Spatio-Temporal Dynamics of Spider Populations in Bt and Non-Bt Cotton Agroecosystems of South Gujarat, India: Influence of Biotic and Abiotic Factors

A field investigation studied the seasonal abundance and activity of spider populations in cotton fields across treatment plots in Surat and Bharuch, Gujarat. In Surat, spider activity in unprotected plots of the Bt cotton hybrid RCH 2 BG II was noted from the 29th to the 1st Standard Meteorological Week (SMW), peaking (>0.80 spiders/plant) between the 46th (second week of November) and 51st SMW (third week of December). In protected plots of the same hybrid, spiders were active from the 31st to the 1st SMW, with peak densities observed from the 46th to 1st SMW (first week of January). Similarly, in non-transgenic Suraj variety, unprotected plots showed spider activity from the 29th to the 1st SMW, peaking from the 41st to 51st SMW. In Bharuch, spider activity spanned from the 32nd to the 52nd SMW in all plots. In unprotected plots of RCH 2 BG II, peak spider activity (>0.80 spiders/plant) occurred from the 44th (fourth week of October) to the 52nd SMW. Protected plots of the same hybrid peaked from the 47th to the 52nd SMW. In Suraj, unprotected plots peaked from the 44th (fifth week of October) to the 52nd SMW, while protected plots peaked from the 46th to the 52nd SMW. Positive correlations were found between spider populations and pest species like aphids, jassids, whiteflies, and mealybugs, as well as abiotic factors such as maximum temperature and sunshine hours in Surat. In contrast, significant negative correlations were noted with morning and evening relative humidity, rainfall, and rainy days. At Bharuch, spider populations positively correlated with aphids, whiteflies, mealybugs, and sunshine hours, while negatively correlating with minimum temperature, relative humidity, and rainy days.