author(s)
E Akhila, S Upendhar, K Vani Sree and B Vidhya Sagar

abstract
The present study aimed at the screening of popular Bt cotton hybrids against leafhoppers, Amrasca biguttula biguttula (Ishida) incidence at College farm, College of Agriculture, Rajendranagar, Hyderabad during kharif 2019-20. Eight transgenic cotton hybrids (Bioseed-7215-2, MH-5343, RCH-668, MRC-7347, PRCH-331, RCH-386, ROHINI-456, RCH-659) were sown and maintained without application of any insecticide till the maturity of the crop. Field data of leafhopper was collected from the occurrence of the pests after seedling emergence to till harvest at weekly intervals. The peak activity of leafhoppers was recorded during the 37^th standard week to 44^th standard week with a peak population of 10.13/3 leaves/plant in Bioseed-7215-2 and MRC-7347 during the 37^th standard week among all the hybrids. While RCH-668 (6.93/3 leaves) showed a minimum leafhopper population build-up. Further, the leafhopper population was correlated with abiotic factors. The maximum temperature had a significant positive response on the leafhopper population. Whereas, minimum temperature, morning relative humidity, evening relative humidity and rainfall also showed positive correlation but non significantly. The regression studies revealed that all the weather parameters together contribute 75 percent (R² = 0.75) of the total variation in the leafhopper population.