Vol. 12, Special Issue 10 (2023)

Author(s):
Koushik Garai

Abstract:
Seasonal incidence and distribution pattern of insect pest of onion ecosystem was studied at Horticulture Research farm, Palli Siksha Bhavana (Institute of Agriculture), Visva-Bharati, Sriniketan, West Bengal during rabi season of 2021-22. The result of field experiment revealed that the highest population of thrips was 18.86 thrips per plant on fourth week of December (52^nd SMW). Thereafter the nymph and adult population gradually declined and no population found since 3^rd week of February (7^th SMW) till harvesting. The population of flea beetle was highest (1.71 adult /plant) on second week of January (2^nd SMW) and the maximum population of flea beetle (2.14/ plant) was observed in the second week of January (2^nd SMW). Different indices of dispersion i.e mean, variance, variance-mean radio, dispersion parameter ‘K’, David and Moore’s index, Lexis Index, Charlier coefficient, Index of dispersion, Lloyd mean crowding index showed aggregative, clumped and contagious nature of distribution of thrips, flea beetle and grasshopper in crop growing season. But it was found that majority of the calculated "K" values for standard weeks slightly different from the negative binomial aggregative kind of dispersion.