Spatial distribution of Thrips tabaci Lindeman on rabi onion in north western Indian Himalayan regions

Abstract

Abstract Spatial distribution of Thrips tabaci Lindeman on rabi onion was assessed in mid-hill regions of Himachal Pradesh, representing north-western Indian Himalayas. Thrips followed negative binomial distribution in onion. Based on the Lewis index, Index of dispersion, Morisita coefficient of dispersion, Lloyd’s mean crowding and Index of patchiness it was observed that in early stages of crop growth stages of rabi onion, thrips were distributed randomly whereas in later crop stages, thrips distribution was aggregated/ overdispersed/ clumped. Aggregated distribution of thrips was also confirmed by Taylor’s power law and Iwao’s patchiness regression index with the corresponding values of 1.29 and 2.65. For estimation of thrips population in vegetative, bulb initiation and bulb development stage, the mean number of samples needed were 15476, 760 and 270, respectively at P = 0.1 (precision level of 90%). Whereas at 80% (P = 0.2), relatively small number of samples were needed (869, 190 and 68) for corresponding crop stages.