Abstract

                                Field monitoring of cotton whitefly, Bemisia tabaci with yellow cylindrical sticky traps at TamilNadu Agricultural University, Coimbatore in a cotton based gardenland cropping system revealed that the population of whitefly showed the same level of dispersal behaviour for the entire period of observation between 1991-1994 with differences in the numerical population level. Residual population was observed on weed hosts viz. Parthenium hysterophorus, Sanchus oleraceus, Boerhaavia diffusa and Trianthema portulacastrum in non-crop periods. The population of whitefly reached the outbreak condition on cotton and soyabean crops during November-February months. Crops raised before, after and or along with cotton such as sunflower and groundnut asssisted the whitefly to sustain; pulses and sesame helped to establish its population during different months. Rabi and winter season sown" crops recorded heavy population build ups owing to the favourable weather factors prevailed during these crop stand periods. Low rainfall, high temperature, moderate relative humidity and high sunshine levels noticed during September to March boosted the quick growth and development of B.tabaci. From the middle of May the population started declining with the onset of South-West monsoon.

Key words : Cotton, Whitefly, Population, Host crops. Dispersal, Establishment, Migration