SEASONAL INCIDENCE, FIELD SCREENING OF LOCAL LANDRACES, AND BIOCHEMICAL BASIS OF RESISTANCE IN RICE AGAINST PADDY EARHEAD BUG, LEPTOCORISA ORATORIUS (FABRICIUS) (HEMIPTERA: ALYDIDAE)
Abstract
The paddy earhead bug, Leptocorisa oratorius (Fabricius) (Hemiptera: Alydidae), is a chronically destructive pest of rice (Oryza sativa L.) in India, with documented yield losses of 15–30% under moderate infestation and up to 80% under severe epidemics. A comprehensive investigation integrating seasonal population dynamics, large-scale varietal screening, and biochemical resistance characterisation was conducted at the College of Agriculture, V.C. Farm, Mandya, Karnataka, during Kharif 2021. Seasonal incidence studies recorded a peak population of 7.63 bugs/10 hills on the susceptible check Jaya during the last week of November, coinciding with the milky grain stage, and a substantially lower peak of 1.53 bugs/10 hills on IR 64. Pearson's correlation analysis identified maximum temperature as exerting a significant negative influence on bug density (r = −0.78** on Jaya; r = −0.67** on IR 64), while afternoon relative humidity (r = +0.72**; +0.68**) and sunshine hours (r = +0.69**; +0.72**) were significantly positive predictors, providing a meteorological basis for pest forewarning. Field screening of 50 local landraces categorised 15 as Resistant (R), 10 as Moderately Resistant (MR), 20 as Moderately Susceptible (MS), 3 as Susceptible (S), and 2 as Highly Susceptible (HS). Screening of 37 Advanced Varietal Trial (AVT) genotypes yielded 4 R, 11 MR, 14 MS, 5 S, and 3 HS entries. Biochemical analysis of 18 representative genotypes at the milky grain stage revealed that resistant accessions were characterized by elevated levels of total phenols (up to 1.49 mg g⁻¹), tannins (up to 4.85 mg g⁻¹), total free amino acids (TFA; up to 10.78 mg g⁻¹), and potassium (K; up to 3.54%) — all significantly and negatively correlated with grain damage (r = −0.86**, −0.94**, −0.95**, −0.93**, respectively). Susceptible genotypes accumulated higher total soluble sugars (TSS), total reducing sugars (TRS), crude proteins, nitrogen (N), and phosphorus (P), all of which showed highly significant positive correlations with grain damage (r = +0.95**, +0.97**, +0.98**, +0.95**, +0.87**, respectively). The resistant landraces Kave kantak, Nagland paddy, and Narali, alongside their distinctive biochemical profiles, provide a robust scientific foundation for developing durable pest-resistant rice cultivars and implementing ecologically rational integrated pest management programmes.