Interaction of Abiotic Factors on Population of Insect Pests and its Natural Enemies in Bt and Non Bt Cotton G. R. BHANDERI, R. D. PATEL, H. R. DESAI, PRASHANT SANDIPAN AND B. G. SOLANKI Department of Entomology, Main Cotton Research Station, Navsari Agricultural University, Surat-395007 Advances in Life Sciences 5(12), Print : ISSN 2278-3849, 5327-5336, 2016 ABSTRACT Field trial was conducted to determine the effect of ecological factors on the incidence of insect pests on two hybrids of Bt and one non Bt cotton. Sucking insect pest viz. leafhopper, whitefly, thrips, aphid and mealybug remained active throughout the crop season with little differences among them and between Bt & non Bt version. Sucking pests was active from 31 st to 52 nd SMW (SMW i.e. July to December). The peak population of aphid was observed in 48 th SMW while leafhopper population reached to peak in 36 th SMW. The higher population of thrips was observed in 32 nd SMW while, whitefly incidence started from 33 rd SMW and remained below ETL during the season. Mealybug was found from 42 nd to 52 nd SMW. Predators of pests, lady bird beetle and Chrysoperla observed from 33 rd to 52 nd whereas spiders population started from the 31 st to 52 nd SMW. The correlation between predators (LBB and Chrysoperla) and aphid was found highly significant and positive. Aphid, whitefly and mealybug population were highly significant and negatively associated with minimum temperature and morning RH. Leafhopper showed significant positive correlation with minimum temperature and morning RH. Thrips population was highly significant and negatively correlated with maximum temperature and sunshine hours while it was positive correlated with minimum temperature, morning RH and evening RH. The bollworms were active 38 th to 48 th SMW but population of H. armigera; E. vittella and S. litura were peak in 43 th , 45th and 41 th SMW, respectively on non Bt version (DCH 32). The incidence of S. litura was almost nil throughout the season on RCH 2 BG I. Negligible population of H. armigera and E. vittella was observed on RCH 2 BG I but peak population was recorded in 43 rd and 46 th SMW, respectively. Incidence of Spodoptera was almost nil throughout the crop period in RCH 2 BG I. On RCH 2 BG II, the incidence of H. armigera; E. vittella and S. litura was almost nil throughout the season. Pink bollworm larvae and damage were observed early in 38 th SMW and continued till crop end on both Bt and non Bt version. E. vittella larval population showed negative and highly significant correlation with sunshine hours. The pink bollworm larval population showed positive correlation with maximum temperature. Moth catches of H. armigera and P. gossypiella showed highly significant and negative correlation with minimum temperature and morning relative humidity whereas; E. vittella showed significant negative correlation with maximum temperature. S. litura moth catches showed highly significant and positive association with maximum temperature Key words Abiotic factors, Bt Cotton, Non Bt Cotton, Insect pests, Population dynamics, LBB, Chrysoperla, Spider, SMW Cotton is an important natural fibre crop cultivated in varying climatic condition of tropics as well sub- tropic regions of more than 83 countries all over the world. Cotton plays a key role in the national economy in terms of generation of direct and indirect employment in the Agricultural and Industrial sectors. Among the several constraints for low yields, pest menace under the influence of climatic factors, at diverse stages of crop growth is one of the factors limiting its agricultural productivity (Oerke et al., 1994). In case of cotton, pest damage varies significantly in different agro-climatic regions across the country mainly due to differential impacts of several abiotic factors such as humidity, temperature and rainfall (Reed and Pawar, 1982 and Sharma, 2005). This has major inference for the intensification of yield losses due to potential changes in crop diversity and increased incidence of insect-pests in the perspective of imminent climate change. Among the insect pests, a complex of sucking pests viz ., whitefly, Bemisia tabaci (Gennadius), aphid, Aphis gossypii (Glover), green leafhopper, Amrasca biguttula biguttula (Ishida) and thrips, Thrips tabaci (Lindeman), mealybug, Phenacoccus solenopsis Tinsley and bollworm complex viz., Helicoverpa armigera (Hubner), Earias vittella (Fab.) , Spodoptera litura (Fabricius) and Pectinophora gossypiella (Saund) occupy major pest status and cause considerable damage in cotton. The sucking insect pests are reported to cause gradual retardation in plant vigor and deterioration of cotton lint quality as well as quantity (Amin et al., 2008; Shah, 2014). This insect pest not only desaps the host plant but also facilitates transmission of cotton leaf curl