INTRODUCTION Cotton (Gossypium spp) is commonly known as “White gold” of India. In India Cotton is cultivated on a 12.2 million ha area with a production of 347.05 lakh bales (170kg) and a productivity of 484 kg lint/ha-1 (Sarma et al., 2021). In India, Telangana has the largest acreage of 20.51 lakh ha with production and productivity of 65.87 lakh bales and 545.97 kg ha-1, respectively (Agriculture Statistics at Glance, 2021-2022). Bt-Cotton is more susceptible to attack by sucking insect pest complex viz., Leafhoppers, Amrasca biguttula biguttula (Ishida); Aphids, Aphis gossypii (Glover); Thrips, Thrips tabaci (Lindeman) and Whiteflies, Bemisia tabaci (Gennadius) compared to Desi Cotton. Cotton has been attacked by around 162 species of insects and mites in India, Pest control is necessary for a higher cotton output since pests damage the crop and diminish yield. Due to the Leafhopper, Amrasca biguttula biguttula damage estimated yield loss was reported at about 18.78 percent, whereas due to the sucking pests damage estimated yield loss decreased by about 8.45 q/ha (Sarma et al., 2021). Among all other sucking pests, the cotton leafhopper is an alarming pest throughout the season both the nymphs and adult stages harm the plants by sucking the sap from leaves and transmitting various viruses and causing phytotoxic symptoms known as hopper burn which results in complete desiccation and has become one of the limiting factors in economic productivity of the crop, reducing the growth and yield. Leafhoppers are undoubtedly more severe among the many destructive sucking pests of cotton. Hence, suitable techniques to manage the sucking pest population on transgenic cotton are needed (Bheemanna et al., 2015). Due to the continuous and indiscriminate use of synthetic insecticides, there is resistance and hence the efficacy has become less reliable. To overcome this problem discovery of novel substances with different biochemical targets are needed. Novel molecules are effective at lower doses and have less exposure to the environment (Udikeri et al., 2010). Increasing plant density in cotton could be a viable alternative for increasing production and net profits (Naik et al., 2017). Plant spacing has a key role in managing optimum plant density according to the requirement of variety under consideration to boost cotton productivity, especially under irrigated conditions (Nadeem et al., 2010). High-Density Planting System (HDPS) is popularly known as Ultra Narrow Row (UNR) Cotton, which has row spacings less than 20 cm resulting in 2 to 2.5 lakh plants ha-1, while conventional cotton is generally planted in rows at 90 to 100 cm apart it has a plant population of about 1 lakh plants ha-1. The main advantage of UNR spacing is earliness as it needs fewer bolls per plant to achieve the same yield as that of conventional cotton and the crop need not be maintained for the late-formed bolls to mature. Compared to conventionally planted cotton, UNR Cotton plants produce fewer bolls but a higher percentage of total bolls are retained in the first sympodial position than in the second position (Vories and Glover 2006). Adoption of narrow plant spacing with increased plant density may create the congenial condition for sucking pest population build-up in cotton (Singh et al., 2015). In this connection, the present study was carried out to evaluate the per cent reduction of leafhopper population Bt-Cotton under the HDPS and normal with different new molecule insecticides. MATERIALS AND METHODS The experiment was carried out during Kharif, 2021 at Regional Agricultural Research Station (RARS), Palem, PJTSAU, Telangana. The field experiment was laid out in Split Plot Design (SPD) with a plot size of 500 m2with eight treatments, each replicated thrice, the size of each treatment plot was 6.0 m × 5.0 m (30m2). The spacing between row to row and plant to plant was kept 75 cm × 10 cm (HDPS) and 90 cm × 60 cm (Normal) respectively. Cotton hybrid NCS-2778 is the test hybrid chosen for the present investigation. To determine the efficacy of insecticides, two sprays on Bt-cotton were applied. The first spray was carried out based on the Economic Threshold Level (ETL) of leafhoppers and the second spray was followed by subsequently after 10 days interval. The pre-count (1 day before spray) and post-count (3rd and 7th days after spray) of the leafhopper population was recorded by counting the top 3 open leaves of five randomly selected plants of each plot and per cent population reduction over control was calculated. All the molecules under study were applied as a foliar spray using a knapsack sprayer. All recommended package of practices were applied to maintain the good plant stand throughout the crop growth period. Treatments details are given in the table below (Table. 1). Statistical analysis: The percentage reduction of the pest population in each observation was calculated by using Abbott’s formula as given by Flemming and Ratnakaran (1985). Population reduction in percentage (PRP)= 1-(Post-TPT)/(Pre-TPT)* (Pre-TPC)/(Post-TPC)*100 Post treatment population in the treatment = Post-TPT; Pre-treatment population in the treatment = Pre-TPT; Pre-treatment population in control = Pre-TPC; Post-treatment population in control = Post-TPC. PRP values were transformed into corresponding angular values and subjected to ANOVA using MS-Excel and R studio, respectively. RESULTS AND DISCUSSION The results of the study on the efficacy of new molecule insecticides against cotton leafhoppers are presented in the given tables (Table 2). In pre count the average leafhopper population count per five random plants was recorded in the range of 5.956 to 10.563 and 7.06 to 10.10 per 3 leaves in HDPS and Normal planting, respectively. In insecticidal treatments against the leafhopper population varied significantly at all the post-treatment counts of HDPS and Normal planting. HDPS and Normal planting at 3 DAS (days after spraying) the maximum reduction of the pest over control was recorded with 97.265 and 96.995 per cent in Flonicamid 50 WG, respectively and it has shown supremacy over other treatments, these findings are agreement with Kumari et al. (2021) who reported that flonicamid 50 WG has showed the reduction of leafhoppers populations effectively than other treatments which was followed by Afidopyropen 50 OD with 96.350 and 92.975 per cent, respectively. Acetamiprid 20 SP with 86.140 and 85.605 per cent, respectively and Clothianidin 50 WDG with 73.215 and 75.145 per cent followed by Imidacloprid 17.8 SL with 68.285 and 64.630 per cent respectively and statistically varied with all other treatments. The minimum reduction of leaf hopper population was observed in Diafenthiuron 50 WP with 58.450 and 57.080 per cent, respectively which was followed by Cyantraniliprole 10.26 OD with 56.475 and 53.480 per cent, respectively. In both HDPS and Normal planting 7 DAS (days after spraying), Flonicamid 50 WG was shown supremacy in reducing leafhopper population over control with 97.070 and 89.620 per cent, respectively which was followed by Afidopyropen 50 OD with 93.195 and 90.295 per cent, respectively which was followed by Acetamiprid 20 SP with the 81.025 and 81.810 per cent, respectively and Clothianidin 50 WDG with reduction of 71.120 and 70.005 per cent, respectively. The minimum reduction of leafhopper population was observed in Imidacloprid 17.8 SL with the reduction of 61.765 and 65.310 per cent, respectively which is followed by Diafenthiuron 50 WP with 51.635 and 54.300 per cent and Cyantraniliprole 10.26 OD with the reduction of 54.975 and 49.595 per cent, respectively these are found to be least effective but significantly and statistically superior over the control. The present study results are comparable with the findings of Meghana et al. (2018) who reported that maximum mortality of jassids was found in Flonicamid treated plots. Baraskar and Paradkar (2020) reported that Flonicamid 50WG was effective in controlling the cotton leafhopper population. Similar results are also reported by Bharpoda et al. (2014) and the results derive support from the findings of Nemade et al. (2017) reported that Flonicamid gives the best results by lowering the leafhoppers population. Kadam et al. (2014) reported that Clothianidin and Imidacloprid were affecting reducing the populations of leafhoppers and the present findings are in line with the findings of Suman et al. (2021) reported that the Afidopyropen was found to be effective against leafhopper population. Yield. The data on (Table 4) Cotton yield in HDPS and Normal spacing revealed that all the insecticidal treatments registered significantly higher cotton yield over untreated control. Among the all treatments, Flonicamid 50 WG @ 150gha-1 recorded higher cotton yield (33.18 q ha-1)and (22.76 q ha-1) respectively, followed by Afidopyropen 50OD @ 1000 mlha-1 (29.88 q ha-1) and (22.43 q ha-1), respectively and were on par with each other. The leastcotton yield was obtained in Cyantraniliprole 10.26 OD @ 500 ml ha-1 (20.68 q ha-1) and (17.44 q ha-1), respectively. The highest Cost-Benefit Ratio was achieved with Acetamiprid (Rs. 1:93.81) and which was followed by Imidacloprid (Rs. 1:76.01) which is followed by Flonicamid (Rs.1:40.92), respectively.