate, increasing in clusters but declining in sheets, suggesting a divergent evolutionary pathway where massive galaxies in sheets retain cold gas and disk-like morphologies, potentially sustaining or rejuvenating star formation. The fraction of active galactic nuclei (AGN) also increases with stellar mass and is somewhat higher in sheets than in clusters, indicating enhanced AGN activity in low-density, gas-rich environments. The high-mass trends are independently corroborated by our analysis of specific star formation rate, (u - r) colour, concentration index, and D4000 in the stellar mass-density plane, which show that massive galaxies in sheets remain bluer, younger, more star-forming, and structurally less evolved than their cluster counterparts. Our results highlight the cosmic web as an active driver of galaxy evolution.

We explore the impact of cosmic web environments on galaxy properties such as (u-r)colour, stellar mass, star formation rate, and stellar metallicity, using a stellar mass-matched sample of simulated galaxies from the IllustrisTNG simulation. We use Normalized Mutual Information (NMI) to quantify correlations among galaxy properties and apply Student's t-test to assess the statistical significance of their differences across cosmic web environments. In every case, the null hypothesis is rejected at > 99.99% confidence, providing strong evidence that correlations among galaxy properties are strongly dependent on cosmic web environments.

The cosmological principle, asserting large-scale homogeneity and isotropy, underpins the standard model cosmology. Testing its validity using independent astronomical probes remains crucial for understanding the global structure of the Universe. We investigate the angular distribution of Gamma-Ray Bursts (GRBs) using two of the most comprehensive all-sky datasets available, the BATSE (CGRO) and Fermi GBM catalogs, to test the isotropy of the GRB sky at large angular scales. We perform spherical harmonic decomposition of the GRB sky maps and estimate the dipole and quadrupole amplitudes. Statistical significance is evaluated by comparing the observed multipole amplitudes against distributions derived from 500 Monte Carlo realizations of isotropic skies. Our results show that the observed dipole amplitudes for both BATSE and Fermi GBM datasets lie within the 1 sigma region of their respective null distributions. However, the quadrupole amplitude in the raw, uncorrected BATSE and Fermi GBM skies appears elevated at 3.7 sigma and 3.0 sigma, respectively. After incorporating the BATSE sky exposure function, this apparent quadrupole anisotropy vanishes, indicating that instrumental non-uniformities fully account for the signal in that case. Owing to the absence of a publicly available full-sky exposure model for Fermi GBM, the Fermi analysis is restricted to the raw sky distribution. Our method's reliability is validated through controlled simulations, which show it can detect the injected dipoles in BATSE-sized isotropic skies. These findings reinforce the statistical isotropy of the GRB sky and underscore the importance of accurate exposure corrections in cosmological anisotropy analyses.