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In the recent years, incidence of the leafhopper, Amrasca devastans (Distant) in cotton has been prevalent from vegetative to reproductive phase of crop growth. The loss in seed cotton yield due to leaf hopper is accounted to 390 kg ha-1 and 330 kg ha-1. In India 45 per cent of the pesticides are applied to cotton. Hence, development of a resistant / tolerant cultivar is the need of the hour to to reduce three ‘ R ’ viz., Resistance, Resurgence and Residues in biota. Screening of twenty six cotton accessions against the leafhopper, A. devastans (Distant) was carried out by following ICCC grades. The susceptiblity of cotton entries varied significantly. Based on the resistance index the entries were grouped under five categories as, Highly resistant- KC 2, SVPR 2; Resistant-TKH 1128: Intermediate- MCU 5, MCU 10, NISD 2, TKH 1143,TKH 1175: Susceptible- TKH 1789, TKH 1173, TKH 1174, TKH 1178, TKH 1179, TKH 1185, TKH 1186, TKH 1209, TKH 1225, TKH 1233 and Highly susceptible- ICMF 20, LRA 5166, TKH 1133, TKH 1172, TKH 1176, TKH 1182, TKH 1197, TKH 1198. Studies on the mechanism of resistance revealed that leafhoppers discriminated cotton entries for orientation and settling and feeding. Highly susceptible entiries were preferred for settling and feeding. Varieties less preferred for settling were less preferred for oviposition too. Since antixenosis and antibiosis were considered for mechanism of resistance various plant parameters viz., Plant height, internodal length, petiole length, leaf area, thickness of leaf, trichome density on the ventral surface of the leaves, hair length, hair density on mid-vein, distance between bases of hairs in mid vein, chlorophyll content, moisture content and protein content were estimated and correlated with leafhopper ovipostion and damage caused. Plant height, internodal length, trichome density on the ventral surface of the leaves, hair length, hair density on mid-vein had negative association with leafhopper damage and oviposition by leafhopper; leaf area, leaf thickness and protein content had no significant association. Susceptible entries had less chlorophyll and more moisture.
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