Seasonal incidence and distribution pattern of insect pest infesting onion ecosystem in the red lateritic zone of West Bengal

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 (52nd SMW). Thereafter the nymph and adult population gradually declined and no population found since 3rd week of February (7th SMW) till harvesting. The population of flea beetle was highest (1.71 adult /plant) on second week of January (2nd SMW) and the maximum population of flea beetle (2.14/ plant) was observed in the second week of January (2nd 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