PREVALENCE OF PESTICIDE TOLERANCE IN SOIL BACTERIA FROM DARJEELING HIMALAYAS: A GROWING CONCERN OF GRASSHOPPER EFFECT

Abstract

Agricultural development involves the use of pesticides that have ended up in the soil or water bodies. These chemicals can accumulate and control microbial population by imposing tolerance to them. Pesticides can accumulate in soil or water by a multi-hopping phenomenon, termed the ‘Grasshopper effect’ that requires one or more volatilization-migration-deposition cycles. This study is an attempt at assessing the possible occurrence of this phenomenon in the Darjeeling Himalayas. A total of 39 sites of varied biotopes were sampled and their soil bacterial populations assessed based on the acquired degree of tolerance against pesticides. Soil microbial consortia isolated from all the regions showed total tolerance against the volatile pesticides emamectin benzoate, thiamethoxam, quinalphos, deltamethrin, spiromesifen and flubendiamide. Out of 47 isolates obtained, 29 exhibited full tolerance against them. Based on altitudinal zones, all the isolates from below <2000 ft depicted no inhibition zones against the tested pesticides while some inhibition was observed for the isolates from 2000-4000 ft (57.14%), 4000-6000 ft (28.57%), 8000-10000 ft (14.29%) and >10000 ft (75%). This work provides evidence for the occurrence of the ‘Grasshopper effect’ in the Darjeeling Himalayas facilitating the long-range transport, deposition and accumulation of harmful volatile pesticides in the region.