POPULATION DYNAMICS, INSECTICIDE RESISTANCE/SUSCEPTIBILITY AND CHEMICAL CONTROL OF THRIPS, SCIRTOTHRIPS DORSALIS HOOD (THYSANOPTERA: THRIPIDAE) INFESTING CHILLI
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Date
2018-11-14
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UNIVERSITY OF AGRICULTURAL SCIENCES GKVK, BENGALURU
Abstract
Investigations were carried out on population dynamics, insecticide
resistance/susceptibility and chemical control of chilli thrips, Scirtothrips dorsalis at
three locations, Kotagal (Chintamani), IIHR & GKVK in Bengaluru during 2015-17. The
peak activity of thrips on kharif crops across three locations was more apparent during
October-November period when crop age was 90-120/150 days and on rabi-summer
crops during February-March on 100-120 days old crop. Influence of abiotic (maximum
temperature, bright sunshine hours, evaporation) and biotic (natural enemies) factors
significantly influenced the buildup of thrips, while minimum temperature, RH, rainfall
and wind speed adversely affected thrips activity. Step-wise regression analysis revealed
more significant positive influence of maximum temperature, minimum temperature,
natural enemies, evaporation and afternoon relative humidity, while rainfall influenced
thrips activity negatively. At Kotagal, application of spinosad resulted in maximum
reduction of thrips (91%) after 7 days followed by acephate (72%), dimethoate (69%),
imidacloprid (61%), fipronil (61%), diafenthiuron (60%), clothianidin (55%) and
thiamethoxam (55%). Spinosad application continued to record significant decline in
thrips population up to 10 days, which resulted in higher green fruit yield of 9.02
tonnes/acre. At IIHR also, within one week after application, spinosad caused >87%
reduction in thrips population and fruit yield obtained was also highest (13 tonnes/acre).
Among the insecticides assayed in laboratory, spinosad was found more toxic to thrips
with the lower LC50 values ranging from 44.28 to 46.40 ppm. Acephate was least toxic
with higher LC50 values between 572.80 and 602.80 ppm. Order of toxicity of other
insecticides was; imidacloprid (47.66-53.94ppm), fipronil (51.97-62.40ppm), clothianidin
(95.72-101.90ppm) and diafenthiuron (230.56- 325.65ppm). Based on LC50 and LC90
values, the toxicity of these insecticides to populations of thrips across the three study
locations was observed to be similar (1.02-1.41 and 1.03-1.37, respectively)