Impact of Weather Variability on Insect Pests and Natural Enemies in Linum usitatissimum L.

Experiments were conducted at the Research Farm of Bihar Agricultural University, Sabour, Bhagalpur, Bihar, India, to study the population dynamics of insect pests in linseed varieties Neelum and Sabour Tisi-1 during the Rabi seasons of 2020-21, 2021-22, 2022-23, and 2023-24, using a plot size of 1000 m². Six insect pests belonging to six families and genera were recorded: linseed bud fly (Dasyneura lini Barnes), capsule borer (Helicoverpa armigera Hubner), cutworm (Agrotis ipsilon Hufnagel), melon thrips (Thrips palmi Karny), blossom thrips (Frankliniella schultzei Trybom), and green peach aphid (Myzus persicae Sulzer). Additionally, two natural enemies were observed: the ladybird beetles (Coccinella septempunctata L. and Menochilus sexmaculatus F.) and lynx spider (Oxyopes spp.), all associated with the linseed varieties Neelum and Sabour Tisi-1. Among the insect pests, the linseed bud fly (Dasyneura lini Barnes) was identified as the most dominant pest, followed by thrips and the capsule borer. The highest bud fly infestation (26.84%) was observed in the Neelum variety at the dough stage, which was 2.83 times higher than in the Sabour Tisi-1 variety. The maximum number of nymphs and adult thrips (15.68 per plant) was recorded in the Neelum variety, which was 2.40 times higher than in Sabour Tisi-1. The highest number of grubs and adult ladybird beetles was observed at 1.08 per plant and 1.42 per plant in the Neelum and Sabour Tisi-1 varieties, respectively. Bud fly infestation was highly significantly and positively correlated with both maximum and minimum temperatures (r = 0.90 and r = 0.93 in Neelum; r = 0.92 and r = 0.92 in Sabour Tisi-1). Conversely, it was highly significantly and negatively correlated with maximum and minimum relative humidity (r = -0.78 and r = -0.76 in Neelum; r = -0.82 and r = -0.76 in Sabour Tisi-1). In conclusion, the Neelum variety was found to be more susceptible to insect pest attacks, followed by the Sabour Tisi-1 variety.