Genetic diversity in chestnuts of Kashmir valley A study was carried out in the experimental area of Ayub Agricultural Research Institute Faisalabad during (2012) to determine the role of morphological and biochemical parameters of Bt cotton genotypes influencing resistance against thrips Thrips tabaci (Lind). Six advance lines and one Bt cotton approved variety IR-NIBGE-5, SITARA 10-M, SITARA 11-M, PB-38, SITARA-009, IR-NIBGE-4 and BT-121 respectively were planted in Randomized Complete Block Design with 3 replications. Varieties differ significantly in response to thrips population on per leaf basis. SITARA 10-M showed maximum population of thrips (5.01/leaf) and did show significant difference with all other genotypes. Various morphological and biochemical traits also differ significantly among seven genotypes of cotton. Gossypol glands on Leaf lamina and phosphorus contents of leaves showed negative and highly significant correlation -0.447 and -0.490 respectively with the thrips population while hair density on veins and lamina and hair length on lamina showed positive and significant correlation 0.806, 0.574 and 0.45 respectively with the thrips population. All others parameters showed non-significant correlation with the thrips population. The R 2 values, computed together for multiple regression analysis for thrips population indicated that hair density on vein was the most important factor which contributed maximum i.e. 58.2% in pest population fluctuation of the pest. Gossypol gland on lamina was the second important factor showing impact of 20%, Hair density on lamina and hair length on lamina showed 6.90% and 0.30 % impact in per unit change in pest population. Phosphorus contents showed 24% impact in per unit change in the pest density. Principle component analysis of morphological and chemical factors revealed that gossypol gland on lamina showed contrasting behavior having maximum variance value 95.159%. Hair density on vein also showed contrasting behavior with variance values of 3.741%. Hair density on lamina, hair length of lamina and Phosphorus content was not an important factor due to minimum variance value of 0.804%, 0.234% and 0.064%. Morphological and biochemical take part in resistance against pest which can be used as important tool in integrated pest management model. Keywords: Cotton, morphology, resistance, thrips, insecticide INTRODUCTION Thrips infestation has repeatedly caused severe damage to young cotton plants (Arif et al., 2005). A study in Pakistan revealed 37.6% loss in yield of seed cotton by combined attack of Thrips 14.6 per leaf (Saleem et al., 2013) It has been observed that Thrips tabaci (Lind.) is the specie which caused serious destruction to cotton crop in Pakistan (Baloch and Soomro, 1980). According to Williams (2006) during 2005 the greatest losses from thrips occurred in Virginia and Oklahoma with 3.66 and 3%, respectively. Ottens et al. (2004) reported that in Georgia severe infestations can cause yield reduction as high as 50-60% if not controlled. Transgenic Bt cotton genotypes can effectively control specific lepidopteran species (Cotton bollworm Helicoverpa armigera and pink bollworm Pectinophora gossypiella (Arshad and Suhail, 2010) but they are not effective in controlling sucking insect pests (Hofs et al., 2004). Hence Bt genotypes demands regular use of pesticides for effective management of thrips (Hilder and Boulter, 1999). The reduced use of pesticides in Bt cotton increases the population sucking insect pests (Men et al., 2005) so sucking insect pests majorly thrips, jassid and white fly have become a major significant part of Bt cotton insect pest community (Wu et al., 2002). As another aim of Bt cotton is to reduce pesticide usage for environmental safety, there is a need for the establishment of environmental friendly, safer, long lasting and more reliable control measures for the control of sucking insect pests particularly thrips (Ashfaq et al., 2010). Plant resistance is an important factor of controlling agricultural pests. The resistance may be due to physico- morphic and biochemical characters of plant (Raza et al., Pak. J. Agri. Sci., Vol. 51(3), 725-731; 2014 ISSN (Print) 0552-9034, ISSN (Online) 2076-0906 http://www.pakjas.com.pk THE ROLE OF MORPHOLOGICAL AND CHEMICAL PLANT TRAITS IMPARTING RESISTANCE IN BT COTTON GENOTYPES AGAINST THRIPS, Thrips tabaci (Lind.) Muhammad Ahsan Khan 1,* , Amjad Ali 2 , Muhammad Aslam 2 , Zain Tahir 1 , Muhammad Musa Khan 1 and Imran Nadeem 3 1 Department of Entomology, University of Agriculture, Faisalabad, Pakistan; 2 Pest Warning & Quality Control of Pesticide, Dept. of Agriculture, Lahore, Punjab, Pakistan; 3 Institute of Entomology, Ayub Agricultural Research Institute, Faisalabad, Pakistan * Corresponding author’s e-mail: drmakhanz@yahoo.com